ES2985430A1 - Paper with transparency properties, equipment and procedure for applying said properties to it (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Paper with transparency properties, equipment and method for applying said properties thereto, where the paper comprises a sheet of paper and a component that includes a wax and an additive formed by triglycerides that is integrated between the cellulose fibers. The equipment comprises an input surface with heating means, a first roller, a gun for applying the component, one or more knurled cylinders, a calender with at least two second rollers, and a third roller with cooling means. For its part, the method begins with the heating of the sheet on the input surface, subsequent movement of the sheet between a first roller and the gun, injection of the component by means of the gun and application of pressure by means of the knurled cylinder, followed by the movement of the sheet through the second rollers and the third cooled roller, and finally removal of the sheet. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Paper with transparency properties, equipment and procedure for applying said properties to it

Technical field of the invention

The present invention corresponds to the technical field of coating or packaging materials that are used to wrap products or to manufacture containers in which to contain them.

Background of the Invention

Nowadays, most products are packaged in one way or another. In the case of products that are not fresh, this packaging is usually more elaborate, but for fresh products, simpler packaging is used, such as a plastic bag or a paper bag, which allows for transport, protecting the product inside and maintaining its properties.

In the case of plastic bags or wrappers, in addition to the negative impact they generate on the environment, we must consider the disadvantages they pose for certain products, since they fail to maintain the qualities of the product to be preserved.

Paper, on the other hand, has multiple advantages, as it is biodegradable, reusable and, as it is also breathable, it eliminates microorganisms naturally through contact with oxygen.

Plastic is an impermeable material that does not allow the product inside to breathe, so the moisture in the product is retained and this causes it to become rubbery and unattractive. In addition, it is not resistant to temperature, so it is not suitable for certain products that are packaged hot. On the other hand, paper is breathable, but this can cause the product to lose its moisture too quickly and dry out.

To solve this problem, current technology is geared towards finding a way to obtain controlled, regulated paper transpiration by applying a degree of waterproofing that allows part of the product's humidity to be maintained in the right amount.

However, there is another characteristic that differentiates plastic and paper and that is not being taken into consideration, since plastic can have a quality, that of transparency, that paper does not have.

This is a problem because it is important for the consumer to be able to see the product contained in a package, in order to appreciate its characteristics. This applies to bags or any other type of packaging, because when they are made of plastic material they are transparent, but when they are made of paper this is not possible.

In the state of the art there are some ways to solve this problem by creating visibility spaces or windows, formed by portions of transparent plastic material, which are added to the paper, by means of adhesives or other means of joining and thus allow the inside of the bag to be visible through this window.

As an example of the state of the art, reference document ES2271096 can be mentioned.

This document ES2271096 defines a bag for wrapping food products, especially bread, rolls and snacks, made of a composite material with at least a first layer of cellulose material and a second layer of plastic. In addition, the composite material is perforated and the first layer of cellulose material is interrupted in at least one area to create an observation window.

This solution aims to control the breathability of the bag, using two layers, one of paper and one of plastic, with common holes. In addition, it also seeks to solve the problem of transparency in order to be able to see the product inside.

However, the main problem is not taken into consideration, which is the excessive use of plastic and the problems that this causes to our environment.

In other cases, the procedures to which the paper is subjected focus on applying a coating layer on one of the faces of the paper, trying to reduce its permeability to values suitable for good conservation of the product. However, they still do not solve the issue of the necessary transparency of these materials to correctly perform their packaging functions.

It is therefore necessary to find a way to solve this problem by obtaining a packaging material that is transparent and does not involve the use of plastics.

Description of the invention

The paper with transparency properties presented here comprises a sheet of paper made of cellulose fibres that has a Cobb absorption index of more than 28 gr/m2, a porosity of more than 300 ml/cm2, and a humidity of between 3 and 7%.

In addition, this paper contains a component consisting of a wax suitable for food use and an additive consisting of triglycerides in a proportion between 5 and 10% of the total weight of the component.

