IT202200026532A1 - PAPER PRODUCTION MIXTURE, ESPECIALLY FOR RECYCLED PAPER AND ITS MANUFACTURING PROCEDURE - Google Patents

Description

DESCRIPTION

Attached to a patent application for an INDUSTRIAL INVENTION having as its title

?PAPER PRODUCTION MIXTURE, PARTICULARLY FOR RECYCLED PAPER AND ITS MANUFACTURING PROCEDURE?

The present invention relates to a mixture, in particular for an additive mixture for the production of paper, particularly for recycled paper, even more particularly in the production of paper made with "poor" fibres, and its manufacturing process. The invention also concerns a sheet of paper made with the aforementioned mixture as well as a method for producing a sheet of recycled paper.

Environmental issues now involve all production sectors and there is an ever-increasing need to produce with a strongly limited ecological impact and to be part of the so-called circular economy.

In the paper sector in particular, recycled paper has been used for years in civil and industrial settings, for example in writing and printing, in packaging, in the production of corrugated cardboard or for paper used for sacks and bags.

These are products of universal use, with increasing production and demand rates, whose use has a strong and widespread production of waste.

As is known, paper is a recyclable material, since the cellulose it contains can be subjected to repeated processing cycles. The recovered paper can be treated and reused as secondary material for the production of new paper.

In fact, a large part of the paper waste fiber is transformed into new paper, guaranteeing great energy, water and wood savings.

The transformation of waste paper into raw material occurs in various phases:

? collection and storage;

? selection, to separate the fibres usable with the different types of waste paper;

? pressing and tying into bales (the latter, sent to the paper mills, undergo the actual recycling process);

? shredding;

? bleaching to remove inks (decolorization);

? reduction to pulp with the addition of hot water;

? refinement (impurities and waste are removed from the mixture until the cellulose pulp is separated);

? addition of virgin cellulose, in different proportions depending on future use.

At this point in the cycle, the cellulose contained in the waste paper has returned to being a raw material ready to re-enter the production cycle. Since with each reuse cycle there is a loss of resistance, it is known to insert refined fibers that can provide support to the product that comes out of the paper mill.

To this end, research is being carried out to find alternative annual fibres that, with appropriate processing, allow their use in paper production.

These fibres, suitably refined, are the basis of a mixture that is combined with typical mixtures from the paper sector made with poor cellulose (recycled paper or short fibres).

The industrial use of other materials obtained from agricultural production waste is already known: hemp, beans, apples, coffee, oranges and even seaweed (see biomela paper, favini seaweed paper, etc.).

These fibres, however, even if they can be integrated very well into the paper, do not add technical characteristics, rather they reduce them and are used only as recovery and filler.

Cellulose fibers use hydrogen bonds between fibrils to form paper sheets; in various ways, including refining, we try to create cell walls with as many fibrils as possible.

At the current state of the art, the refinement of the fibers is increased in order to have, at least initially, an increase in resistance. However, beyond a certain limit, the fibers become too small and the resistance of the sheet decreases.

Therefore, a thorough refining is never carried out precisely so as not to have the opposite effect that is sought, that is, to confer mechanical resistance to the paper produced.

There are alternatives to refining cellulose fibers in the paper industry to strengthen the bonds between the fibers, such as process aid chemicals, enzyme processing of the cellulose fibers to obtain a fiber with cell walls with many fibrils, or reducing the cellulose fibers to the level of microfibrils (MCF) and/or nanocellulose (CNF): by processes (high pressure and temperature homogenizers, cryogenic crushing, ultrasound, electrospinning and even grinding) that burst the cellulose fibers and then split their cell walls producing many fibrils.

The aim of the invention is to eliminate the above-mentioned drawbacks in known types of pulp for the production of paper, particularly recycled paper, and to create a pulp based on eco-sustainable alternative annual fibres that can be added to paper mill pulps with the aim of increasing their performance.

