EP0668396A1 - Process for making cardboard having antislip properties, and cardboard obtained - Google Patents

Abstract

For the prodn. of corrugated cardboard, with at least one non-slip surface, the paper is coated with a material containing water or a solvent with a thermoplastic resin. The resin contains hollow microcapsules with a thermoplastic polymer shell. They contain one or more volatile liquids. The coating is effected at a temp. lower than the liquid phase change or vol. expansion temp. The coated paper (12) is dried at a temp. to evaporate the water or solvent in the coating, but at a lower temp. than that which expands the micro capsules. The dry coated paper is fed to a corrugated cardboard prodn. machine, with the coated surface presented to form an outer surface of the cardboard. The corrugated cardboard is heated to bond the adhesive between the layers (12, 16, 20) and expand the micro capsules in the coating, while softening the resin and polymer shells to take up their expansion.

Description

The invention relates to a new process for producing cardboard, and in particular corrugated cardboard, at least one of the faces of which has anti-slip properties. The invention also relates to the cardboard, in continuous form or in the form of plates, provided with such properties, obtained by this process.

The term “anti-slip” properties is understood to mean the properties developed by certain supports, such as in particular papers, films, nonwovens, etc., which, although devoid of glue or any other similar adhesive system, exhibit a certain resistance. when positioned on their dish on any coating, they are subject to displacement on and parallel to this coating. In fact, these properties are generally sought after when the supports are positioned on smooth coatings or, in the field of packaging, transport and packaging.

In the context of the transport and storage of goods, the pallet dividers made of corrugated cardboard, agglomerated wood or another type of cellulosic material, have the disadvantage of having slippery faces, and in any case devoid of properties d adhesion or anti-slip likely to oppose the movement of the products they receive, and therefore risk causing damage to these products thus packaged during handling and transport.

In order to overcome this prohibitive drawback, it has been proposed to use spacers made of corrugated cardboard, at least one of the faces of which is treated with adhesive products, colloidal silicas, paraffins, colloidal alumina suspensions. These compounds of processing are generally deposited on the corrugated cardboard at the end of the corrugating line using traditional equipment of the sponge type, with equipment with a coating roller, or using a flexographic group.

Although constituting a progress, these spacers still do not give satisfaction, taking into account on the one hand, their still insufficient anti-slip properties, on the other hand their mediocre qualities of printability, but also because of their unpleasant touch , their awkward handling, or all of these various drawbacks.

If to date, the manufacture of anti-slip paper is relatively simple to implement, it is not the same for corrugated cardboard. Indeed, by the very fact of the processes for manufacturing such corrugated cardboard, and by the rigidity which characterizes the cardboard, the methods for producing anti-slip paper are not applicable to it.

Indeed, such a method consists in coating at least one of the faces of a sheet of paper in movement with a coating layer consisting of a thermoplastic resin containing hollow microspheres, the envelope of which is produced in a polymer also thermo-plastic, and the core of which contains a volatile fluid, the coating being carried out at a temperature below the temperature of phase change or volume expansion of said fluid. The sheet thus formed is then subjected to a specific heat treatment on the one hand, to induce the softening of the thermoplastic resin containing the microspheres, but also the softening of the polymer constituting the envelope of said microspheres, and on the other hand , to induce either the expansion of the gas, or the change of phase of the fluid, resulting in one case as in the other by the expansion volume of said microspheres. The sheet thus treated is then subjected to a cooling phase, freezing the microspheres thus expanded in their final size, effectively conferring its anti-slip properties, inherent in the projections formed by said microspheres relative to the general plane of the sheet.

However, applying this treatment during the manufacture of corrugated cardboard is technically impossible. Indeed, the production of corrugated cardboard is conventionally carried out by means of a corrugator. In fact, if sheets of paper endowed with non-slip properties are used directly according to this process prior to the production of the cardboard, the installation is inevitably blocked, taking into account the significant friction forces generated by said paper at the level of the different components of the installation, forces inherent in the anti-slip properties of said paper, and therefore leading to a technical impossibility of production.

The invention aims to provide a method of producing corrugated cardboard endowed with anti-slip properties overcoming these various drawbacks, and capable of also developing good printability properties and a pleasant touch.

