US2031035A - Method of making moistureproof paperboard and the like - Google Patents

Description

Feb. 18, 1936. c. G. DREYMANN 2,031,035

METHOD OF MAKING MOISTUREPROOF PAPERBOARD AND THE LIKE Filed Oct. 11, 1933 INVENTOR UNiTD STATES PATENT OFFICE METHOD or MAKING MOISTUREPROOF rsrsnnoanp AND THE LIKE Carl G. Dreymann, Pittsburgh, Pa... asaignor to Grant Paper Box Company, a corporation of Pennsylvania Application October 11, 1933, Serial No..693 ,110 3 Claims. (Cl. 154-40) This invention relates to the art of making to both, of the plies. The two plies, after coatcardboard, paper board, and the like, and is found ing, are brought together, with coated surfaces in a method whereby sheets of such material may in contact, between a pair of rolls, 8, 9. The pass be produced that are impervious to moisture between the rolls 8, 9 is of such width as to bring laden air in higher degree than can otherwise be the coated plies together along a progressive line 5 attained. of contact, without appreciable compression. A The accompanying drawing is diagrammatic second pair of rolls it, it is provided spaced at and it serves to show in side elevation the inan interval from the pair 8, 9, and between this strumentaiities by which the method 'is persecond pair of rolls the united plies come after 10 formed. Fig. I shows apparatus in the use of they have advanced through the intervening in- 10 which the method is performed more simply; terval. The pass between rolls ill, I! is of-less Fig. 11 shows apparatus for performing the methwidth than that between rolls 8, 9, and is of such ad with refinement in detail. width as to compress the advancing material and It is common practice to make multiple-ply consolidate it into the finished product.

15 paper and cardboard by facing two component The adhesive that I employ may be one of the 15 sheets with thermoplastic adhesive in liquid state moisture-proof adhesives commonly employed for and bringing the coated sheets together, coated such purpose. It is, in my practical procedure, face to coated face, under pressure; and, in the a resin-containing adhesiv Adhesiveness is, to practice of this invention, the procedure so genbe sure, its characteristic; but, primarily, and

29 eraliy characterized is followed. The invention, essentially-with the success I contemplate in so however, is based on the perception that in parviewit must be a substance adequate to aiford ticular circumstances or conditions of operation a dam, a practically impervious wall, against lie causes and reasons, why the procedure as compenetration by moisture. The material that I monly pursued is relativehr ineffective to proemploy may,.typically, be a resin modified by a duce an article that is truly resistant to moisparafifln, in a compound that, after liquefaction 26' ture-laden air; and consists in such departure by heat, stiflens at 65 to 80 C. from and such addition to the usual procedure, in The paper or pressboard as it advances betweenrespect to details, as to afford the desired superior rolls 3, t and 5, 6 is at room temperature; such product. an adhesive as I have indicated may be applied 30 I have perceived that the effectiveness of the when at a temperature of 110 0.; the adhesive 80 adhesive as a screen and dam, preventive of the l is in the roll-passes 3-& and 5-6 spread upon passage of moisture-laden air, is in the usual the paper or pressboard in a coating or coatings practice seriously reduced and impaired by its that are heavier than such coatings ordinarily penetration into and its impregnation of the subare. In consequence of contact with the relastance of the sheet of board or paper to which tively cold paper and in consequence of the heavit has been applied. For, proportionately as it iness of the coating, the adhesive, though it gains disseminates into the interstices of the fibre, it firm anchorage, is not completely absorbed in the tends to lose continuity, and minute gaps or pinporous substance, but continues as an uninterholes or pores tend to open through the impregrupted film upon the surface of the supporting nated surface or surfaces; and I have further web of paper or board. In the roll-pass 8-9 the perceived of the usual practice that, in consesurface of the film or films is still relatively hot quence of the pressure applied to unite the plies, and fluid; and in this pass the parts of the ultiplastic adhesive is squeezed out from between the mate product are integrated. Particularly when progressively meeting surfaces; and, consequently, both plies bear coating films of the adhesive, the

the remaining material is not sufiiciently effectwo films merge in roll-pass 8-9 in a single in-' 45 'tive as a preventive of moisture penetration. tercalated film. The coating. films are, on their The first feature of the method of my invenmeeting faces relatively hot and fluid, and betion is that the uniting of the piles is a twotween these rolls 8, 9 the films meet along a prostep procedure, instead of the usual one-step progressive line of contact and merge.

cedure. Referring to Fig. I of the drawing, two The second pair of rolls I 0, II is spaced at an 50 plies of paper or thin cardboard I and 2 (one interval of a few feet (an interval related ob-- may, for example, be a ply of paper, and the other .viously to the speed of operation) from rolls 8, of board) are between rolls 3, 4 and 5, 6 coated 9-an interval sufflcient to'allow the radiation with a thermoplastic substance 1. The coating of heat to bring the combined film of adhesive is thus applied certainly to one, and preferably between the piles toapproximate the temperature 55 hesive, its viscosity at of stiffening, Under the pressure exerted by rolls l0 and l I the now semi-hardened adhesive will not be squeezed out from between the plies, but the multiple-ply article will be compressed and consolidated. A multiple-ply sheet is formed. in which is included an intercalated continuous film of a material that resists and prevents penietration b-y moisture-laden air.

The moisture-proof adhesive is applied to the sheet in a heavier layer than heretofore practiced; and the temperature of the adhesive is kept sufliciently low to prevent undue absorption by the fibers, but sufficiently high to keep it in a fiuid condition, so that the two coated surfaces when brought together flow into each other without the need of being subjected to pressure. This is efiected by passing the two sheets initially between the two rolls 8, 9, whose distance isequal to the combined thickness of the two sheets and the two coatings.