Within the scope of the above-mentioned task, an object of the invention is to provide a mixture for the production of paper, particularly recycled paper, which is also compatible with the paper recycling process currently used.

Another purpose of the invention is to produce the dough with means that are easily available on the market and using commonly used materials, so that the device is economically competitive.

This aim, as well as these and other objects which will become clearer hereinafter, are achieved by a pulp for the production of paper, particularly recycled paper, and its manufacturing process, according to the invention, comprising the technical characteristics set forth in one or more of the accompanying claims. The dependent claims correspond to possible different embodiments of the invention.

In particular, in accordance with a first aspect, the present invention concerns a mixture 1 for the production of paper, particularly recycled paper, which comprises hemp fibres, preferably cannabis sativa, which have a statistical average length and a statistical average width such that:

the average length is less than or equal to substantially 0.6 mm, preferably less than or equal to substantially 0.5 mm; and

the average width is substantially between 10 and 20 ?m, extremes included, preferably substantially between 12 and 18 ?m, extremes included.

Normally, the statistical mean length and statistical mean width are understood to be carried out with the pure statistical mean, not weighted according to other coefficients.

Hemp fibres, particularly from Cannabis sativa, had already found wide use in the production of paper.

However, nowadays, after different types of treatment (chemical, thermomechanical, maceration with or without enzymes, combined treatments, etc.), it is possible to obtain fibres of a length suitable for the production of sheets of paper, that is, fibres with a statistical average length of 1.5 mm (distributed in a length spectrum between 0.2 and 7 mm) and a statistical average width between 15 and 25 ?m. These fibres can subsequently be refined to improve their characteristics and obtain pulps with a ?drainability? index of 30-60 according to the Schopper-Riegler model, to produce a sheet of paper.

These fibres are then used to produce paper either in percentages of 100% or in variable percentages mixed with other cellulose fibres.

The Applicant has perceived that, contrary to the technological prejudice according to which by pushing the refining beyond a certain limit, the fibres become too small and the sheet resistances decrease, by producing a mixture with even smaller fibres, fibres are still obtained which improve the mechanical qualities so much so that, in laboratory analyses, sheets made with the Rapid Kothen system using 100% of this type of mixture have a high density (about 0.9 g/cm?), a high resistance to air permeability (Gurley >15 minutes), a tensile index greater than 60 N*m/g and a burst index greater than 3.5 KPa*m?/g.

Another aspect of the invention is given by the process for the production of a mixture, particularly an additive mixture, for the production of paper, particularly recycled paper, containing hemp fibres, preferably cannabis sativa, which comprises the phases consisting of:

- soak the hemp fibres in a first container containing water, with a concentration substantially between 3 and 5% of the dry weight, at a temperature preferably between 20 and 40 °C for a period substantially between 12 and 24 hours, in order to promote the imbibition of said macerated hemp fibres;

- pulp the soaked hemp fibres, gradually placing them in a refiner and diluting them with water to obtain a mixture with a concentration substantially between 0.5 and 2%, for substantially 20-30 minutes;

- circulate the mixture of fibres to be pulped in a closed circuit, inside the refiner without applying pressure, so as to progressively increase the density of said fibres to be pulped, until adequate homogenisation is achieved in the refiner circuit and until the first container is completely emptied;

- refine the fibres thus obtained in a cyclical manner in a closed circuit, progressively applying pressure to the roller (or rollers depending on whether the refiner is of the roller/flat or roller/roller or multi-roller type) of the refiner, until a pressure substantially equal to at least a value of at least 150 KPa is reached;

- purify the refined mixture from any coarse residues using a mechanical filter with fine slots and collect this mixture in a second container.

The Applicant had the intuition to start the process, which is the object of this patent application, from the hemp fibres obtained by maceration and subsequent beating processes: these macerated fibres are still very long and unusable for the production of paper, but, although very weakened, they are advantageously rich in cellulose, low in ash and lignin content and can be further easily worked without the addition of chemical agents.

