EP0668396B1 - Process for making cardboard having antislip properties - Google Patents

Description

The invention relates to a new method for carrying out cardboard, and in particular corrugated cardboard, at least one of the faces 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.

By "anti-slip" properties, we mean the properties developed by certain supports, such as in particular papers, films, nonwovens, etc., which although free of glue or any other adhesive system analogous, have some resistance when positioned on their dish on any coating, they are subjected to a 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.

As part of the transportation and storage of goods, pallet dividers made of corrugated cardboard, chipboard or in another type of cellulosic material, have the disadvantage of present slippery faces, and in any case devoid of properties grip or anti-slip likely to oppose the movement of products they receive, and therefore risk causing damage to these products thus packaged during handling and transport.

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

Although they constitute progress, these dividers do not give still not satisfied, taking into account on the one hand, their anti-slip properties still insufficient, on the other hand of their mediocre qualities printability, but also because of their unpleasant touch, their awkward handling, or all of these different disadvantages.

If to date, the manufacture of anti-slip paper is relatively simple to implement, it is not the same when it comes to cardboard corrugated. Indeed, by the very fact of the manufacturing processes of such cartons corrugated, and by the rigidity that characterizes cardboard, the methods of making non-slip paper do not apply to it.

Indeed, such a method consists in coating at least one of the faces of a sheet of paper running through a coating layer made of a thermoplastic resin containing microspheres hollow, whose envelope is made of a polymer also thermo-plastic, and whose core contains a volatile fluid, the coating taking place at a temperature below the temperature of change of phase or volume expansion of said fluid. Leaf thus formed is then subjected to its own heat treatment on the one hand, to induce the softening of the thermoplastic resin containing the microspheres, but also the softening of the constituent polymer of the envelope of said microspheres, and other part, to induce either the gas expansion, or the phase change of the fluid, resulting in either case in the expansion volume of said microspheres. The leaf thus treated is then subjected to a cooling phase, freezing the microspheres as well expanded to their final size, effectively imparting its anti-slip properties, inherent in the projections formed by said microspheres by relation to the general plan of the sheet.

However, apply this treatment during the manufacture of corrugated cardboard is technically impossible. Indeed, the realization of the cardboard corrugated is conventionally carried out using a corrugator. In fact, if sheets of paper with anti-slip properties are used directly according to this process prior to the production of the cardboard, we end up inevitably when the installation is blocked, given the important frictional forces generated by said paper at the level of the different system components, forces inherent in said anti-slip properties paper, and therefore leading to a technical impossibility of production.

The invention aims to propose a method for producing cardboard corrugated with anti-slip properties overcoming these different disadvantages, and likely to also develop 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 the 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 (corrugating) manufacturing facility, so as to serve as a lower and / or upper support for said cardboard, the coated side of the paper being directed outward 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 carton are endowed with anti-slip properties, the second sheet of cardboard being in this case also previously coated according to the process described previously.

The manner in which the invention can be realized and the advantages which will emerge more clearly from the example of embodiment which follows given as an indication and not limiting in support of the appended figures.

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

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

Figure 3 is a representation of a sheet of cardboard having anti-slip properties on both sides, obtained using the the invention.

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

This installation is more widely described in document FR-A-2 673 209, of the Applicant, and FR-A-2 395 141 so that it will only be described here succinctly.

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 / m ² . This scrolling 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 with by means of a squeegee or an air knife (9), the pressure of which can be adjusted in order to obtain a more or less thick coating layer large and uniform, the excess composition falling back into the tank coating (4).

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

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

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

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

The coated paper (12) is therefore unwound from the reel (11), placed on a reel, and tensioned by traditional return rollers (13), then is routed to multiple rollers (17) at which the uncoated side receives on the one hand, the intermediate fluting 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 (15) the shaping of grooves, said paper groove (16) then being routed to the device (17).

As a corollary, the other sheet of paper (20) constituting the cardboard is routed via idler 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 still joined together, is routed at 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 an enclosure heated (22), intended to ensure the drying of the adhesive, the adjustment of the heating being provided by a traditional device (23), consisting of electrical resistances or an infrared source.

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

In this way, under the effect of temperature, the constituent copolymer microspheres softens. In addition, the gas contained in said microspheres expands, inducing given the softening of the envelope of the microspheres the swelling of these so that these reach a diameter of around 40 to 60 µm, or even 100 µm. Of plus, the temperature also induces softening of the resin coating, so that despite 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, transporting it to a level cutting device (25), in order to allow the cardboard to be cut according to a programmable format, and storage of cardboard sheets as a stack (26), adjustable in height by a suitable device (27).

