MXPA06005191A - Multi-layer wrapping material with water vapor-permeable inner layer - Google Patents

Abstract

A multi-layered sheet material for wrapping metal goods to protect them from corrosion during storage has a water impermeable and water vapor-impermeable outer layer comprising a coated woven scrim and a water-impermeable and water vapor permeable inner layer comprising a micro-perforated film. The inner layer incorporates corrosion inhibitors. The outer and inner layers are bonded along their longitudinal edges leaving a space between the layers into which water vapor can migrate away from the wrapped metal product.

Description

MULTILAYER MATERIAL FOR WRAPPING, WITH INTERNAL COATING PERMEABLE TO STEAM FIELD OF THE INVENTION The present invention is directed to the wrapping materials that are used to pack metal products. More specifically, it is directed to a multilayer laminate material that reduces corrosion of wrapped metal products during handling, transportation, storage.

BACKGROUND OF THE INVENTION Most metals are susceptible to corrosion under ambient or atmospheric conditions. The metal packaging industry has successfully created various methods and compounds to reduce the corrosion of metals during storage and use. However, the effectiveness of metal wrapping materials still requires improvements.

In the International Patent Publication WO 03/103957 Al dated December 18, 2003 (Shokar et al.), A laminated material having a thin, woven, outer canvas layer and an air impermeable inner film layer is disclosed. and to water and incorporates corrosion inhibitors. The two layers are joined along their edges, allowing each layer to move independently of the other, by sliding. It would be desirable, however, to provide a laminated wrapping material that allows water vapor or condensed water in contact with the wrapped metal article to migrate away from it.

SUMMARY OF THE INVENTION The invention provides a laminated material for wrapping metal articles, for example metal coils, to protect them from corrosion. This has a first layer, intended to be the outer layer during use, consisting of a thin fabric woven, coated, impervious to water and impervious to water vapor. It has a second layer, intended to be the inner layer of use, it is waterproof and permeable to water vapor and incorporates a corrosion inhibitor. The outer and inner layers are joined to each other. along two opposite edges, and as an option at other points, allowing the layers to slide one relative to the other and provide a space between the layers in which the water vapor can be drawn away from the surface of the wrapped metal article .

The water vapor permeability of the inner layer can be achieved by different means. In the preferred embodiment, the inner layer is micro-perforated. In other embodiments, the inner layer consists of a thermoplastic or polyurethane elastomer that is permeable to water vapor without perforations, for example, a film that can breathe water vapor. In still other embodiments, the inner layer is a biaxially oriented calcium carbonate film that has small holes around the calcium particles.

It will be understood that by describing a layer herein as "waterproof", it is understood that it is sufficiently impermeable for practical purposes as a wrapping material.

The polyester materials which are used for the first and second layers of the laminated material are preferably polyolefins, such as polyethylene or polypropylene, but may be any other that can be used in the field of industrial packaging, including polyesters, polyamides, PET and TPE In another embodiment of the invention, a layer of water absorbent material, for example a laminate of kraft paper, is attached to the inner side of the outer layer. The paper layer may incorporate a volatile corrosion inhibitor.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view through the laminate material according to the first embodiment of the invention.

Figure 2 is a cross-sectional view through the laminate according to the second embodiment of the invention.

Figure 3 is a cross-sectional view through the laminate according to the third embodiment of the invention.

DETAILED DESCRIPTION Figures 1 to 3 show preferred embodiments of the laminate. These drawings, the same or similar elements in the different modes are indicated by the same reference numbers. The figures are not to scale and accentuate the thickness of the different layers for clarity of the exemplification.

Figure 1 shows a first embodiment of the invention. The laminated material 2 consists of a thin coated canvas 4 and a polyolefin film 6 bonded along the opposite edges 30, 32 by strips of adhesive 8. During use to wrap metal products, the film 6 is the inner layer, that is, the layer that makes contact with the wrapped metal products, and the thin coated canvas 4 is the outer layer.

Since the layers 4 and 6 are joined together only on two opposite edges, preferably the edges parallel to the direction of the machine, and as an option at other points, but in any case not continuously along their surfaces, there are a space 10 between the two layers. It will be understood that, during use, the layers will touch at multiple points and the thickness of the space 10 at any point, i.e. the distance between layers 4 and 6, will vary and will largely depend on the way in which it is applied. Apply laminate 2 to a specific product.

The laminate material of the invention is produced by feeding the roller layers and through the traditional manufacturing equipment, including the rolling mills or rollers. The direction along the length of the material when processed through the production equipment is referred to herein as "machine direction". The direction perpendicular to the machine direction is referred to herein as the "transverse direction" with the direction being along the width of the laminate between the edges 30 and 32.

The thin canvas 4 is a woven structure made of polyolefin tapes that are manufactured by methods well known in the art. The tapes are preferably about 1.5 to 6 mm wide. The number of tapes in the direction of the machine is preferably in the intercalo of 4 to 16 tapes per inch. The number of tapes in the transverse direction preferably is the range of 2 to 16 tapes per inch. The decitex of the tapes (grams per 10,000 meters) are preferably in the range of 500-2500. The weight of the thin canvas preferably is in the range of 30 to 400 grams per square meter. The breadth of the thin sheet 4 and the sheet material 2 can be any convenient width that can be processed in available production equipment and that is suitable for a specific application. Preferably, it is in the range of 30 to 160 inches.