Advantageously, these fibres, which are subjected to a mechanical refining process in water (temperature 20-40?C) with a mechanical pressure technique between two rollers or between a roller and a plate (depending on the refiner used), to carry out a grinding, cutting and opening process in order to reduce their size, further defiber them and allow the individual fibres to form short, thin, filamentous fibres, reduced to small and flattened (?fine?) particles, have many more bonds with the other fibres normally used for paper.

Another aspect of the invention is given by the creation of a sheet of paper made with a mixture as described and object of the invention. Last but not least, a further aspect of protection requested concerns a method of production of a sheet of paper, particularly recycled paper, which comprises the addition of the mixture of hemp fibres, preferably of cannabis sativa, according to the invention, to a traditional mixture of cellulose, preferably of poor cellulose.

In this case, the Applicant, having understood that due to the high flowability value it would not be possible to produce sheets of paper with 100% of this mixture, advantageously thought of adding this mixture which is the subject of the patent to other mixtures consisting of cellulose fibres typical of paper production, in a percentage substantially between 2 and 30% of the dry weight.

Further features and advantages of the invention will become clearer from the description of a preferred but not exclusive embodiment of the mixture for the production of paper, particularly recycled paper, illustrated by way of example and not in a limiting manner with the aid of the attached drawings in which:

Figure 1 schematically illustrates the process for producing a mixture 1 as an additive for the production of paper, particularly recycled paper, containing hemp fibres which are the subject of the invention;

Figure 2 schematically illustrates the application of refining in refiner 3 with a mechanical maceration system between a single roller (31) and its relative surface (32).

With reference to the above figures, a preferred embodiment of a mixture 1 additive for the production of paper, particularly recycled paper, and its manufacturing process is shown, which comprises a fibre from an annual plant of Cannabis sativa which, after appropriate processing, allows for the production of very short fibres rich in fibrils, which, added in a minimal percentage, in the production of paper allows for a notable increase in performance by increasing the strength of the bonds between the fibres, or the resistance, especially in papers made with normally weak fibres (short fibres, fibres from recycled paper).

Fibrils from hemp fibres, i.e. very short fibres and bundles of filaments, obtained from specific processing, which are characterised as mixture 1 statistically constituted by fibres with a statistical average length L(n) <0.5 mm; of which:

? approximately 50% of fibres with length L(n) < 0.2 mm

? approximately 40% of fibres have length L(n) between 0.2 and 0.5 mm

? 1-5% residue of fibres with length L(n) >1mm,

? statistical mean width W(n) = 10-20 ?m.

Furthermore, dough 1 has a ?dryness? ?SR >90.

Any laboratory-produced paper sheets, made with the Rapid Kothen system using 100% of this type of pulp 1, have a high density (about 0.9 g/cm?), a high resistance to Gurley air permeability >15 minutes, a high tensile index > 60 N*m/g and a high burst index > 3.5 kPa*m?/g.

To produce a mixture 1 for the production of paper, particularly recycled paper, containing hemp fibres, one starts from cannabis sativa fibres obtained by maceration and subsequent beating processes, etc. which are not the subject of this invention.

The retted hemp fibres, however, are still very long and unusable for the production of paper; although they are very weakened, they are still rich in cellulose, have a low ash and lignin content and can therefore be easily further processed without adding chemical agents.

The process, according to the invention, starts from these fibres which are subjected to a mechanical refining process in water at a temperature of approximately 20-40?C, with a mechanical pressure technique of the flow F of fibres between a roller 31 and a plane 32 (figure 2) - or between two opposing rollers -, in order to carry out a grinding, cutting and opening type of processing. In this way, the fibres are reduced in size, more frayed and each of these short, thin and filamentous fibres (?fine?), thus produced, is reduced to a small crushed particle which can form many more bonds with the other fibres normally used for paper.

