Bag with a high vapor barrier effect

Abstract

This utility model relates to a bag consisting of an outer sheet of paper layered over an inner sheet of paper, in which: - each of said outer and inner sheets of paper has a basis weight of 70 to 90 g / m² and is of the semi-stretch type, i.e., it has a tensile strength in the machine direction (MD) of 6.4-7.8 kN / m and a tensile strength in the transverse direction (TD) of 4.7-5.8 kN / m, measured according to ISO 1924-3:2019, - each of said outer and inner sheets of paper is coated on one side with a vapor barrier layer having a basis weight of 10 to 20 g / m², said basis weight being measured according to ISO 536:2019, - said vapor barrier layer comprises a styrene-based polymer dispersion minus a pigment made of clay and calcium carbonate,- said water vapor barrier layer is also coated with at least one water-based hydrophobic wax-type paint layer, such as a polymer wax, which comprises at least one element of the isothiazol-3-one type, for example 1,2-benzisothiazol-3(2H)-one, 5-chloro-2-methyl-2H-isothiazol-3-one (CMIT) and / or 2-methyl-2H-isothiazol-3-one, and mixtures thereof.

Description

Title of the invention: High vapor barrier bag technical field

[0001] The present utility model refers to a bag for transporting materials. In particular, the present utility model relates to a bag for transporting cement or other useful materials in various sectors, whether food, chemical or construction, without plastic elements ("plastic free") and with a high water vapor barrier.

[0002] Prior art.

[0003] Currently, for the transport of cement and other similar materials in the construction sector, as well as for the transport of other goods, for example in the food or chemical sectors, and for the transport of minerals, bags made of paper and plastic are used.

[0004] US 2012 / 251019 describes a recyclable bag for dry-based powders, grains, and particles, having a single minimal layer of high-density porous paper intended to be folded into a sealable bag. At least one layer of high-porosity paper has an adhered layer of a biodegradable hydrophobic material on an outer and / or inner side; furthermore, the adhered layer of biodegradable hydrophobic material includes a series of holes for air passage to ventilate the bag during filling.

[0005] FR 2970952 A1 describes a bag equipped with a valve and comprising a film including a first layer of paper, having an inner and an outer face. A hydrophobic composition is present on a portion of the outer face of the first paper layer such that the coated portion of the outer face has a wetting tension of air less than or equal to the wetting tension of water. The film includes a second layer of paper which is attached to the inner face of the first paper layer by a layer of adhesive dots forming an adhesive layer.

[0006] DE 202014000194U describes a bag comprising at least one layer of paper with A layer that is hermetically sealed towards the inside of the bag; and where the paper layer facing the inside of the bag has an air-permeable zone in the area of ​​the layer that is covered by the paper layer facing the outside of the bag. At least one paper layer, at least in part, has a water-repellent / waterproof coating facing the outside of the bag.

[0007] Generally, bags known in the prior art consist of two superimposed sheets of paper, for example 80 g / m2, between which is inserted a sheet of plastic, generally high-density polyethylene (HDPE), i.e. with a density between 0.945 and 0.965 g / cm3 and a thickness of, for example, between 7 and 12 microns.

[0008] These bags exhibit good resistance to moisture, even when stored for a long time in a humid environment.

[0009] However, the drawback of these bags is that they contain plastic elements; given the very high number of bags of this type used worldwide for the transport of various materials, the fact that they contain plastic elements is a serious environmental problem.

[0010] The Italian patent application published under number IT 102020000013471 in the name of the same applicant as the present application describes a bag without plastic elements, consisting of at least two overlapping sheets of paper, in which the outer sides of said sheets are coated with at least one layer of hydrophobic paint. This gives the bag better protection against moisture.

[0011] Bags made of at least one sheet of semi-stretchable paper on which a protective layer against water vapor is applied are also commercially available; the presence of this protective layer allows the bag to have a significantly improved moisture barrier effect.

[0012] However, the applicant identified the need to produce bags free of plastic elements, which would offer even more effective protection against water vapor than bags known in the prior art.

[0013] Consequently, the applicant raised the technical question of how to produce, efficiently and economically, plastic-free bags for the transport of cement, glue and other similar materials, while being able to preserve the material they contain from moisture. Summary

[0014] The present utility model refers to a bag like the one indicated in claim 1.

