US3357877A

US3357877A - Method of stiffening the corrugations of corrugated cardboards and the resultant prodct

Info

Publication number: US3357877A
Application number: US335128A
Authority: US
Inventors: Gandon Louis
Original assignee: Nobel Bozel SA
Current assignee: Nobel Bozel SA
Priority date: 1963-01-09
Filing date: 1964-01-02
Publication date: 1967-12-12
Anticipated expiration: 1984-12-12
Also published as: FR1356282A; GB1056711A

Description

3,357,877 ATED Dec. 12, 1967 GANDON METHOD OF STIFFENING THE CORRUGATIONS OF CORRUG CARDBOARDS AND THE RESULTANT PRODUCT Filed Jan 1964 United States Patent 9 Claims. Cl. 161-133) The present invention has for its object a method of stiffening the corrugations of corrugated cardboards, said method being characterized essentially by the treatment of the papers to be corrugated with an aqueous solution of glyoxal containing guar gum and a condensation catalyst.

In order to make the nature of the present invention more clearly understood, there will first be described the mechanical aspect of its execution, this aspect being shown diagrammatically by the accompanying drawings.

FIG. 1 shows a corrugated cardboard which comprises a corrugated paper 1 known as a corrugation or wave on each face of which is stuck a non-corrugated paper, namely the outer cover 2 and the inner cover 3. During the manufacture of a cardboard box, the said covers are located on the outside and on the inside of the box, respectively.

In a composite cardboard of this kind, the part which is at the same time the most important and the most difficult to produce is the rigid corrugation. This corrugation, although made of paper, must in fact have sufilcient resistance to crushing when laid flat so that it can be employed for the manufacture of boxes or cases of corrugated cardboard used for packing articles of the most varied kinds.

Corrugated cardboards used in practice for the manufacture of such packing cases may be either simpler or more complex than that shown in FIG. 1, which is known as double corrugated cardboard, but they all comprise the said rigid corrugation and at least one covering sheet stuck on it, it being always essential for the corrugation to have the maximum strength to crushing when flat. Thus, there are also used for example simple corrugated cardboardsf (comprising but one corrugation and one cover); double-double corrugated cardboards (comprising an outer cover, a small corrugation, a central corrugation, a large corrugation and an inner cover); triple corrugated cardboards, etc.

For the manufacture of a simple corrugated cardboard according to the method of the present invention, the

mechanical operative-steps shown diagrammatically in FIG. 2 will preferably be carried out: a sheet of paper supplied from a roll 4 of straw-paper for example, moving forward at a uniform speed in the direction of arrow 5, is wetted at 6 with the said aqueous solution of glyoxal containing guar gum and a condensation catalyst. The sheet of paper then passes over a heating drum 7 and then between two corrugating cylinders 8 (toothed wheels). The heating produces a thermal plastification (as in the case of a permanent wave) and the paper comes out in the corrugated state after passing between the two cylinders.

The said corrugated rigid paper (corrugation) passes over a cylinder 9 rotating in a bath of an adhesive agent 10; it is then coated with the said adhesive (of silicate for example) and finally during its passage over a heating drum 11 meets the sheet of paper which is to serve as a cover, supplied from a roll 12 of paper; the cover sheet is thus stuck on the corrugation, the heating at 11 accelerating the setting of the adhesive agent.

It will be understood without further explanation that by the same process it is possible to stick a second cover sheet on the other face of the corrugation, or alternatively to manufacture double-double or triple corrugated cardboards, etc.

The mechanical process having thus been explained, the nature of the invention will be illustrated in a more detailed manner.

In known methods, water is generally used for the impregnation of the paper to be treated. There is thus obtained a corrugation whose resistance to crushing when flat (which is a measure of the stiffness) is fair, but which, in the damp state, has only a quite poor rigidity or stiffness, which is a great practical drawback. In fact, corrugated cardboard boxes manufactured with such corrugations cannot be employed as packings for certain kinds of food products, such as fruit, vegetable, etc., which breathe, that is to say which create an atmosphere saturated with moisture. Under the action of humidity, the resistance to crushing of the corrugations falls to an insufiicient value and the packing of corrugated cardboard collapses, which makes it unsuitable for this kind of use. The problem of behaviour to moisture also presents itself for example during transport over long distances by sea.