The thin canvas 4 has high mechanical and tensile strength in the machine and transverse directions. During the production of the tapes, these are normally stretched from 3 to 5 times their original length passing through hot rolls to align the polymer chains within the body of the tapes to increase their strength. It is a function of thin canvas to impart mechanical strength to the laminated material 2.

The thin sheet 4 can be made of any suitable polyolefin, including high density polyethylene, low density polyethylene and polypropylene.

The film 18 is laminated to the outer side of the thin canvas. The film 18 is a polyolefin coating applied to the thin canvas to make it impermeable to the transmission of water and water vapor, and practically impermeable to the passage of air. The thin coated canvas is therefore impermeable to water and impervious to water vapor, to protect the wrapped metal article. The thin coated canvas 4 may have a small degree of oxygen permeability to allow a small amount of air to pass through the laminate.

The layer 6 consists of a water impermeable film and permeable to water vapor. The peculiarity of water impermeability provides additional protection to that provided by the outer layer 4, 18 against the penetration of water into the wrapped metal object. The particularity of water vapor permeability provides means for water vapor that is close to the wrapped metal object to move away from it, as described below.

Preferably, layer 6 is a micro-perforated woven polyolefin envelope with a polyolefin coating on one side thereof. It can also be a polyolefin film, nonwoven, microperforated.

The microperforation of the laminate material to make it permeable to water vapor while retaining it impervious to water (i.e., impervious to liquid water) is well known in the art of manufacturing wrapping materials and is a commonly used process in the manufacture of the laminated material for homemade wraps. The layer 6 has a plurality of micro-perforations 14. Preferably, the water vapor permanence of the layer 6 is in the range of 170 to 1400 nanograms / Pa-s-m. The function of the micro-perforations 14 is to allow any condensation that may be present on the surface of the wrapped metal object, or between the layer 6 and the metal surface, to move it away from the metal surface through the micro-perforations in the form of steam, where it can be condensed on the inner surface of the outer layer 4, in the space 10, where it is far from direct contact with the metal surface.

To give the desired degree of water vapor permeability, those skilled in the art can choose different combinations of hole size and separation of the microperforations. An example of a suitable microperforated layer has perforations about 6 mm apart and with a hole diameter of about 0.22 mm. Preferably, the diameter of the perforations 14 is in the range of 0.005 mm to 0.35 mm.

The layer 6 is preferably made of polyolefin, for example polyethylene or polypropylene, with a thickness in the range of about 0.03 to 2 mm, more preferably about 0.1 mm.

Layer 6 incorporates a corrosion inhibitor to help prevent corrosion of the wrapped metallic object. -Preferably, it incorporates a volatile corrosion inhibitor and a contact corrosion inhibitor. If desired, you can incorporate one of these types of inhibitors to corrosion instead of both. Preferably, the volatile corrosion inhibitor is present in concentrations of 0.1 to 5% by weight (ie, relative to the weight of the inner layer). Preferably, the contact corrosion inhibitor is present in concentrations of 0.5 to 15% by weight. Volatile and contact corrosion inhibitors can be chosen from those known in the art. For example, the volatile corrosion inhibitor may be a nitrite compound such as dicyclohexylamine nitrite; The contact corrosion inhibitor can be potassium pyrophosphate or an alkali metal nitrite or benzoate, such as sodium nitrite or sodium benzoate. Any of a wide variety of volatile and contact corrosion inhibitors known in the art, and mixtures thereof, may be chosen for use in the invention. During use, volatile corrosion inhibitors are transferred to the metal surface by volatilizing from the solid phase and inhibit corrosion by forming a protective layer around the metal surface. The corrosion inhibitors by contact protect when going from the film to the metal surface. The laminated material can preferably provide corrosion inhibitors to the metal article for up to 2 years, effectively inhibiting corrosion.

The corrosion inhibitors are incorporated into the resin that is used to manufacture the film layer 6 by methods known in the art. Typically, the compositions are prepared with a carrier resin in a masterbatch, which is then mixed and diluted with the base resin that is used to prepare the film.

The thin coated canvas 4, being practically impermeable to gases, forms a barrier that holds any volatile corrosion inhibitor, released from the film 6 in the space 10 between the layers 4 and 6, so that it does not escape into the atmosphere. This volatile corrosion inhibitor can pass through the micro-perforations 14 and make contact with the wrapped metallic object.