[0015] Indeed, the applicant of this application has found, surprisingly, that the technical problem identified above can be solved efficiently and reliably by means of a bag made of at least two superimposed sheets of paper, in which:

[0016] - each of said outer sheet of paper and inner sheet of paper has a weight of 70 to 90 g / m2 and is of the semi-stretch type, i.e. it has a tensile strength in the machine direction MD of 6.4-7.8 kN / m and a tensile strength in the transverse direction TD of 4.7-5.8 kN / m, measured according to ISO 1924-3:2019

[0017] - each of said outer sheet of paper and inner sheet of paper is coated on one side of a vapor barrier layer with a weight of 10 to 20 g / m2, said weight being measured according to ISO 536:2019,

[0018] - said barrier layer comprises a polymer dispersion based on styrene and at least one pigment made of clay and calcium carbonate,

[0019] - said water vapor barrier layer is also coated with at least one water-based, wax-type hydrophobic paint coating, such as a polymer wax, comprising at least one element of the isothiazol-3-one type, for example 1,2-benzisothiazol-3(2H)-one, 5-chloro-2-methyl-2H-isothiazol-3-one (OMIT) and / or 2-methyl-2H-isothiazol-3-one, and mixtures thereof.

[0020] In this way, moisture / water vapor transmission (WVTR) and water absorption (COBB) are considerably reduced.

[0021] Indeed, thanks to the water vapor barrier layer and the hydrophobic paint layer applied to it, the water is not retained by the paper but slides off due to the high surface tension on the treated paper.

[0022] This results in a highly hydrophobic surface in the broadest sense of the term, indicating the property of not absorbing and not retaining water.

[0023] This increases the barrier effect compared to that which can be obtained by standard plastic bags known in the prior art, guaranteeing the product contained in the bag a high level of protection against moisture, even in the absence of intermediate polyethylene plastic sheets in the manufacture of the bag, thus improving the shelf life of the product contained in the bag.

[0024] In particular, the bag of the present utility model is found to be free of plastic elements (“plastic free”), while maintaining high preservation performance against moisture and water.

[0025] In addition, this gives the paper sheets constituting the bag an excellent smoothness characteristic of the Bentsen type, measured according to the UNI ISO 8791-2:2013 standard with values ​​ranging from 82 to 88 ml / min.

[0026] In the present description and in the accompanying claims, "bag" means a bag, pouch or any container or packaging of the type of roll packaging printable with inks and paints, intended for the safe transport and intact preservation of the materials contained therein, this material being solid, semi-solid or granular, of the different categories of products such as earth, sand, cement, plaster or other materials useful in the construction sector, as well as animal feed, seeds and food for people, or other materials useful in the food, chemical or transport sectors of minerals and similar products, this container being such that it can take the shape determined by the material contained therein in its entirety.

[0027] According to a preferred embodiment, said at least one layer of hydrophobic paint has a weight of 4-9 g / m2.

[0028] According to a preferred embodiment, said hydrophobic paint has a pH between 8 and 9.

[0029] According to a preferred embodiment, said hydrophobic paint has a relative density of about 1 g / cm3 at 20 °C.

[0030] According to a preferred embodiment, said hydrophobic paint has a viscosity < 2000 mPas, preferably < 1500 mPas.

[0031] According to a preferred manufacturing method, said paint is distributed on each of said sheets by the coating process, which is an industrial process involving the uniform application of said paint on said sheets, oven drying, possible calendering or embossing, and then subsequent cooling.

[0032] According to a preferred embodiment, said semi-stretchable type outer paper sheet has a tensile index in the machine direction MD of about 75 Nm / g according to ISO 1924-3:2019.

[0033] According to a preferred embodiment, said semi-stretchable type outer paper sheet has an elongation at break in the machine direction MD of about 5.2% and an elongation in the transverse direction TD of 9 to 9.5% according to ISO 1924-3:2019.

[0034] According to a preferred embodiment, each of said outer paper sheet and inner paper sheet is coated on one side with a water vapor barrier layer with a weight of approximately 15 g / m2.

[0035] This provides additional protection against water vapor.

[0036] According to a preferred embodiment, said barrier layer comprises a polymer dispersion comprising styrene-acrylate and / or styrene-butadiene.

[0037] According to a preferred embodiment, said barrier effect layer is applied to said outer sheet of paper and to said inner sheet of paper by means of a coating machine in offline mode.

[0038] According to a preferred embodiment, said coating machine is provided with a blade and an air dryer.

[0039] According to a preferred embodiment, said bag consists of a main lateral external surface and at least one lower base attached to said main lateral external surface, in which each of said lower base and of said main lateral external surface consists of at least two of said overlapping sheets of paper coated with at least one layer of hydrophobic paint.