• tout d'abord, à enduire une feuille de papier d'une composition d'enduction comprenant un solvant ou de l'eau, une résine thermo-plastique faisant office de liant, contenant des microsphères creuses dont l'enveloppe est réalisée en un polymère également thermo-plastique, et dont le coeur renferme un ou plusieurs fluides volatils, l'enduction s'effectuant à une température inférieure à la température de changement de phase ou d'expansion volumique dudit fluide ;
• à sécher le papier ainsi enduit à une température suffisante pour permettre l'évaporation de l'eau ou du solvant de ladite composition d'enduction, mais inférieure à la température susceptible de générer l'expansion des microsphères ;
• puis à utiliser le papier ainsi enduit et séché au niveau d'une installation de fabrication de carton ondulé (onduleuse), de telle sorte à servir de support inférieur et/ou supérieur dudit carton, la face enduite du papier étant dirigée vers l'extérieur du carton ainsi réalisé.
• et enfin à soumettre le carton ondulé ainsi réalisé à une phase de chauffage destinée, d'une part à assurer le séchage de la colle de solidarisation des feuilles constitutives du cartton, et d'autre part à permettre l'expansion volumique des microsphères de la couche d'enduction de ladite feuille de papier enduite, rendue possible par le ramollisement d'une part, de la résine thermo-plastique constitutive de la couche d'enduction et de l'enveloppe proprement dite des polymères constitutifs des microsphères.

This process for producing corrugated cardboard, at least one of the faces of which has anti-slip properties is characterized in that it consists:

• first, to coat a sheet of paper with a coating composition comprising a solvent or water, a thermoplastic resin acting as a binder, containing hollow microspheres whose envelope is made of a polymer also thermo-plastic, and the core of which contains one or more volatile fluids, the coating taking place at a temperature below the phase change or volume expansion temperature of said fluid;
• drying the paper thus coated at a temperature sufficient to allow the evaporation of water or of the solvent of said coating composition, but below the temperature capable of generating the expansion of the microspheres;
• then to use the paper thus coated and dried at a corrugated cardboard manufacturing plant (corrugator), so as to serve as a lower and / or upper support for said cardboard, the coated side of the paper being directed towards the outside cardboard thus produced.
• and finally to subject the corrugated cardboard thus produced to a heating phase intended, on the one hand to ensure the drying of the adhesive for securing the constituent sheets of the carton, and on the other hand to allow the volume expansion of the microspheres of the coating layer of said coated sheet of paper, made possible by softening on the one hand, of the thermoplastic resin constituting the coating layer and of the envelope proper of the polymers constituting the microspheres.

According to a variant of the invention, the two faces of the cardboard are endowed with anti-slip properties, the second sheet of cardboard being in this case also previously coated according to the method described above.

Finally, the invention relates to sheets of cardboard paper obtained by this process, one or both sides of which have expanded microspheres of diameter varying between 10 and 100 μm, projecting from the coating layer coating the said at least one faces.

The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the example of embodiment which follows, given by way of indication and without limitation in support of the appended figures.

Figure 1 is a schematic representation of a known installation for coating a sheet of paper.

Figure 2 is a schematic representation of an installation for the manufacture of corrugated cardboard.

FIG. 3 is a representation of a cardboard sheet having anti-slip properties on its two faces, obtained according to the method of the invention.

With reference to FIG. 1, an installation is described intended for the production of a sheet of paper constituting the cardboard, intended to subsequently exhibit anti-slip properties.

This installation is more widely described in document FR-A-2 673 209, of the Applicant, so that it will only be described here briefly.

It basically comprises a reel (1) on which is mounted a reel of paper, such as in particular Kraft-unbleached paper, for example of grammage 150 g / m². This moving paper is kept under slight mechanical tension by means of conventional systems, and is brought by means of positive delivery rollers (10) to a coating zone (6), respectively comprising deflection rollers (7 , 8), and a coating roller (5), plunging into a coating tank (4) containing the coating composition (3), as described in Table I below.

The excess coating composition on the paper (2) is removed by means of a scraper or an air knife (9), the pressure of which can be adjusted in order to obtain a coating layer d '' greater or lesser and uniform thickness, the excess of composition falling back into the coating tank (4).

The coating temperature is lower than the expansion temperature of the volatile gas contained in the microspheres.

The coated paper (12) is then dried, to allow the evaporation of the water or of the solvent contained in the coating composition.

A paper coated with a thermoplastic resin and microspheres containing a volatile gas or liquid having a diameter between 5 and 20 μm is thus obtained. This paper behaves like ordinary paper and has no anti-slip properties.

The paper (12) thus coated is stored again in the form of a reel (11), capable of being transferred to the level of the installation for the production of corrugated cardboard, as shown in FIG. 2.

The coated paper (12) is therefore unwound from the spool (11), placed on a reel, and tensioned by traditional return rollers (13), then is conveyed to multiple rollers (17) at which the face uncoated receives on the one hand, the intermediate groove paper (16), and on the other hand, the other sheet of support paper (20) constituting said cardboard.