This component is absorbed by the paper sheet, such that it remains integrated between the cellulose fibers.

A device for applying transparency properties to a paper as defined previously is also presented, which comprises an input surface that has infrared heating means.

This equipment also has a first hot roller located after the inlet surface and a gun for applying the component. This gun is located above the first roller, such that between them they form a space capable of allowing the passage of the paper sheet.

The gun is connected to an injection pump and comprises a rod with a width equal to or greater than the width of the sheet, connected to a rotation motor.

This equipment also has one or more knurled cylinders coaxially connected to the rod and a calender formed by at least two second hot rollers arranged after the passage space, where both second rollers have a diameter such that the travel of the paper on them is greater than or equal to 3 m.

Finally, it features a third double roller with cooling means at a second temperature.

A procedure is also proposed for applying transparency properties to a paper using equipment such as those defined previously.

This procedure comprises a first phase consisting of applying a sheet of paper onto the input surface at a given speed.

The second phase consists of heating the sheet of paper to a first determined temperature, simultaneously with its movement over the input surface.

Next, a third phase of displacement of said sheet of paper is carried out through the passage space between the first roller and the gun for applying the component, where the rotation motor of the gun rod has a tangential speed equal to the speed of movement of the sheet.

The fourth phase consists of injecting the component using a gun onto the knurled cylinder, with a given flow rate and temperature, simultaneously with the movement of the sheet through the passage space.

Simultaneously with the rotation of the rod and the injection of the component, a fifth phase takes place, applying pressure on the surface of the paper sheet, by means of the knurled cylinder, such that it is capable of allowing the penetration of the component between the fibres of the sheet in a width of the sheet equal to or less than that of the knurled cylinder.

A sixth phase is then carried out, involving the movement of the sheet of paper along a length greater than or equal to 3 m through the calender with two second hot rollers, where these second rollers have a tangential speed equal to the movement speed of the sheet of paper.

Finally, a seventh phase takes place, the paper sheet is moved over a third double roller which has a second temperature for cooling, and an eighth phase takes place for the removal of the sheet.

The paper with transparency properties proposed here provides a significant improvement on the state of the art.

This is because a material is obtained whose optical properties can be modified, either in one area of it or in its entirety.

The aim of this material is not to waterproof it or make it attractive to the eye through a shiny or satiny optical effect, but rather to provide it with transparency properties that allow the product contained inside to be distinguished, once it is packaged with this material.

This material with the component integrated inside is suitable for food use and can be used in the production of bags, containers, container lids, etc.

Furthermore, this component can be applied to the entire sheet of paper, to a strip of it, or to separate areas of the sheet, depending on the interest and the use to be given to said sheet. For example, in the case of bags for transporting loaves of bread, a longitudinal strip can be made in the sheet of paper, which will allow perfect visual access to the inside of the bag.

It is a completely recyclable material, as transparency is achieved without having to add any plastic. Nor is any other material added, as what is done is the alteration of the structural composition of all or part of the sheet, but it is still a sheet without pieces or materials attached, so it is more resistant and does not present the problem of separation or breakage of the joints between materials.

Furthermore, since the component is integrated into the interior of the paper, between its own fibres, it does not result in an oily finish, as it is not applied superficially but at a structural level.

The procedure applied with the appropriate equipment allows the penetration of the component between the fibers of the paper sheet, achieving an integration of the component in the paper and not a coating of one side of it.

It is therefore a very effective paper that has transparency properties without the use of plastics or derivatives, so it is 100% recyclable.

Brief description of the drawings

In order to assist in a better understanding of the characteristics of the invention, in accordance with a preferred example of its practical implementation, a series of drawings is provided as an integral part of said description, where, for illustrative and non-limiting purposes, the following has been represented:

Figure 1.- Shows a perspective view of the equipment for applying transparency properties to a paper, for a first preferred embodiment of the invention.