Now, the production of a cheap packing material for such uses in the field of corrugated cardboards meets at the present time a pressing need in the industry.

The known methods for improving the resistance to water of papers such as those which serve as cover sheets in the manufacture of corrugated cardboard, do not provide any solution to the problem as set hereabove. In fact, it is the central corrugation of the corrugated cardboard which must have the requested properties of stiffness and resistance to water; the properties of the cover sheets being of minor importance; in addition, it is necessary to have a simple and inexpensive method which, furthermore, should neither modify nor complicate existing installations.

The products generally employed for sufiiciently improving the mechanical properties of paper (e.g. thermosetting resins) are not suitable in this case since paper pre-treated with such products has no thermo-plasticity and breaks when it passes between the two corrugating cylinders 8.

An attempt has been made to cope with this drawback by the use of thermo-plastic resins, more particularly polydiene resins, for the prior impregnation of the paper to be corrugated. However, such a method is not applicable in practice on a large scale. On the one hand, the necessity of utilizing a volatile organic solvent in order to distribute the resin uniformly in the paper, is already prohibitive, by reason of the large quantities of solvent which are liberated in the workshop or which have to be recovered by the use of complex and expensive installations; on the other hand, a paper treated in this way does not accept, when applied at the cylinder 9, enough of the usual adhesive agents intended to stick the cover sheet on the corrugation; it would be necessary to use special and costly adhesive agents under complicated conditions of use. The method of the present invention replaces at wetting position 6 the moistening water generally use, by an aqueous solution of glyoxal containing guar gum and a condensation catalyst; this method makes it possible to obtain, without in any way modifying existing installations, a considerable improvement in the resistance to crushing of the corrugations, both in the dry state and in the wet state.

For carrying out the method according to the invention the paper to be treated is impregnated with the said solution so that the quantity of solution retained by the paper corresponds to a weight of from 0.5 gram to about if: 10 grams of dry material deposited per square metre of paper, for example from 1 to 5 grams; then, the thus treated paper is converted to a rigid corrugation, preferably in the manner indicated above, which is shown diagrammatically in FIG. 2.

The preferred sequence of the operations is therefore as follows, in the case of a simple corrugated cardboard: impregnation of the paper by the said solution at wetting position 6 according to the invention; thermo-plastification by heaing such as with the heating drum 7; corrugation steps, such as deformation with the cylinders 8; coating at cylinder 9 with an adhesive agent and applying the cover sheet such as with the drum 11.

The temperature employed for the thermo-plastification has no influence whatever on the results which can be obtained by the present method, since the useful reaction already takes place when cold; it is thus possible to work at the usual temperatures of practice already adopted by the various factories already in operation.

Without departing from the scope of the invention, any other mechanical process of conversion of the impregnated paper to a rigid corrugation can be employed.

The aqueous solution to be used for the impregnation of the paper to be treated comprises, per litre, preferably between 20 and 200 grams of glyoxal expressed in CHO-CHO and, with respect to the glyoxal, preferably from about 10 to 50% by weight of dry guar gum and from about 2 to 8% of condensation catalyst.

For the preparation of the said solution, glyoxal may be employed in the form of an aqueous solution, or alternatively in the form of glyoxal polyhydrate in powder form.

The guar gum, which is a galacto-mannite gum chemically constituted of units of galactose and mannose, can be dissolved in the form of powder or after having been previously brought into the form of an aqueous solution. The various commercial kinds of guar gums can be employed, in particular the one having a very low viscosity (50 cp. at C., in a 2% solution).

The condensation catalysts to be employed are preferably acidic compounds or such as are capable of producing acids during the course of the treatment, such as the chlorides or sulphates of non-alkaline metals, for ex ample aluminum sulphate.