The coated thin sheet 4 is bonded to the film 6 by adhesive strips 8 along the edges 30 and 32, that is, along the edges in the machine direction, the adhesive tapes are narrow in relation to the edges. with the total width of the laminated material. These are preferably in the range of 0.05-3 inches in width. The tapes 8 can be continuous or discontinuous. The layers may otherwise be joined by fusion bonding or sonic bonding, or other convenient means. The two layers of laminated material are therefore not joined except at their edges 30 and 32, and are free to slide relative to one another along the middle part and thereby operate independently from each other to protect the wrapped article. As an option, the additional gluing tapes or stitches for joining the layers 6 and 4 together can be provided, for example, to increase the mechanical stability of the laminated material 2 its amplitude is very large. In any case, the adhesion of layer 6 and 4 is not continuous along its surfaces. By not being laminated to the thin canvas, the inner layer is freer to join the wrapped metal product. The natural tendency of the polyolefin film to maintain a static charge favors the static union of the film to the metallic product. The close contact of the film 6 and the wrapped article leads to the transfer of the corrosion inhibitor by contact to the metal article.

Referring now to Figure 2, which shows a second embodiment of the invention, the laminate material 3 differs from the laminate material 2 in that it has a film 20 laminated to the inner side of the thin canvas 4. The film 20 is a polyolefin coating applied to the thin canvas to impart more protection against the passage of air and water in contact with the wrapped product. The film 20 preferably has 0.5 to 3 ils in thickness and has a weight of 12 to 72 grams per square meter. The polyolefin of film 20 can be any suitable polyolefin, such as high and low density polyethylene and polypropylene. It can be the same or different from the polyolefin of thin canvas 4 and film 18.

A third embodiment of the invention is shown in Figure 3. The laminate material 5 differs from the laminate material 2 in that it includes a layer of kraf5 paper 16 laminated to the inner side of the thin canvas 4. The kraft paper 16 preferably has a weight in the interval of 200 grams per square meter. This imparts moisture absorption capacity to the laminated material, whereby the water vapor that passes into the space 10 through the microperforations 14 and condenses in liquid water is absorbed into the paper layer 16.

In the third embodiment, the paper layer 16 or the layer 6 incorporate a corrosion inhibitor and, preferably, both layers incorporate it. When the paper layer 16 incorporates a volatile corrosion inhibitor, such a volatile corrosion inhibitor can pass through the layer 6 by its microperforations 14 and in contact with the wrapped metal article.

Although the invention has been described in terms of the specific embodiments, it is not intended that the invention be limited to these embodiments. Some modifications within the scope of the invention will be apparent to those skilled in the art. For example, instead of a layer of kraft paper, it is possible to use a layer of non-woven fibers. The inner layer can be made impermeable to water and permeable to water vapor by means other than microperforations. One or more layers may include pigments or other additives, such as flame retardants and compositions resistant to UV light, making the product more suitable for specific applications. The external surface can be treated with a non-slip coating. The scope of the invention is defined by the following claims.

Claims (18)

1. A laminated material for wrapping metal products consists of: (a) a first layer consists of a thin, woven, coated canvas; the thin coated canvas is impermeable to water and impervious to water vapor; (b) a second layer impermeable to water and permeable to water vapor and incorporating a corrosion inhibitor, the second layer being attached to the first layer in separate, narrow tapes, along two opposite edges of the first and second layers layers.

2. The laminated material according to claim 1, characterized in that the first layer further consists of a sheet of water absorbent material bonded to an inner side of the coated thin canvas.

3. The laminated material according to claim 2, characterized in that the absorbent material is kraft paper.

4. The laminated material according to claim 1, characterized in that the thin canvas consists of polyolefin ribbons.

5. The laminated material according to claim 4, characterized in that the polyolefin is polyethylene or polypropylene.

6. The laminated material according to claim 1, characterized in that the thin canvas is coated on one or both sides thereof with a polyolefin film.

7. The laminated material according to claim 1, characterized in that the first layer is joined to the second layer in narrow strips by means of an adhesive.

8. The laminate material according to claim 1, characterized in that the second layer has a water vapor permeation in the range of 170 to 1400 ng / Pa per second per square meter.

9. The laminated material according to claim 1, characterized in that the second layer is woven.

10. The laminated material according to claim 1, characterized in that the second layer is non-woven.

11. The laminated material according to claim 1, characterized in that the second layer has a thickness in the range of 0.3 to 3 mm.

12. The laminated material according to claim 1, characterized in that the corrosion inhibitor in the second layer comprises 0.5 to 5% by weight of the second layer.

13. The laminated material according to claim 1, characterized in that the second layer is micro-perforated.

14. The laminated material according to claim 13, characterized in that the microperforations have a diameter in the range of 0.005 mm to 0.35 mm.

15. A laminated material for wrapping metal products, comprises: (a) a first layer consists of a thin, woven, coated canvas; the thin woven canvas is impermeable to water and impervious to water vapor; (b) a second layer consisting of a film, the film being impermeable to water and permeable to water vapor (c) a third layer consisting of kraft paper bonded to one side of the first layer, the third layer being joined to the second layer in separate, narrow tapes, along two opposite edges of the third and second layers. (d) a corrosion inhibitor incorporated in at least the second or third layers or both.

16. The laminated material according to claim 15, characterized in that the corrosion inhibitor is incorporated in the second layer and includes a contact corrosion inhibitor.

17. The laminated material according to claim 15, characterized in that the corrosion inhibitor is incorporated in the third layer and includes a volatile corrosion inhibitor.

18. The laminated material according to claim 15, characterized in that the third layer is joined to the second layer in narrow strips by means of an adhesive.