Processing is carried out in the so-called ?batch? mode, that is, in successive batches of fibres which are processed by passing from a first container 2 to a second container 5, by means of pipes 7 and pumping means 6, after having been processed in a refiner 3, for example the industrial-type Valley refiner.

With reference to figure 1, the phases and characteristic data of the processing are described in the following way.

First, there is a soaking phase with water (T= 20-40?C) in the first container 2, for imbibition of the macerated hemp fibres with a concentration of 3-5%. The soaking lasts from 12 to 24 hours.

Then there is a pulping phase: the soaked fibres contained in the container 2 are progressively inserted, by means of motor means 6, into the refiner 3, adding dilution water to obtain a mixture with a concentration of 0.5-2%.

In this phase, which lasts about 20-30 minutes, the fiber mixture is circulated in a closed circuit and the roller 31 of the refiner 3 does not exert pressure. The fiber is circulated by progressively increasing its density until adequate homogenization is obtained in the refiner circuit and until the first container 2 is completely empty.

The temperature of the dough can preferably be maintained between 20-40?C.

Soaking is followed by refining which occurs cyclically in a closed circuit in which the mixture to be refined circulates. Between roller 31 and plate 32, crossed by the flow F of fibres, pressure is progressively applied until pressures of 150-300 kPa and above are reached.

Advantageously, the roller 31 (or rollers in the case of a roller/roller or multi-roller refiner) is equipped with rectangular blades/teeth with rounded, non-sharp edges, which come into contact with a smooth or contoured surface, or other blades/teeth with the purpose of compressing the fibres between the two surfaces (fig.2).

Subsequently, the refining phase is expected to be controlled by performing flow measurements according to the Schopper-Riegler measurement model (?SR), until a predefined value is reached. This predefined value corresponds in the example described here to ?SR >90. Once the predefined value is exceeded, a further check is carried out on the statistical mean length and the refining continues until a refined dough is reached with fibres of statistical mean length L(n)<0.5 mm and approximately 95% of fibres with length L(n)<1 mm. The refining phase has variable durations, typically requiring long times (about an hour).

Once the above target has been reached, we then move on to the screening phase, where the refined mixture is purified from coarse residues by means of a mechanical filter 4 with fine slots and is then collected in the second container 5. The residues, on the other hand, advantageously return to the first container 2 for further processing.

Preferably, the slits of the mechanical filter 4 have a length of the order of a few centimetres and a width of substantially between 0.1 and 0.2 mm.

The resulting mixture 1, which looks like a light brown mud, can be advantageously combined with typical mixtures from the paper sector made with poor cellulose (recycled paper or short fibres) with easy and good integration with the other fibres.

Due to the high flowability value (?SR >90) it is practically impossible to produce sheets of paper with 100% of this mixture 1.

For this reason, the mixture 1 is added to the other mixtures of cellulose fibres typical of paper production in percentages between 2 and 30% of the dry weight.

From the above description it can be seen how the invention achieves the proposed task and aims and in particular it is highlighted that a mixture is created for the production of paper, particularly recycled paper, based on eco-sustainable annual alternative fibres which, if added to traditional paper mixtures, increase their performance.

In particular, using this mix in paper production will result in high performance increases and, depending on the percentage used, the resistance of the sheet produced can even double or triple.

Another advantage of the invention is given by the fact that the manufacturing process for obtaining the mixture which is the object of the patent is totally compatible with the paper recycling process currently used.

Another advantage of the mixture according to the invention is given by the fact that it was obtained with hemp that is easily cultivated and available, so much so that Italy was among the leading producers of hemp in the world until the early 1900s. Last but not least, the use of means easily available on the market and the employment of common materials make the process for the creation of a mixture for the production of paper, particularly recycled paper, containing hemp fibres economically competitive.

The invention thus conceived is susceptible to numerous modifications and variations, all of which fall within the scope of the inventive concept.

