Method for Manufacturing Reduced-Weight Paper, Thin Cardboard and Cardboard, and Compounds Obtained Therewith

Description

The present invention concerns a method for preparing compounds for the manufacture of paper or cardboard or thin cardboard both in paper machines on an industrial scale and manually, according to traditional handicraft techniques.

The present invention also concerns the compounds obtained with the above mentioned method.

As is known, the paper usually manufactured both in paper machines and with handicraft techniques consists of fibrous, generally vegetable raw materials, felted together and then dried.

The material that is most commonly used for manufacturing paper is constituted by cellulose fibres obtained from trees or plants in general.

The surface of the raw paper is then covered using a range of additives that form a coat.

The coating agents are generally starch, polyvinyl acetate (PVA) and many other products suitable for making different types of paper.

The paper obtained in this way, however, has some drawbacks.

A drawback is due to the fact that normally the paper produced, when it is bulky, is also rather heavy and difficult to transport.

This is the cause of the excessive weight of books, for example school books, which may damage in particular the backbone when the books are transported in school bags that students carry on their backs.

Similarly, also the documents kept in bags or folders are rather heavy when they are bulky.

A further drawback is due to the fact that paper manufacturing costs are a consequence of the high quantity of cellulose fibres used and of felled trees.

The object of the present invention is to carry out a compound for manufacturing paper and/or cardboard and/or thin cardboard that, considering the same volume produced, greatly reduces its weight and consequently makes it easier to transport for the user.

A further object of the present invention is to carry out a compound that solves the problem of the damage to the backbone due to the excessive weight carried.

It is another, yet not the least object of the invention to carry out a compound that, considering the same volume of paper and/or cardboard and/or thin cardboard to be manufactured, allows a reduced quantity of cellulose fibres to be used for making paper.

The objects mentioned above are achieved by the present invention concerning a compound for the manufacture of paper or cardboard, whose main principles are in accordance with the contents of the first claim, as well as a method for the production of the above mentioned compound.

Advantageously, the compound carried out according to the invention allows the apparent specific weight of copy or printing paper to be reduced from 1.0 to at least 0.5.

Still advantageously, the compound carried out according to the invention allows the paper to be recycled with no need for any separation of the material from which it is made.

Still to advantage, the compound carried out according to the invention allows paper and cardboard to be manufactured that are more elastic and flexible than the paper and cardboard of known type.

According to the present invention, the production of paper and cardboard is achieved by using virgin cellulose fibres and/or fibres recycled before or after use, even if with the addition of suitable auxiliary substances like bonding agents, mineral fillers, starches and coating agents, in combination with a water dispersion of substances that expand when heated and generate closed microbubbles.

The microbubbles that expand when heated, in order to function as expanding agents for the paper panel in the most suitable way, are added to the fibre suspension (that is, the paper pulp) before the addition of the suitable cohesion agents.

Cationic starch in solution has resulted to be particularly suitable and effective.

The cationic starch in solution has been normally employed here before the formation of the fibre panel that takes place on the paper wire.

The dispersion particles that expand when heated, firmly anchored to the constituent parts of the paper panel, were left to rise at the same time as the paper and/or cardboard sheet was dried.

In order to ensure the best possible development of the expanding function in paper, the temperature of the drying cylinders (or of the drying plate, if the paper is handmade) must exceed 110° C. and at such temperatures the contact time of the paper panel, in which also the cellulose bonds form, must be sufficient to ensure the drying of the sheet with at least 88% of dry material.

Some non-limiting examples of formulation of the compound carried out according to the invention are illustrated here below.

EXAMPLE N. 1

Here paper is manufactured using 4% of polymer in the form of expandable thermoplastic microspheres encapsulating a gas, produced by Akzo Nobel and marketed under the Expancel® trademark.

In this case, 20 kg of a dispersion of Expancel® were added to a water dispersion having a dry concentration usually included between 0.4% and 7%, constituted by 100 kg of whitened cellulose obtained from fir, by 280 kg of whitened cellulose obtained from eucalyptus and by 50 kg of micronized calcium carbonate.

35 kg of a water dispersion of diketenic synthetic bonding agent were added to this pulp.

This type of bonding agent makes paper suitable for writing with water inks.

This pulp is always kept under slight agitation and then mixed with 7.5 kg of cationic starch dry solution, with the purpose of obtaining good retention and increasing the number of bonding contacts between fibres, auxiliary substances and expandable bubbles.