Figure 2.- Shows a profile view of the equipment for applying transparency properties to a paper, for a first preferred embodiment of the invention.

Figure 3.- Shows a perspective view of a paper with transparency properties obtained using the equipment, for a first preferred embodiment of the invention.

Figure 4.- Shows a perspective view of a paper with transparency properties obtained using the equipment, for a second preferred embodiment of the invention.

Detailed description of a preferred embodiment of the invention

In view of the figures provided, it can be observed how in a first preferred embodiment of the invention, the paper with transparency properties, proposed here, comprises a sheet (1) of paper formed by cellulose fibers that has a Cobb absorption index whose value is greater than 28 gr/m2, a porosity with a value greater than 300 ml/cm2, and a humidity between 3 and 7%.

It also includes a component consisting of a wax suitable for food use and an additive consisting of triglycerides in a proportion between 5 and 10% of the total weight of the component.

This component is absorbed by the paper sheet (1), such that it remains integrated between the cellulose fibers, therefore, a compound is sought that has a high penetration power in the paper sheet.

Therefore, a sheet (1) of paper with a high absorption capacity is sought that is capable of absorbing the component in its structure. Until now, in the sheets of paper that were worked with, the opposite was sought, that is, the lowest possible absorption capacity, because, the greater the absorption capacity, the more water the fibers have and this makes them less resistant and, in addition, the greater the absorption, the greater the consumption of products of the final finishing of the paper, such as glues, inks...

In the case of this invention and the objective pursued, it must be taken into account that the transparency of the paper is achieved when the rays of light pass through the labyrinth of fibers and air that make up the sheet of paper and manage to escape from it.

The structure of paper fibre is made up of an amalgam of cellulose fibres of different sizes, bleaching agents, sizing agents and fillers, so the aim of this invention is to ensure that light can pass through this structure as easily as possible. This is achieved by reducing the difference between the refractive index of the cellulose fibres and the air surrounding them. If the gaps between the fibres, occupied by air, are filled with a component with a refractive index more similar to that of cellulose than to that of air, the desired objective is achieved.

The degree of absorption of a cellulose paper depends on three factors: the Cobb index, which is a parameter used to measure the capacity of the paper to absorb water or any other type of liquid; the porosity, which is the relationship between the volume occupied by air in a paper and the total volume; and; the humidity.

Humidity is directly related to the ability to absorb other elements. The less humidity, the greater the capacity and the higher the Cobb index.

Thus, depending on these variables, different transparency results are obtained.

In this first preferred embodiment of the invention, the paper sheet (1) has a weight of 32 gr/m2 and the Cobb absorption index has a value greater than 28 gr/m2 and the porosity has a value greater than 300 ml/cm2.

In another embodiment, the paper sheet (1) has a weight of 35 gr/m2 and the Cobb absorption index has a value greater than 32 gr/m2 and the porosity has a value greater than 350 ml/cm2.

On the other hand, in another preferred embodiment, the paper sheet (1) has a weight of 40 gr/m2 and the Cobb absorption index has a value greater than 35 gr/m2 and the porosity has a value greater than 400 ml/cm2.

As already indicated, on the one hand, the sheet (1) of paper must be as absorbent as possible in order to be able to fill the gaps with a component that must have a refractive index that is as similar as possible to the refractive index of cellulose.

In this first preferred embodiment of the invention, the component comprises a wax formed by at least one vegetable wax. In other embodiments, the wax is formed by at least one paraffin.

Furthermore, in this first preferred embodiment, the triglycerides are formed by a mixture of palmitic acid and linoleic acid.

Vegetable waxes are used in the component, but from a thermodynamic point of view they have no affinity with the cellulose of the paper. That is why an additive such as the aforementioned vegetable oils is used.

The aim is to convert the polarity of the cellulose into apolar one, thus creating an affinity with the vegetable wax. This is achieved by mixing the vegetable wax with the triglycerides.