The adhesives which I have been using congeal at a temperature that varies from 65 to 80 C.; and, since the sheets to which the adhesive is applied are of room temperature, it takes only a few seconds before the coatings lose their fluidity. At the moment congealing sets in, and while the adhesive is still in a plastic condition, the plied board is, between rolls l0, ll, subjected to a second and slightly heavier pressure, which unites the two coatings more firmly, densifies their structure, and closes up any pinholes that may have been formed during the coating operation.

The effectiveness of this procedure is best 11- lustrated by a comparative test of the amount of moisture that passes through a ply-board made by the known procedure and one made in accordance with the present invention. A cardboard made under the most favorable conditions by the 01d process lets pass from 95 to 105 milligrams of moisture per 1000 square centimeterhour, whereas a board made with the same adhesive by my two pressure system lets pass only 10 milligrams per 1000 square centimeterhour, when tested in a. chamber which was maintained at 35 C. and 100% moisture.

Excellence of result requires, necessarily, operation under optimum conditions, and these conditions have to be set up empirically, since there is variation in particular cases. In order to obtain a continuous film oi suflicient thickness to give maximum protection against passage of moisture-laden air, and at the same time properly to unite two sheets of paper or board, the following factors have to be brought into harmony, namely: temperature of the moisture-proof adthe time of coating, its

I congealing point, the speed at which the sheet material is coated, the porosity of the sheet material, the time interval between plying the material and the application of the final pressure.

A slight change of any one of these factors ne cessitates a correction of the other ones. These familiar with the behavior of colloids in general, and of resinous materials, adhesives and moisture-proof materials in particular, will be able to determine such optimum conditions, in order to accomplish the ends described.

Without departing from the practice of the method in its essence, it still remains possible by heat applied (in relatively low degree) to rolls l0 and H, or to one or them, to vary the V denseness and compactness of the finished article.

Turning to Fig. II of the drawing, a sheet of paper laisimpregnatedwithasubstanceorm ftor example, it

pound (in fluid condition) that is impervious to moisture-laden air. The sheet may be of absorbent or of non-absorbent nature, according to the type and quality desired of the finished product, and according to the character of the moisture-proof substance used. The operation of impregnation is diagrammatically indicated. The sheet passes through a. bath I4 of the impregnating substance in fluid condition, and as it rises fromthe bath it passes between stripping rolls [5 and I6; thence, with a proper burden of the impregnating substance, it advances to the pass between rolls 8 and 9. This impregnation is, it W111 be perceived, a thorough one, so that no appreciable voids can remain within the impregnated sheet. And the stripping rolls l5, l6 are so set that the sheet i3 is but the carrier of a continuous film of the impregnating substance. In the pass between rolls 8 and 9 the sheets of paper or thin cardboard l and 2 are brought progressively to surface contact with the impregnated sheet [3. The two sheets I and 2 may or may not, preliminarily, have been coated in the manner already described. In case they have been so coated, the coating material may be the same as the material with which the sheet I3 is impregnated; or, if not, it will be an adhesive compatible with such impregnating material. And, generally speaking, the material with which the sheet I3 is impregnated, has the characteristics already indicated to be pussessed by the material I, and it may, indeed, be precisely such material. I

Between the rolls 8 and 9 the components are united, without squeezing and without exudation, as in the case already described. The material advancing from roll-pass 8-9 to roll-pass l0-I 'I gives up heat; the content of impregnating and coating material comes approximately to the temperature at which it sets; and then, between rolls l0 and H, the components are consolidated. And from the roll-pass the finished sheet advances.

The advantage of using a centre sheet impregnated with the moisture-proof material (the particular procedure illustrated in Fig. 11) is that it offers a simple means to apply the moistureimpervious material in a thicker layer, without the danger that the fluid material may run away, or be squeezed out when passing through the rollers. The board thus produced has greater stiflness, and can endure rougher treatment. It, be employed to form cartons for breakfast food, it will under creasing and bending operations be And cracking must for such use be prevented, for through cracks moisture will find paths of penetration.

In following the specific procedure described in connection with Fig. II, not only do I obtain a layer of the moisture-impervious material of always the same thickness; but, since the fibers oi the paper exercise a capillary attraction towards the material with which it is impregnated, the viscous moisture-impervious material is kept in position as it it were solid. As a consequence, the temperature of the impregnated material can be kept somewhat higher than otherwise would be possible, and this in turn insures a more perfect union with the two sheets between which it is intercalated. By varying the thickness of the centre sheet, and by employing in its preparation paper that is more or less absorbent, I have a stronger to resist cracking.

simple means for regulating the thickness 01' the moisture-resisting layer and therewith the degree to which the cardboard becomes impervious to moisture-laden air. In both cases there will be round in the finished article, between the plies, a layer oi. the impervious adhethousandth of an inch thick. Irdinarilmit will be of greater thickness than that-two to three onethousandths, i'or example.

It will be remarked that in both operations that illustrated in Fig. I and I claim as my invention:

l. The method herein described of forming a multiple-ply sheet of moisture-repellent cardboard, paper-board, and the like, which consists upon two plies of pain hot and fluid condition, merging of the films into thereby eflecting the a single film interto the point or stifiening oi the film material, and, finally, at such temperature, subjecting the article to consolidating pressure.

. 3. The method herein described of forming a multiple-ply sheet of moisture-repellant cardboard, paper board, and the like, which consists terial to cool, and at a temperature approximating that at which the adhesive sets rolling the material under pressure. T CARL G. DREYMANN.

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