The order in which the various compounds are dissolved has no influence whatever on the results.

There may also be prepared a mixture of powders constituted by glyoxal polyhydrate, guar gum and the sulphate. There are added 200 grams of dry guar gum of very low viscosity cp. at 20 C. in a 2% solution).

This mixture is made-up to a volume of 10 litres with water, and then stirred until the solution is complete, which gives a perfectly clear solution.

A straw-paper having a weight of 140 grams per square metre is impregnated with the said solution, in such manner that the amount of solution retained by the paper corresponds to n grams of dry material deposited per square metre of paper.

Three operations a, b, 0, have been carried out in this way so as to deposit in the three cases the following quantities of dry material per square metre of paper:

Operation a: 11:1 g. Operation b: 12:33 g. Operation 0: n=4.8 g.

The impregnated papers are converted to rigid corrugations in the manner described in the present specification diagrammatically shown in FIG. 2.

In order to appreciate the qualities of the corresponding rigid corrugations, a sample of each of the three papers a, b and c was subjected to the standard test of the ring crush according to the standard of the T.A.P.P.I. (Technical Application Pulp and Paper Industry) 472 m 51, which provides a figure expressing the annular stiffness in lbs/inches, which stiffness represents the 0thcial test of resistance to crushing.

On each of the papers, test-pieces were taken in the machine direction and test-pieces in the cross direction; in each case, the measurements were made, on the one hand, on the dry paper and on the other hand on the wet paper. The dry paper is a paper conditioned for 24 hours in an atmosphere of relative humidity at 20 C., the wet paper was prepared by previous conditioning for 48 hours in an atmosphere having 90% relative humidity at 20 C.

An untreated paper, called a check-sample was examined under strictly identical conditions.

After having measured the resistances to crushing, the coefficients were calculated, that is to say the ratios of the resistances of the treated papers to the resistance of the corresponding sample paper.

Finally, the ratios wet/dry or W/D were calculated, that is to say the resistances to crushing of the wet papers, divided by the resistance to crushing of the corresponding dry check-sample, in percent.

The following results were obtained:

TABLE I Resistances to crushing Coefiicients Ratio W/D n Machine Cross Machine Cross (gJmfi) direction direction direction direction giaclzine d Cross irec ion irection Dry Wet Dry Wet Dry Wet Dry Wet (percent) (percent) paper paper paper paper paper paper paper paper Cheek sample 38 14 25 6 37 24 Operation ((1) 1 50 23 27 8. 2 1.32 1. 64 1.08 1.37 Operation (b).. 3.3 50 31 32 17 1.32 2. 32 1.28 2. 84 2% Operation (0) 4. 8 58 32 43 20 1. 53 2. 28 1. 72 3.84 84 80 catalyst. This product in powder form can be stored, transported, etc.; it will be put into an aqueous solution for carrying out the method according to the invention.

In order to make the invention more clearly understood, there will be given below, by way of illustration but without any limitation, a few examples of the method of execution and the results which can be obtained.

Example 1 In 5,000 grams of an aqueous solution of glyoxal at 30% by weight, there are dissolved 75 grams of aluminum Example 2 50 grams of aluminum sulphate is dissolved in 3,300 grams of an aqueous solution of glyoxal at 30% by weight. There is added 200 grams of dry guar gum having the following amounts of dry material per square metre of paper:

Operation a": n=1 gram Operation b": w=3fl grams a very low viscosity. 5 (See the table which follows.)

TABLE III [Results: 'I=check sample] Resistances to crushing Ooeificients Ratio W/D 11 Machine Cross Machine Cross (gJmfi) 2 direction direction direction direction Machine Cross direction direction Dry Wet Dry Wet Dry Wet Dry Wet (percent) (percent) paper paper paper paper paper paper paper paper Operation a: n=l gram Operation b: n=2.5 grams Operation c: n=4.7 grams By way of comparison, an operation E was made with a solution identical to the preceding one, but containing glyoxal and the catalyst only, and therefore no guar gum (3,300 grams of 30% glyoxal solution+50 grams of aluminum sulphate in 10 litres) described in the following table:

TABLE II The above examples have been given with guar gum, but obviously other galacto-mannites may be used such as, for instance, carob-gum.