These long-chain triglycerides, such as palmitic acid and linoleic acid, make the vegetable wax non-polar, which makes it easier to create bonds between the cellulose and the vegetable wax.

In this first preferred embodiment of the invention, the transparency properties are in at least one area of the sheet of paper, which in this case is a band (2) of the sheet (1), as shown in Figure 2. In other preferred embodiments, the transparency properties are in the entire sheet (1) of paper.

It may also occur as shown in Figure 3, which represents the result obtained with a paper in which the transparency properties are in several areas of the paper sheet (1), which may be two or more continuous bands, or as in this second preferred embodiment, two discontinuous bands (2), that is, formed by portions aligned and separated from each other.

This paper also proposes equipment for applying transparency properties to a paper as defined previously.

As shown in Figures 1 and 2, this equipment comprises an input surface (3) presenting infrared heating means (4).

It also has a first hot roller (5) located next to the entry surface (3) and a gun (6) for applying the component.

This gun (6) is located on the first roller (5), such that between them they form a space capable of allowing the passage of the sheet (1) of paper. The gun (6) is connected to an injection pump and has an inlet (6.1) for the component from the pump. It also comprises a rod (7) with a width equal to or greater than the width of the sheet (1), connected to a rotation motor (not shown in the Figures).

The equipment has one or more knurled cylinders (8) coaxially connected to the rod (7). In the first proposed embodiment, as shown in Figure 3, it comprises a knurled cylinder (8), to generate a band (2) with transparency properties in the sheet (1), while, as can be seen in Figure 4, in a second embodiment, the equipment has two knurled cylinders (8) and with them two bands (2) with transparency properties are obtained, which in this case are discontinuous, but in other cases they can be continuous.

As shown in Figures 1 to 3, the equipment also comprises a calender formed by at least two second hot rollers (9) arranged after the passage space (11), and a third double roller (10) arranged after the calender, which has cooling means at a second temperature.

In this first preferred embodiment of the invention, the gun (6) comprises a reducing element for its application nozzle.

Likewise, in this first embodiment, the gun (6) comprises an encoder for the application of the component by means of pulses in a discontinuous manner when necessary. With an encoder, a sheet (1) can be obtained as shown in Figure 4, for a second embodiment, with discontinuous bands (2).

Likewise, in this case the gun (6) includes a photocell.

This paper also presents a procedure for applying transparency properties to a paper as defined and with the equipment described above.

This procedure comprises a first phase consisting of applying a sheet (1) of paper onto the input surface (3) at a given speed.

A second phase consists of heating the sheet (1) of paper to a first determined temperature, simultaneously with its movement on the input surface (3).

In this first preferred embodiment of the invention, the first application temperature of the component is between 100 and 110°. By heating the paper sheet (1), its humidity is reduced to an amount of 5%.

The third phase consists of a movement of the paper sheet (1) through the space (11) between the first roller (5) and the gun (6) for applying the component. The rod rotation motor (7) has a tangential speed equal to the movement speed of the sheet (1).

Next, a fourth phase of injection of the component takes place by means of the gun (6) on one or more knurled cylinders (8), with a determined flow rate and temperature, simultaneously with the movement of the sheet (1) through the passage space (11).

In this first preferred embodiment of the invention, the application temperature of the component is equal to the first temperature. In this way, the existence of thermal shock between the sheet (1) of paper and the component is avoided at the moment in which it is deposited on it and, therefore, the liquid phase of the component is not interrupted, facilitating its penetration into the structure of the sheet (1) of paper.

The fifth phase consists of applying pressure on the surface of the paper sheet (1) by means of the knurled cylinder (8) simultaneously with the rotation of the rod (7) and the injection of the component, such that it is capable of allowing the penetration of the component between the fibres of the sheet (1) in a width equal to or less than that of the knurled cylinder (8).

The knurling of the cylinder is what actually introduces and puts the component into contact with the sheet of paper (1). This knurling must have sufficient capacity to not cause an opening of the application band (2).