[0040] In this way, the bag appears as if it were made of a single body.

[0041] Preferably, the consistency of the external lateral surface of the bag is such that it allows the bag to take the shape defined by the weight of the material it contains.

[0042] Preferably, said lower base has a flat, partially rigid surface so that it can serve as a base for the bag to rest on the ground. Thus, since the lower base is essentially flat, it is easier to place the bag on the ground on flat surfaces in a vertical position when the bag is full or partially full.

[0043] According to one embodiment, the bag preferably also consists of an upper base, essentially similar to the lower base; this allows the bag to be placed on the ground either using the lower base as a support on the ground, or, conversely, using the upper base as a support. This is particularly useful when the bag to be placed on the ground does not have a part that must necessarily face upwards and a part that must face downwards.

[0044] According to another embodiment, the bag of the present utility model is of the type defined as "open mouth," where there is no top base; the bag of this other embodiment is in fact presented with the upper part of the side surface open so that it can be easily filled. Once the bag is filled, this opening is closed using sealing machines.

[0045] According to a preferred embodiment, the inner sides of said at least two sheets are glued together at the upper end and the lower end of said sheets in order to create a kind of tube inside the bag.

[0046] According to a preferred embodiment, the inner sides of said at least two sheets are glued together at places located at said upper and lower ends.

[0047] According to a preferred embodiment, the inner sides of said at least two sheets are glued together with starch glue or vinyl glue.

[0048] Other features and advantages of the present utility model will be better understood from the following detailed description of preferred, but not exclusive, embodiments, illustrated by way of example only and without limitation. Detailed Description

[0049] The detailed description that follows refers to particular embodiments of the device of the present utility model, without limiting its content.

[0050] The bag of the present utility model is intended to contain cement or other similar materials useful in construction or in the food, mineral or chemical sectors, such as sand, gravel or other useful materials, for example, in the food and animal seed sector or similar products.

[0051] Example 1 (comparison).

[0052] A bag known in the prior art, hereinafter referred to as CFR1, consists of two overlapping sheets of paper, defined as an outer sheet and an inner sheet, free of plastic elements; the outer sheet is a semi-stretch paper sheet with a basis weight of 70 g / m² coated on one side with a water vapor barrier layer with a basis weight of 15 g / m², measured according to ISO 536:2019. The barrier layer comprises a styrene-based polymer dispersion and at least one pigment consisting of clay and calcium carbonate. This results in a total basis weight of 85 g / m². The structure of the outer sheet of the CFR1 comparison sample is therefore as follows:

[0053] water vapor barrier layer

[0054] semi-extensible outer paper sheet

[0055] Furthermore, the outer sheet has a tensile strength in the machine direction MD of 6.4 to 7.8 kN / m and a tensile strength in the transverse direction TD of 4.7 to 5.8 kN / m, and a tensile index in the machine direction MD of approximately 75 Nm / g according to ISO 1924-3:2019. The outer sheet also has an elongation at break in the machine direction MD of approximately 5.2% and an elongation in the transverse direction TD of 9 to 9.5%, also measured according to ISO 1924-3:2019. The outer sheet is superimposed on a standard semi-stretch inner sheet of paper (i.e., without the vapor barrier layer). The outer sheet has a width extending at least 20 mm beyond the width of the inner sheet to facilitate longitudinal gluing.

[0056] The CFR1 comparison bag has a main lateral external surface, a lower base, and an upper base attached to the main external surface, so as to form a single unit. The lower and upper bases have a partially rigid flat surface, so that it can be folded over the lateral surface when the bag is empty, allowing it to be stored in a minimal space, and so that it can serve as a base for the bag when it is at least partially filled and placed in an upright position.

[0057] Example 2 (comparison).

[0058] Another bag well known in the prior art (see Italian patent application no. IT 102020000013471 in the name of the same applicant as the present application), hereinafter referred to as CFR2, is similar to the comparison bag CFR1 above, the difference being that the comparison bag CFR2 is free of the water vapor barrier layer applied to the outer sheet. Instead, a hydrophobic, water-based polymer wax-type paint layer, with a basis weight of 5 g / m², a pH of approximately 8.5, and a relative density of of approximately 1 g / cm³ at 20 °C and a viscosity < 1500 mPas. The structure of the outer sheet of the CFR2 comparison sample is therefore as follows:

[0059] hydrophobic paint layer

[0060] semi-extensible outer paper sheet

[0061] Example 3 (utility model).