The intermediate groove paper comes from a reel (14) of paper, undergoing in the form of grooves (15), said groove paper (16) then being conveyed to the device (17).

As a corollary, the other sheet of paper (20) constituting the cardboard is conveyed via return rollers (19) from a storage reel (18) to the device (17).

The assembly thus constituted, namely coated sheet of paper (12), intermediate corrugated paper (16) and other support sheet (20), not yet joined together, is conveyed at the level of a glue bath (28), intended to allow the gluing of the intermediate groove paper (16) at the two internal faces of the external support sheets, respectively (12) and (20).

The assembly (21) thus glued is routed to a heated enclosure (22), intended to ensure the drying of the adhesive, the heating being regulated by a traditional device (23), consisting of electrical resistors or d 'an infrared source.

This drying phase also makes it possible to evaporate the residual water contained in the coating composition for coated paper (12), and is adjusted so that the coated sheet of paper (12) reaches a temperature of the paper above 90 ° C.

In this way, under the effect of the temperature, the constituent copolymer of the microspheres softens. In addition, the gas contained in said microspheres expands, inducing, given the softening of the envelope of the microspheres, the swelling of the latter so that they reach a diameter of approximately 40 to 60 μm, or even 100 μm. . In addition, the temperature also induces softening of the coating resin, so that although having expanded, said microspheres remain attached to the support.

At the outlet of the enclosure (22), positive rollers (24) ensure the progression of the corrugated cardboard thus produced, conveying it at a cutting device (25), in order to allow the cardboard to be cut according to a format programmable, and the storage of the cardboard sheets in the form of a stack (26), adjustable in height by an appropriate device (27).

In an advantageous embodiment of the invention, and when required, the two sheets of backing paper enclosing the sheet of cardboard intermediate groove of the cardboard can be coated beforehand, before the constitution of the cardboard itself, so as to obtain a cardboard whose two faces develop anti-slip properties, and for example shown in FIG. 3.

In this one, one can thus observe on the external faces of the sheets respectively (12) and (20) of the cardboard enclosing the intermediate corrugated paper (16), the layers of resin (29) and (30) integrating the microspheres (31 ) which, under the effect of the expansion, protrude from the general plane of the resin layer, thus giving the two sides of the cardboard its anti-slip properties.

The cardboard sheets thus produced are particularly suitable for use as dividers, in particular for packaging, and the packaging of large loads, thus making it possible to store, at relatively large heights, products of various natures, without risk of destruction of the batteries, especially during transport and other handling.

In addition, the process used to produce such sheets of corrugated cardboard can be carried out with conventional cardboard manufacturing installations, by appropriately regulating the heating conditions allowing the microspheres to expand sufficiently, but not excessive. For example, a temperature of 150 ° C. made it possible to manufacture corrugated cardboard with good quality anti-slip properties and good flatness at the speed of 120 m / min.

In order to better understand the invention, exemplary embodiments are described below.

Aqueous coating compositions are prepared with different compounds indicated in Table I below. The amounts are expressed as a percentage by weight. The microspheres are formed by hollow capsules produced for example from polyvinylidene chloride, or from polyvinylidene chloride - acrylonitrile copolymer. They contain pentane, neopentane or isobutane. Their diameter is between 5 and 20 µm. The coating composition further comprises a thermoplastic binder resin, for example a styrene-butadiene latex, an ethylene vinyl vinyl copolymer, an acrylic resin, or any other thermoplastic resin preferably having a glass transition point of less than 25 °. vs.

Depending on the technology used, the deposited coating composition may also contain other substances well known in the field of paper coating, such as dyes, pigments, plasticizers, antistatic agents, surfactants. , etc.

The weight deposited in dry quantity is approximately 3 to 5 g / m²; the aqueous composition being deposited according to known techniques for coating paper (air knife coating, Meyer bar, engraved cylinder, etc.)

EXAMPLE 1

A 300 g / m² Kraftliner paper is coated with an aqueous coating composition as described in table I, preferably one of the compositions referenced 2 to 6. The paper is then dried in an oven so as to evaporate the water without the paper itself reaching a temperature of 90 ° C. Since the microspheres are not expanded, the paper thus treated does not have anti-slip properties, and can therefore without difficulty be used on a corrugator for the production of corrugated cardboard.

Two Kraftliner papers of 300 g / m² thus coated are used as support sheets on a corrugator, respectively in position (11) and (18) (figure 2), on either side of a third interkraft reel of 120 g / m², constituting the core of the groove. After the glue, starch-based, used at 150 ° C has dried, the microspheres of the supports expand, thus giving the external faces of the corrugated board anti-slip properties, at the exit of the corrugator, just before the automatic formatting installation ((25, 26, 27).