In order to increase the surface strength characteristics of the paper panel, paper was impregnated in the size press of the paper machine with a 3% dry solution of maize starch.

The manufacturing speed of the paper strip was 50 m/min.

The drying cylinders coinciding with the points of formation of the cellulose bonds were adjusted at a temperature ranging between 115° C. and 125° C.

It is estimated that a book printed with this paper, with the same format, number of pages and thickness, will weigh 19% less than books manufactured according to the state of the art.

The composition of the pulp is illustrated in Table 1, while the characteristics of the paper produced are illustrated in Table 2.

EXAMPLE N. 2

Here paper is manufactured using 10% of Expancel®.

In this case, 50 kg of a dispersion of Expancel® were added to a water dispersion constituted by 90 kg of whitened cellulose obtained from fir, by 270 kg of whitened cellulose obtained from eucalyptus and by 40 kg of micronized calcium carbonate.

After homogenizing, obtained by slight agitation of the paper pulp, 35 kg of a water dispersion of diketenic synthetic bonding agent were added, which makes paper suitable for writing with water inks.

This pulp is always kept under slight agitation and then mixed with 7.5 kg of cationic starch dry solution, with the purpose of obtaining good retention and increasing the number of bonding contacts between fibres, auxiliary substances and expandable bubbles.

In the paper panel drying and rising stage, the drying cylinders coinciding with the points of formation of the cellulose bonds were adjusted at a temperature ranging between 115° C. and 125° C.

In order to increase the surface strength characteristics of the paper panel, paper was impregnated in the size press of the paper machine with a 3.5% dry solution of maize starch.

The manufacturing speed of the paper strip was 50 m/min.

It is estimated that a book printed with this paper, with the same format, number of pages and thickness, will weigh 35% less than books manufactured according to the state of the art.

The composition of the pulp is illustrated in Table 1, while the characteristics of the paper produced are illustrated in Table 2.

EXAMPLE N. 3

Here paper is manufactured using 20% of Expancel®.

100 kg of Expancel® dispersion consisting of particles having a diameter of a few microns were used.

In this case, the dispersion of Expancel® was added to a water dispersion constituted by 90 kg of whitened cellulose obtained from fir, by 240 kg of whitened cellulose obtained from eucalyptus and by 30 kg of micronized calcium carbonate.

30 kg of a water dispersion of diketenic synthetic bonding agent, which makes paper suitable for writing with water inks, were added to the pulp.

This pulp was always kept under slight agitation and then mixed with 7.5 kg of cationic starch dry solution, with the purpose of obtaining good retention and increasing the number of bonding contacts between fibres, auxiliary substances and expandable bubbles, in particular during the paper panel drying and rising stage.

The manufacturing speed of the paper strip was 50 m/min.

The drying cylinders coinciding with the points of formation of the cellulose bonds were adjusted at a temperature ranging between 115° C. and 125° C.

In order to increase the surface strength characteristics of the paper panel, the paper was impregnated in the size press of the paper machine with a 4% dry solution of maize starch.

It is estimated that a book printed with this paper, with the same format, number of pages and thickness, will weigh 49% less than books manufactured according to the state of the art.

The composition of the pulp is illustrated in Table 1, while the characteristics of the paper produced are illustrated in Table 2.

TABLE 1
Composition of industrial paper pulps.

Weight	Industrial
percentage kg/%	reference	Example 1	Example 2	Example 3
Whitened fir	100 kg	100 kg	90 kg	90 kg
cellulose
%	20.3	20.3	18.3	18.1
Whitened eucalyptus	300 kg	280 kg	270 kg	240 kg
cellulose
%	60.9	56.9	54.8	48.2
Calcium	50 kg	50 kg	40 kg	30 kg
carbonate
%	10.1	10.1	8.1	6.0
Expancel	0	20 kg	50 kg	100 kg
%	0	4.1	10.1	20.1
Bonding agent	35 kg	35 kg	35 kg	30 kg
%	7.1	7.1	7.1	6.0
Cationic starch	7.5	7.5	7.5	7.5
%	1.5	1.5	1.5	1.5
Total parts kg	492.5 kg	492.5 Kg	492.5 kg	497.5 kg
%	100.0	100.0	100.0	100.0
Concentration of the	2.5%	3.0%	3.5%	4.0%
solution of anionic
starch in the size press

TABLE 2
Characteristics of industrial papers

	Industrial
Characteristics	reference	Example 1	Example 2	Example 3

Thickness-micron %	165	176	185	193
Grams per	150	130	110	90
square metre
Apparent	0.910	0.737	0.595	0.466
specific weight
Gluing with	excellent	excellent	excellent	excellent
Pelikan 4001
Offset	excellent	excellent	good	moderate
printability
Copybility	good	good	good	good
Backprint	good	excellent	good	good
opacity
Mechanical	excellent	excellent	good	sufficient
workability

EXAMPLE N. 4

In this case the pulp described in Example 1, with the addition of all its constituent parts, was partially used to produce handmade paper sheets.