Furthermore, all details may be replaced by other technically equivalent elements.

In practice, the materials used, as well as the dimensions, can be any according to the needs, as long as they are consistent with the construction purpose.

Claims (11)

1) A mixture (1) for the production of paper, particularly recycled paper, comprising hemp fibres, preferably cannabis sativa, containing: a statistical mean length less than or equal to substantially 0.6 mm, preferably less than or equal to substantially 0.5 mm; and a statistical mean width substantially between 10 and 20 ?m, extremes included, preferably substantially between 12 and 18 ?m, extremes included. 2) The mixture (1) according to claim 1, wherein at least 50% of the hemp fibres have a length substantially less than 0.2 mm and/or at least 40% of the hemp fibres have a length substantially between 0.2 and 0.5 mm 3) The dough (1) according to claim 1 or 2, wherein a portion substantially comprised between 92 and 99%, ends included, of the fibres has a length of less than 1 mm, said portion being preferably comprised substantially between 91 and 97%, ends included, more preferably comprised substantially between 91 and 96%, ends included, even more preferably comprised substantially between 91 and 95%, ends included. 4) The dough (1) according to one or more of the preceding claims, comprising a flow index substantially of at least 90 according to the Schopper-Riegler measurement model. 5) The process for the production of a mixture (1) for the production of paper, particularly for the production of recycled paper, containing hemp fibres, preferably cannabis sativa, comprising the phases consisting of: - soak said hemp fibres in a first container (2) containing water, with a concentration substantially between 3 and 5% of the dry weight, at a temperature preferably between 20 and 40 °C for a period substantially between 12 and 24 hours, so as to promote the imbibition of said macerated hemp fibres; - pulp the soaked hemp fibres, gradually inserting them into a refiner (3) and diluting them with water to obtain a mixture with a concentration substantially between 0.5 and 2%, for substantially 20-30 minutes; - circulate the mixture of fibres to be pulped in a closed circuit, inside said refiner (3) without applying pressure, so as to progressively increase the density of said fibres to be pulped, until adequate homogenisation is obtained in the circuit of said refiner (3) itself and until said first container (2) is completely emptied; - refine the fibres thus obtained in a cyclical manner in a closed circuit, progressively applying pressure until reaching a pressure substantially equal to a value of at least 150 KPa; - purify the refined mixture from any coarse residues using a mechanical filter (4) with fine slots and collect said mixture (1) in a second container (5). 6) The process according to the preceding claim, comprising the step of controlling the refining by carrying out free-flow measurements, verifying that said refined mixture has a free-flow index greater than or equal to a predefined value, so that, once this value has been exceeded, a further check is carried out on the statistical mean length and the refining is continued until a mixture is reached with fibres having a statistical mean length less than or equal to substantially at least 0.6 mm, preferably less than or equal to substantially 0.5 mm and a statistical mean width of substantially between 10 and 20 ?m, ends included, preferably substantially between 12 and 18 ?m, ends included. 7) The method according to the preceding claim, wherein said predefined value corresponds substantially to 90 according to the Schopper-Riegler measurement model. 8) The process according to one or more of claims 5-8 wherein the production is foreseen in successive batches of fibres which are worked by passing from said first container (2) to said second container (5). 9) A sheet of paper made from a mixture (1) according to one or more of claims 1-4. 10) A method of producing a sheet of paper, particularly for producing a sheet of recycled paper, comprising the step of adding the mixture (1) of hemp fibres, preferably of cannabis sativa, according to one or more of claims 1-4 to a mixture of celluloses, preferably of poor celluloses. 11) The method according to the preceding claim, wherein the percentage of the mixture (1) of hemp fibres is substantially between 1 and 35%, extremes included, preferably between 1 and 33%, extremes included, more preferably between 2 and 32%, extremes included, even more preferably between 2 and 30%, extremes included.