The knurling of the rod (7) varies depending on the component input we need, so that the higher the paper weight, the greater the input needed. This knurling also depends on another factor, such as the working speed.

Thus, the higher the working speed, the greater the opening of the engraved cell is required for knurling. In this first preferred embodiment of the invention, the speed of movement of the paper sheet (1) is 40 m/min and a knurling with a 120° opening cut is sufficient for the component to emerge completely from the cell.

In other embodiments with speeds of 60 m/min, a cell opening angle of 130° is required, while for speeds of 100 m/min, the cell opening must be 140°.

The knurled cylinder (8) receives the component delivered by the gun nozzle (6) and deposits it under pressure on the sheet (1) of paper, pressing against the first roller (5) which in this first embodiment is formed by a high-hardness rubber roller. In this way, the component is forced into the interior of the sheet (1) of paper by pressure.

As already indicated, the speed of the rod (7) and the paper sheet (1) is the same. This ensures that the component applied to the knurled cylinder (8) is transferred to the paper without any build-up or drag.

The rod (7) is connected to a motor that provides the turning movement. This motor is connected to a variable speed drive that receives information on the speed of the material from the same tachometer as the pump.

In this way we ensure that the rod nozzle (7) is synchronized to the speed of the paper, as well as the pump drive. Both the pump and rod mechanisms receive information on the speed of passage of the paper sheet (1) from the same tachometer and both have to be perfectly synchronized.

The sixth phase of this procedure consists of a movement of the sheet (1) of paper for a time greater than or equal to 3 minutes, through the calender, where the second rollers (9) have a tangential speed equal to the speed of movement of the sheet (1) of paper.

This minimum time of 3 min at high temperature allows the component to completely penetrate the structure of the paper sheet (1).

A seventh phase consists of a displacement of the paper sheet (1) on a third double roller (10) which has a second temperature for cooling. This drop in temperature causes the component to cool inside the structure of the paper sheet (1) and thus become integrated into it.

Finally, an eighth and final phase consists of removing the sheet (1).

In this first preferred embodiment of the invention, as shown in Figure 3, the application of the component is carried out on a band (2) on the sheet (1) of paper and this band (2) has a width equal to the width of a reducing element of the application nozzle of the gun (6).

In a second preferred embodiment, the component application is carried out discontinuously on the paper sheet (1) according to the pulses generated by an encoder of the gun (6), as can be seen in Figure 4.

In other preferred embodiments of the invention, the sheet (1) of paper comprises at least one print on its surface and the injection of component onto the knurled cylinder (8) comprises an initial reading stage by means of a photocell of the gun (6) connected to the pump to determine the existence or absence of printing on the sheet (1) such that the pump is capable of stopping the injection of the gun (6) when it detects a print and activating it when it detects the absence of printing.

Claims (1)