The fibre suspension was brought to the usual use concentrations, always kept under slight agitation, filtered on the wire of the handmade paper panel according to the traditional manufacturing techniques, pressed and detached from the forming wire, and then transferred onto normal dry felts, and wet-pressed following the usual techniques.

The fibre panel has then assumed such a consistency as to be able to be easily separated from the absorbing agents.

According to the traditional paper manufacturing techniques, the paper or cardboard panel is laid and let to dry in the air at ambient temperature.

In this and in the following examples, in order to allow the thermal expansion of the gases encapsulated in the Expancel® microspheres and to obtain both the rising of the fibre panel and a sufficient cohesion of the constituent parts of the paper panel and of the relevant bonds, the handmade paper sheets, still quite humid (40-70% of water) were transferred onto a drying plate with temperature adjusted at 120° C. and provided with a counter-felt exerting a slight pressure.

In these conditions, handmade cellulose sheets were obtained in a few seconds.

The characteristics of the paper produced are illustrated in Table 3.

EXAMPLE N. 5

Also in this case, like in Example 4, the handmade paper sheets, still very humid (40-70% of water), were transferred onto a drying plate with temperature adjusted at 120° C. and provided with a counter-felt exerting a slight pressure.

Expanded handmade sheets were produced in this case with the pulp sample of Example 2.

The characteristics of the paper produced are illustrated in Table 3.

EXAMPLE N. 6

Also in this case, like in Examples 4 and 5, the handmade paper sheets, still very humid (40-70% of water) were transferred onto a drying plate with temperature adjusted at 120° C. and provided with a counter-felt exerting a slight pressure.

Expanded handmade sheets were produced in this case with the pulp sample of Example 3.

The characteristics of the paper produced are illustrated in Table 3.

TABLE 3
Composition of handmade paper pulps.

Weight	Hand
percentage	making
kg/%	reference	Example 4	Example 5	Example 6
Whitened fir	100 kg	100 kg	90 kg	90 kg
cellulose	20.3%	20.3%	18.3%	18.1%
Whitened	300 kg	280 kg	270 kg	240 kg
eucalyptus
cellulose	60.9%	56.9%	54.8%	48.2%
Calcium	50 kg	50 kg	40 kg	30 kg
carbonate	10.1%	10.1%	8.1%	6.0%
Expancel	0	20 kg	50 kg	100 kg
	0	4.1%	10.1%	20.1%
Bonding agent	35 kg	35 kg	35 kg	30 kg
	7.1%	7.1%	7.1%	6.0%
Cationic	7.5 Kg	7.5 Kg	7.5 Kg	7.5 Kg
starch	1.5%	1.5%	1.5%	1.5%
Total parts	492.5 kg	492.5 kg	492.5 kg	497.5 kg
	100.0%	100.0%	100.0%	100.0%

TABLE 4
Characteristics of handmade papers

	Hand making
Characteristics	reference	Example 4	Example 5	Example 6

Thickness-micron %	215	241	292	375
Grams per	150	144	138	122
square metre
Apparent	0.70	0.60	0.47	0.32
specific weight
Gluing with	good	good	good	good
Pelikan 4001
Physical-	moderate	moderate	moderate	moderate
mechanical
consistency

The paper obtained according to the examples described has a natural, valuable aspect and is also pleasant to touch.

As an alternative to Expancel®, it will be possible to use other products to generate microbubbles, like Avancell® (copolymers of acrylonitrile) and Micropearl® (copolymers of divinylbenzene).

As colloidal agents it is possible to use cationic agents, anionic agents, non-ionic agents alone or mixed with each other and/or in a different time frequency with colloids and/or retaining and/or fixing agents that at the same time considerably increase the physical-mechanical characteristics of the finished paper panel of papers and cardboards.

An example of a non-ionic agent is polyoxypropylene that, thanks to its high specific weight, allows a considerable quantity of product to be saved when combined with a cationic or anionic agent.