EXAMPLE 2

A 150 g / m² Kraftliner coated according to the process described in Example 1, and used in position (11) (Figure 2) of the corrugator, as well as an untreated 150 g / m² kraftliner used in position ( 18) allow, under the same conditions, to obtain corrugated cardboard having anti-slip properties on only one of its faces.

EXAMPLE 3

A 150 g / m² paper, consisting of two jets of pulp, namely 100 g / m² of bleached pulp and 50 g / m² of unbleached pulp, is coated on the white side using a coating composition aqueous of Table I, then is treated according to Example 1 and positioned at (11) on the corrugator of FIG. 2. A kraftliner of 150 g / m² is treated identically and used in position (18) on the corrugator of Figure 2. According to the method described in Example 1, one thus obtains a corrugated cardboard whose two sides develop anti-slip properties, and which has a better aesthetic appearance, and capable of being printed in flexography directly on the corrugator.

EXAMPLE 4

A 150 g / m² paper made up of two jets of pulp, namely 100 g / m² of bleached pulp and 50 g / m² of unbleached pulp, is printed by flexographic process, then is coated on the white side using 'an aqueous coating composition from Table I, then is then treated according to Example 1, and finally positioned in (11) on the corrugator of Figure 2.

A 150 g / m² kraftliner is treated according to Example 1, then used in position (18) on the corrugator of FIG. 2.

According to the process of the invention, a printed corrugated cardboard is then obtained, developing anti-slip properties on its two faces.

In order to obtain a better printing quality in flexography at the end of the corrugator, it may be advantageous to introduce pigment fillers into the coating composition, according to the examples given in a nonlimiting manner in Table II. TABLE II Microspheres Binder Koalin CaCO₃ CHC 20 25 0 54 1 15 25 10 44 1 10 25 20 34 1

EXAMPLE 5

A 150 g / m² paper made up of two pulp jets, namely 100 g / m² of bleached pulp and 50 g / m² of unbleached pulp, is coated on the white face using an aqueous coating composition of Table II and is positioned in (11) on the corrugator of FIG. 2. A 150 g / m² kraftliner is treated identically and used in position (18) on the corrugator of FIG. 2.

According to the method described in Example 1, one then obtains a corrugated cardboard having two non-slip faces, and also allowing very high quality flexographic printing.

Claims (4)

1 / Method for producing corrugated cardboard, at least one of the faces of which has anti-slip properties, characterized in that it consists of: - firstly, to coat a sheet of paper (2) with a coating composition (3) comprising a solvent or water, a thermoplastic resin acting as a binder, containing hollow microspheres, of which the envelope is made of a polymer also thermo-plastic, and the core of which contains one or more volatile fluids, the coating being carried out at a temperature below the temperature of phase change or volume expansion of said fluid; - Then drying the paper (12) thus coated at a temperature sufficient to allow the evaporation of the water or the solvent of said coating composition (3), but below the temperature capable of generating the expansion of the microspheres ; - then to use the paper thus coated and dried at a corrugated cardboard manufacturing installation, so as to serve as a lower and / or upper support for said cardboard, the coated side of the paper being directed towards the outside of the cardboard corrugated thus produced; - And finally to subject the corrugated cardboard thus produced to a heating phase intended, on the one hand to ensure the drying of the adhesive for securing the sheets (12, 16, 20) constituting the carton, and on the other hand to allow the volume expansion of the microspheres of the coating layer of said coated sheet of paper, made possible by the softening on the one hand, of the thermoplastic resin constituting the coating layer and of the envelope itself constituent polymers of microspheres. 2 / A method for producing sheets of cardboard, at least one of the faces of which has anti-slip properties according to claim 1, characterized in that the two sheets (12, 20) of the cardboard enclosing the sheet of fluted paper intermediate (16) are previously coated on one of their faces with the coating composition containing the microspheres, capable of expanding during the drying phase. 3 / A method for producing cardboard sheets, at least one of the faces of which has anti-slip properties according to one of claims 1 and 2, characterized in that the cardboard sheet (21) after the area of drying is cut (25) according to a configurable format, then stored on a stack (26) adjustable in height. 4 / corrugated cardboard sheet developing on at least one of its faces anti-slip properties, obtained according to the method of one of claims 1 to 3, and having on the said face (s) a plurality of expanded microspheres of diameter varying between 10 and 100 micrometers, projecting from the coating layer coating the said face or faces.

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