I claim:

1. A paper impregnating and coating composition of matter consisting essentially of 10 parts by weight glyoxal, 1-5 parts by Weight guar gum and an acidic condensation catalyst selected from the group consisting of non-alkaline metal chlorides and sulfates.

2. A paper impregnating and coating composition consisting essentially of an aqueous solution containing from 20 to 200 grams per litre of glyoxal expressed as CHO-CI-I'O and, on the basis of the weight of glyoxal, from 10 to of dry guar gum and from 2 to 8% of an acidic condensation catalyst selected from the group consisting of non-alkaline metal chlorides and sulfates.

[Results (T=check samp1e)] Resistances to crushing Coefiicients Ratio W/D n Machine Cross Machine Cross (gJmfl) direction direction direction direction Machine Cross direction direction Dry Wet Dry Wet Dry Wet Dry Wet (percent) (percent) paper paper paper paper paper paper paper paper It is seen that the resistances to crushing of the papers reach values more than double and even more than three times those of the corresponding untreated papers and that the resistances to crushing of wet papers reach values close to or equal to that of the corresponding check sample of dry paper, which is remarkable.

It can also be seen that under the conditions of the present invention, the glyoxal with the catalyst alone, in the absence of guar gum, gives practically no improvement in the resistance'to crushing, either in the dry or in the wet states.

Example 3 In 1660 grams of an aqueous solution of glyoxal at 30% by weight, there are dissolved 25 grams of aluminum sulphate. There is added 200 grams of dry guar gum having a very low viscosity.

The mixture is completed to a volume of 10 litres with water and then stirred until everything is completely dissolved.

The procedure is continued as in Example 1, carrying out two operations, a" and b in such manner as to deposit the impregnated sheet, and heating the resulting corrugated paper, the improvement which comprises carrying out said impregnating and coating step using a composition consisting essentially of 10 parts by weight glyoxal, 1-5 parts by weight guar gum and an acidic condensation catalyst selected from the group consisting of non-alkaline metal chlorides and sulfates.

5. The improvement according to claim 4 wherein the amount of said impregnating and coating composition applied to said paper is from 0.5 to 10 grams on a dry basis per square metre of paper.

6. A composition in accordance with claim' 2 wherein said acidic condensation catalyst is aluminum sulfate.

7. A method in accordance with claim 5 wherein the amount of said composition applied, on a dry basis, is between 1 and 5 grams per sq. metre of paper.

8. A corrugated paper of high wet strength comprising paper impregnated with a composition consisting essentially of 10 parts by weight glyoxal, 1-5 parts by weight guar gum and an acidic condensation catalyst selected from the group consisting of non-alkaline metal chlorides and sulfates.

9. A corrugated paper in accordance with claim 8 wherein said impregnant composition comprises 0.5 to 10 grams per square metre of paper and the amount of the catalyst comprises 2 to 8% catalyst based on the weight of glyoxal.

References Cited UNITED STATES PATENTS 1,796,542 3/1931 Schoo 161-137 2,568,349 9/1951 McKee 161-137 2,644,750 7/1953 Frisch et a1 106205 3,228,928 1/1966 Opie et al 106205 3,276,885 10/1966 Gandon 106208 FOREIGN PATENTS 1,356,282 2/ 1964 France.

MORRIS SUSSMAN, Primary Examiner.

Claims

8. A CORRUGATED PPER OF HIGH WET STRENGTH COMPRISING PAPER IMPREGNATED WITH A COMPOSITION CONSISTING ESSENTIALLY OF 10 PARTS BY WEIGHT GLYOXAL, 1-5 PARTS BY WEIGHT GUAR GUM AND AN ACIDIC CONDENSATION CATALYST SELECTED FROM THE GROUP CONSISTING OF NON-ALKALINE METAL CHLORIDES AND SULFATES.