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

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

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

In addition, the method used to produce such sheets of corrugated cardboard is achievable with installations of production of traditional cardboard, adjusting the heating conditions allowing the expansion of microspheres sufficiently, but not excessively. A temperature of 150 ° C allowed for example, to make a cardboard corrugated with good anti-slip properties, and good flatness at a 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 quantities are expressed as a percentage by weight. The microspheres are made up by hollow capsules made, for example, of polyvinylidene, or as a polyvinylidene chloride copolymer - acrylonitrile. They contain pentane, neopentane or isobutane. Their diameter is between 5 and 20 µm. The composition coating also comprises a thermo-plastic binder resin, by example a styrene-butadiene latex, an ethylene acrylic copolymer vinyl, acrylic resin, or any other thermoplastic resin preferably having a glass transition point of less than 25 ° C.

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 / m ² ; 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 / m ² Kraftliner paper is coated using an aqueous coating composition as described in Table I, preferably one of the composition referenced 2 to 6. The paper is then dried in a 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 / m ² thus coated are used as support sheets on a corrugator, respectively in position (11) and (18) (figure 2), on either side of a third reel of interkraft of 120 g / m ² , 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 end of the corrugator, just before the automatic formatting installation ((25, 26, 27).

EXAMPLE 2

A 150 g / m ² 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 / m ² kraftliner used in position (18) allow under the same conditions to obtain a corrugated cardboard having anti-slip properties on only one of its faces.

EXAMPLE 3

A 150 g / m ² paper, consisting of two jets of pulp, namely 100 g / m ² of bleached pulp and 50 g / m ² of unbleached pulp, is coated on the white face using a composition of aqueous coating of Table I, then is treated according to Example 1 and positioned in (11) on the corrugator of FIG. 2. A kraftliner of 150 g / m ² is treated in an identical manner and used in position (18 ) on the corrugator of FIG. 2. According to the method described in Example 1, one thus obtains a corrugated cardboard whose two faces 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 / m ² paper made up of two jets of pulp, namely 100 g / m ² of bleached pulp and 50 g / m ² of unbleached pulp, is printed by flexographic process, then is coated on the white side with l using an aqueous coating composition from Table I, then is treated according to Example 1, and finally positioned at (11) on the corrugator of Figure 2.

A 150 g / m ² 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, one then obtains a corrugated cardboard printed, developing anti-slip properties on both sides.

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. Microspheres Binder Koalin CaCO ₃ CHC 20 25 0 54 1 15 25 10 44 1 10 25 20 34 1

EXAMPLE 5

A 150 g / m ² paper consisting of two jets of pulp, namely 100 g / m ² of bleached pulp and 50 g / m ² of unbleached pulp, is coated on the white face with a composition of coating in Table II and is positioned at (11) on the corrugator in Figure 2. A 150 g / m ² kraftliner is treated identically and used in position (18) on the corrugator in Figure 2 .

According to the process described in Example 1, a cardboard is then obtained corrugated with two non-slip faces, and also allowing a very high quality flexographic printing.

Claims (3)

1. Process for the production of corrugated board, at least one of the faces of which possesses non-slip properties, characterized in that it consists:

   firstly, in coating a sheet of paper (2) with a coating composition (3) comprising a solvent or water, a thermoplastic resin acting as binder, containing hollow microspheres, the shell of which is made of a likewise thermoplastic polymer and the core of which contains one or more volatile fluids, the coating being carried out at a temperature below the temperature at which the said fluid undergoes a phase change or an increase in volume;

   then in drying the paper (12) thus coated at a temperature sufficient to allow the water or the solvent of the said coating composition (3) to evaporate, but below the temperature liable to cause the microspheres to expand;

   then in using the paper thus coated and dried in a corrugated board manufacturing plant in such a way as to serve as the bottom and/or top supporting sheet of the said board, the coated face of the paper facing the outside of the corrugated board thus produced;

   and, finally, in subjecting the corrugated board thus produced to a heating step intended, on the one hand, to dry the glue for consolidating the sheets (12, 16, 20) of which the board is composed and, on the other hand, to allow the microspheres of the coating layer on the said coated sheet of paper to expand in volume in order to develop non-slip properties, this expansion being possible because of the softening, on the one hand, of the thermoplastic resin of which the coating layer is composed and of the actual shell of the polymers of which the microspheres are composed [sic].
2. Process for the production of sheets of board, at least one of the faces of which possesses non-slip properties, according to Claim 1, characterized in that the two sheets (12, 20) of the board which flank the intermediate sheet of corrugating medium (16) are precoated on one of their face [sic] with the coating composition containing the microspheres, these being capable of expanding during the drying step.
3. Process for the production of sheets of board, at least one of the faces of which possesses non-slip properties, according to either of Claims 1 and 2, characterized in that the sheet of board (21) after the drying zone is cut (25) to a controllable size and then stored in a stack (26) whose height can be adjusted.

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