[0062] A bag of the present utility model, hereinafter referred to as INV1, comprises the same semi-stretchable outer paper sheet as that used in comparison examples CFR1 and CFR2, coated with the same water vapor barrier layer as that used in comparison example CFR1, with the addition on this layer of the same hydrophobic paint layer as that used in comparison example CFR2. The structure of the outer sheet of sample INV1 is therefore as follows:

[0063] hydrophobic paint layer

[0064] water vapor barrier layer

[0065] sheet of special semi-stretchable type paper

[0066] Test.

[0067] The CFR1 and CFR2 comparison bags and the INV 1 utility model bag were filled with cement or a similar material, as described above, and then sealed appropriately using traditional methods for filling and sealing these types of bags. For example, cement can be introduced into each bag through an opening in the bottom end, which is then automatically closed at the end of the bag filling phase by means of a special valve located on the bottom end. The bags, thus filled and sealed, were exposed to the elements for a period of 7 days, thereby simulating storage conditions for the finished product by an end user. The humidity to which the bags were exposed was ambient humidity.

[0068] Test 1: To determine the water absorption of the paper, the Cobb method described in the European standard EN ISO 535 was used, using three different contact times (60 seconds, 120 seconds, 300 seconds) and expressing the results in g / m2.

[0069] Test 2: To determine reliable values ​​for water vapor transmission (WVTR) through the paper sheets, the test method described in ASTM E96 / / E96M-15 procedure E was used, both under standard ambient conditions of 23°C and 50% relative humidity, and under extreme tropical conditions of 38°C and 90% relative humidity, expressing the results in g / m2 for 24 hours.

[0070] Table 1 below presents the results of the different tests.

[0071] [Tables 1] Sample Structure Test 1 60 sg / m² Test 1 120 sg / m² Test 1 300 sg / m² Test 2 2 3 °C 50% RH g / m² for 24 hours Test 2 38 °C 90% RH g / m² for 24 hours CFR1 (comparison) Semi-stretch paper + barrier layer 31.1 45.8 49.6 55 824-962 CFR2 (comparison) Semi-stretch paper + paint layer 4.7 5.5 5.6 115 735-757 INV1 (utility model) Semi-stretch paper + barrier layer + paint layer 10.1 11.4 12.3 15 255-292

[0072] Table 1 shows that the CFR2 comparison sample exhibited a water vapor transmission rate (WVTR) through the paper sheets of 115 g / m² over 24 hours under standard environmental conditions of 23 °C and 50% relative humidity (Test 2). Using the CFR1 comparison sample, this water vapor transmission rate was significantly improved, reduced to only 55 g / m² over 24 hours. However, using the CFR1 comparison sample, a significant deterioration (increase) in water absorption capacity was observed under all conditions of Test 1 (60 seconds, 120 seconds, and 300 seconds).

[0073] Surprisingly, the INV1 utility model sample showed a water vapor transmission value (WVTR) through the paper sheets of only 15 g / m² over 24 hours under standard ambient conditions of 23 °C and 50% relative humidity (test 2). This value is significantly lower than the figure obtained from the CFR1 comparison sample (going from 55 to 15 g / m² over 24 hours) and even lower than the figure obtained from the CFR2 comparison sample (going from 115 to 15 g / m² over 24 hours).

[0074] The value of 15 g / m2 for 24 hours obtained from the INV 1 sample of the utility model (which is free of plastic elements) was therefore extremely low, comparable to values ​​that can only be obtained with bags containing plastic elements, which are non-recyclable and therefore harmful to the environment.

[0075] Even under tropical conditions of 38°C and 90% relative humidity, the INV 1 utility model sample surprisingly showed a value water vapor transmission (WVTR) through the paper sheets considerably lower than figures obtained under the same conditions from the CFR1 and CFR2 comparison samples.

[0076] At the same time, the INV1 bag of the present utility model also showed acceptable values ​​regarding water absorption capacity in all conditions of test 1 (60 seconds, 120 seconds and 300 seconds).

[0077] Therefore, the bag of the present utility model, although free of intermediate plastic layers, offers excellent results in terms of moisture absorption due to its structure consisting of a semi-stretchable paper layer, onto which a water vapor barrier layer is applied, and onto which a hydrophobic paint layer is applied. Indeed, the aforementioned structure of the bag of the present utility model provided surprising synergistic results compared to the CFR1 and CFR2 comparison examples, where only the water vapor barrier layer (CFR1) or the hydrophobic paint layer (CFR2) was present on the semi-stretchable paper sheet. This results in a long shelf life for the product contained in the bag. Example 4 (utility model).