1- Paper with transparency properties, characterized in that it comprises a sheet (1) of paper formed by cellulose fibers that has a Cobb absorption index whose value is greater than 28 gr/m2, a porosity with a value greater than 300 ml/cm2, and a humidity between 3 and 7% and, a component that comprises a wax suitable for food use and an additive formed by triglycerides in a proportion between 5 and 10% with respect to the total weight of the component, where this component is absorbed by the sheet of paper, such that it remains integrated between the cellulose fibers. 2- Paper according to claim 1, wherein the wax is formed by at least one vegetable wax. 3- Paper according to claim 1, wherein the wax is formed by at least one paraffin. 4- Paper according to any of the preceding claims, wherein the triglycerides are formed by a mixture of palmitic acid and linoleic acid. 5- Paper according to any of the preceding claims, wherein the paper sheet (1) has a weight of 32 gr/m2 and the Cobb absorption index has a value greater than 28 gr/m2 and the porosity has a value greater than 300 ml/cm2. 6- Paper according to any of claims 1 to 4, wherein the paper sheet (1) has a weight of 35 gr/m2 and the Cobb absorption index has a value greater than 32 gr/m2 and the porosity has a value greater than 350 ml/cm2. 7- Paper according to any of claims 1 to 4, wherein the paper sheet (1) has a weight of 40 gr/m2 and the Cobb absorption index has a value greater than 35 gr/m2 and the porosity has a value greater than 400 ml/cm2. 8- Paper according to any of the preceding claims, wherein the transparency properties are in at least one area of the paper sheet (1). 9- Equipment for applying transparency properties to a paper, as defined in claims 1 to 8, characterized in that it comprises - an input surface (3) having infrared heating means (4); - a first hot roller (5) located next to the inlet surface (3); - a gun (6) for applying the component located on the first roller (5), such that between them they form a space (11) capable of allowing the passage of the sheet (1) of paper, where the gun (6) is connected to an injection pump and comprises a rod (7) of width equal to or greater than the width of the sheet (1), connected to a rotation motor; - one or more knurled cylinders (8) coaxially connected to the rod (7); - a calender formed by at least two second hot rollers (9) arranged after the passage space (11), where both second rollers (9) have a diameter such that the travel of the paper on them is greater than or equal to 3 m, and; - a third double roller (10) arranged after the calender, which has cooling means at a second temperature. 10- Equipment according to claim 9, wherein the gun (6) has a reducing element for its application nozzle. 11- Equipment according to any of claims 9 or 10, wherein the gun (6) comprises an encoder for applying the component by means of pulses in a discontinuous manner. 12- Equipment according to any of claims 9 to 11, wherein the gun (6) comprises a photocell. 13- Procedure for applying transparency properties to a paper as defined in claims 1 to 8, by means of equipment as defined in claims 9 to 12, characterized in that it comprises - a supply of a sheet (1) of paper onto the inlet surface (3) at a given speed; - heating the paper sheet (1) to a first determined temperature, simultaneously with its movement on the input surface (3); - a displacement of said sheet (1) of paper through the passage space (11) between the first roller (5) and the gun (6) for applying the component, where the rotation motor of the rod (7) of the gun has a tangential speed equal to the displacement speed of the sheet (1); - an injection of the component by means of the gun (6) onto one or more knurled cylinders (8), with a determined flow rate and temperature, simultaneously with the movement of the sheet (1) through the passage space (11); - an application of pressure on the surface of the paper sheet (1), by means of the knurled cylinder (8) simultaneously with the rotation of the rod (7) and the injection of the component, such that it is likely to allow the penetration of the component between the fibres of the sheet (1) in a width equal to or less than that of the knurled cylinder (8); - a displacement of the paper sheet (1) along a length greater than or equal to 3 m through the calender with two second rollers (9), where these second rollers (9) have a tangential speed equal to the displacement speed of the paper sheet (1); - a displacement of the paper sheet (1) on a third double roller (10) presenting a second temperature for cooling, and; - a removal of the sheet (1). 14- Method according to claim 13, wherein the application temperature of the component is equal to the first temperature. 15- Method according to any of claims 13 or 14, wherein the application of the component is carried out on a band (2) on the sheet (1) of paper and the band (2) has a width equal to the width of a reducing element of the application nozzle of the gun (6). 16- Method according to any of claims 13 or 14, wherein the application of the component is carried out discontinuously on the sheet of paper according to the impulses generated by an encoder of the gun (6). 17. Method according to any of claims 13 or 14, wherein the sheet (1) of paper comprises at least one print on its surface and the injection of component onto the knurled cylinder (8) comprises an initial reading stage by means of a photocell of the gun (6) connected to the pump to determine the existence or absence of printing on the sheet (1) such that the pump is capable of stopping the injection of the gun (6) when it detects a print and activating it when it detects the absence of printing. 18- Method according to any of claims 13 to 17, wherein the first application temperature of the component is between 100 and 110°.