[0078] A bag of the present utility model, hereinafter referred to as INV2, has the same structure as the outer sheet of the INV1 bag of the present utility model seen above. The INV2 sample of the present utility model differs from the INV1 sample of the present utility model in that the same vapor barrier layer used in the structure of the outer sheet has also been applied to the semi-stretchable paper layer of the inner sheet.

[0079] The INV2 bag of the present utility model showed a water vapor transmission rate (WVTR) through the paper sheets of only 10 g / m² for 24 hours under standard environmental conditions of 23 °C and 50% relative humidity (test 2). This further reduces the value obtained with the same test using the INV1 bag of the present utility model, also by adding a water vapor barrier layer to the inner semi-stretch paper sheet.

[0080] Obviously, specialists in the field will be able to observe many modifications and variations of the preferred embodiments described above, while remaining within the framework of the present utility model.

[0081] For example, instead of using in the bag of the present utility model an outer sheet of semi-stretchable paper with a weight of 70 g / m2, it is possible to use weights of 80 and 90 g / m2, while retaining the weight of 15 g / m2 of the water vapor barrier layer applied to one side of this outer sheet, in order to obtain an overall structure of, respectively, 95 and 105 g / m2.

[0082] The side of the outer sheet where the vapor barrier layer is located is smoother than the opposite side of the outer sheet, giving the bag surface characteristics similar to those of coated paper. The smoother the surface, the higher the print quality.

[0083] Thus, the present utility model is not limited to the preferred embodiments described, illustrated for illustrative purposes only and without limitation, but is defined by the following claims.

Claims

Demands

1. A bag consisting of an outer paper sheet superimposed on an inner paper sheet, wherein: - each of said outer and inner paper sheets has a basis weight of 70 to 90 g / m² and is of the semi-stretch type, i.e., it has a tensile strength in the machine direction MD of 6.4-7.8 kN / m and a tensile strength in the transverse direction TD of 4.7-5.8 kN / m, measured according to ISO 1924-3:2019; - each of said outer and inner paper sheets is coated on one side with a vapor barrier layer having a basis weight of 10 to 20 g / m², said basis weight being measured according to ISO 536:2019; - said vapor barrier layer comprises a styrene-based polymer dispersion and at least one pigment consisting of clay and calcium carbonate,- said water vapor barrier layer is also coated with at least one water-based hydrophobic wax-type paint layer, such as a polymer wax, which comprises at least one element of the isothiazol-3-one type, for example 1,2-benzisothiazol-3(2H)-one, 5-chloro-2-methyl-2H-isothiazol-3-one (OMIT) and / or 2-methyl-2H-isothiazol-3-one, and mixtures thereof.

2. Bag according to claim 1, characterized in that said at least one layer of hydrophobic paint has a weight of 4 to 9 g / m2.

3. Bag according to any one of the preceding claims, wherein each of said outer paper sheet and inner paper sheet of semi-stretchable type has a tensile index in the machine direction MD of about 75 Nm / g according to ISO 1924-3:2019.

4. Bag according to any one of the preceding claims, wherein each of said outer paper sheet and inner paper sheet of semi-stretchable type has an elongation at break in the machine direction MD of about 5.2% and an elongation in the transverse direction TD of 9 to 9.5% according to ISO 1924-3:2019.

5. Bag according to any one of the preceding claims, wherein each of said outer paper sheet and paper sheet The internal layer is coated on one side with a vapor barrier layer with a weight of approximately 15 g / m2.

6. Bag according to any one of the preceding claims, wherein said polymer dispersion contains styrene-acrylate and / or styrene-butadiene.

7. Bag according to any one of the preceding claims, wherein said barrier layer is applied to said outer paper sheet and to said inner paper sheet by means of an offline coating machine.

8. Bag according to claim 7, wherein said coating machine is provided with a blade and an air dryer.

9. Bag according to any one of the preceding claims, consisting of a principal lateral external surface and at least one lower base attached to said principal lateral external surface, wherein each of said lower base and of said principal lateral external surface is made up of at least two of said overlapping inner and outer sheets of paper coated with at least one layer of hydrophobic paint.

10. Bag according to any one of the preceding claims, wherein said bag also consists of a top base fixed to said principal external surface, wherein said top base also consists of at least two of said overlapping inner and outer paper sheets coated with at least one layer of hydrophobic paint.