US1960176A - Process of making and utilizing sheeted adhesives and the products thus produced - Google Patents

Description

Patented May 22;;119342 UNITED STATES PROCESS OF MAKING AND UTILIZING SHEETED ADHESIVES AND' THE PROD- ,.UCTS THUS PRODUCED Josef Weber and Franz Hengstebeck, Essen- Ru'hrgGermany, assignors, by mesne assign ments, to Th. Goldschmidt Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application June 2, 1931, Serial No.

541,734. In Germany February 2, 1929 7 Claims.

This invention relates-to processes of making and utilizing sheeted adhesives and to products thus obtained; and it comprises as a new adhesive articlea substantially dry, substantially homogeneous, thin flexible sheet of an alkaline con-- densation product of formaldehyde with a phenol, said sheet ordinarily containing a tenuousfiber reinforcement and said product being solid at ordinary temperature; becoming plastic and melt- I 0 ing when, warmed and setting to a hard permanent infusible form at temperatures somewhat above 100 0.; audit alsocomprises processes of making said adhesive articles and it further comprises methods of utilizing said new adhesive article and products so obtained; all as more fully hereinafter set forth and as claimed.

In the usual method of cementing wood to wood, including afiixing veneers-and making plywood,

the surfaces are treated with a solution, of glue 0 and setting performed under heat and pressure;

Setting is really a removal of water and where extensive surfaces are united, the water is taken up by the wood. Most liquid glues contain large proportions of water and in making plywood,.the

amount of water to be dissipated in the glue used may be as high as to per cent of the weight of the wood to be joined. In building up plywood assemblages, the glue is applied toinner layers and the water is taken up by proximate 30 layers thereby necessarily swelling these. At this stage in the operation the product includes a.

swollen inner wood layer connected to lessmoist outer layers or plies. In drying, the swollen inner layers tend to shrink to their original proportions thereby setting up heavy stresses and causing warping. Making plywood in this manner by the assemblage of successive laminae of wood with intermediate drying is a tedious operation and the product is apt to be irregular. The whole assemblage must be finally dried and unless this. final drying, as well as the intermediate dryings, be conducted with-exceptional care and skiilan unsatisfactory product results. It maybe warped, mottled or exhibit fissuresiincipient cleavage). In order to obviate these diiiiculties it hasbeen proposed to manufacture. plywood and afiix veneers by employing between the layers of wood a cementing layer in the form of glue-surfaced sheets of paper, of fabric, or even of wood. In making the cementing layer, suitable sheets are passed through a glue solution and afterwardsdricd so as to form adhesive surfaced sheets adapted to be interposed between the wood plies. Using sheets of this character the amount of water necessary can be limited to that required to make the surface of the sheets sticky; and this is an advantage. This method while better, than the more common procedure of cementing by liquid glue directly applied is nevertheless open to certain objections. For one thing in the final product, there is anintermediate structural element between the wood plies. For anothenply-e.

wood made in this manner when subjected to changes in temperature and moisture conditions frequentlytends to split apart along the plane of the intermediatefabric layer; the layer. carrying the glue on its surfaces. Unless the glue is waterproofed in some manner, the.dried layer is not resistant to the action of moisture.

In afiix'ingveneers and in making plywood it is desirable to havethe wood layers as close together, face to face, as possible, restricting the amount of intermediate adhesive to that sum-,- cient to even out surface irregularities. And it is desirable to have an adhesive. requiring in setting the dissipationofno great amountof water or of a volatile solvent; of any amount causing substantial swelling in the wood. These results are accomplished in the present invention where- V in is provided a thinsubstantially dry, substantially homogeneous lamina of adhesive usually containing a tenuous fiberreinforcement in negligible amount; the adhesive being .solid at the ordinary temperatureQsoftening andfusing to a mobile liquid at higher temperatures and finally setting to a hard infusible, permanent form on exposureto temperatures such. as are used .in making plywood, say at 130 Ca For our purpose we use a particular condensation product of a phenol and formaldehyde in the presence of a rather large amount of alkali; this alkali serving both as a catalyst in inducing condensationand having Icertain otherfui'iticns. As the phenol, ordinary'phenol may be used or one ofthe cresols. In'lieu of formaldehyde, acetaldehyde or other aldehydes may be employed. However, ordinary phenol and ordinary formaldehyde, as the commercial 40 per cent solution, givegood results. On dissolving equivalent amounts of phenol and formaldehyde (in solutionlin 40 per cent caustic soda lye using the amount of lye necessary for solution, a satisfactory,preparation can be made-for the present purposes. With a batch of 94 kilograms of phenol and 100 kilograms of commercial 30per cent formaldehyde solution about 17 kilograms of 40 per cent NaOH solution give a good -preparation. This liquid is 'kept' warm. for a time say at 80 C. for 1% hours, with constant stirring until an easy flowing oily dark liquid is obtained.

Heating must be stopped before an aqueous layer separates from the reaction products. The separation of such a layer 'shows that the reaction has gone, too far and the condensation product obtained will not possess the advanta geous properties here desired. The viscosity of the product obtained depends upon the time of heating but is rather low in any event. The exact viscosity desired can be obtained by interrupting the heating and then cooling. Because of the solvent infiuence of the excess of alkali and of the water present, noseparation into two layers is produced. The oily liquid can be dried to a substantially dry material at temperatures below about 100 C. without going into the final insoluble resin. Ordinarily it is desired to dry the material to about 2 per cent water. By proper manipulation the dried material may be made in thin sheets. These sheets at the ordinary temperature are not tacky but are somewhat hygroscopic in the sense that they will take up morev water from the air. Ordinarily the amounttaken up will give a final product of'about 5 to 8 per cent; this varying with the humidity. With this content of water the product is flexible and not sticky or tacky andthe sheets can be packaged, shipped and stored as rolls without danger of adhesion.

As so far described, the sheets are made without the use of a reinforcement but for manufacturing reasons it is better to employ a tenuous reinforcement of fiber in negligible amount; an amount insufficient to produce a substantial intervening layer between the sheets of wood ultimately to be united. As'this'reinforcement we employ an open textured, thin paper, or like sheeted material. With the aid of this paper it is possible to produce the present material by ordinary manufacturing operation in a continuous manner; a web of paper passing first through the initial condensation product,'past equalizing rolls .and then through drying apparatus. Drying is usually so conducted as to give about 2 per cent water in the dry material and sufficient exposure to air is then permitted to allow assumption of the full amount of water of condition; usually about 8 per cent. The proportion of fiber to adhesive varies but is usually in about the ratio of 1 2. With thin open textured'pa'per in this proportion the final sheeted product has a substantially continuous body of adhesive. In making such completely and uniformly impregnated sheets which are in fact continuous films of adhesive, the thickness and porosit'yor open texture of the reinforcing sheet are so correlated with the liquidity or'yiscosity of the oily liquid condensation product containing caustic soda as to insure a-complete, continuous and uniform impregnation. When this relation is properly established the oily liquid penetrates all the poresof the reinforcing medium and .it is only necessary to apply the proper amount of liquid to "give the is not tacky; is not hygroscopic enough to become moist and sticky in ordinary air. It does however take up a littlewater of condition; enough to make it flexible and easily handled. The dry composition on warming to a few degrees above the ordinary temperature becomes plastic enough to facilitate easy sheeting and on recooling is permanent; it can be stored, packaged and handled without trouble. In heating to fusion in .use, probably the caustic soda and the small reaches a point somewhere around 130 C. when the catalytic action becomes extremely rapid. In the. final product the caustic soda does not exist in any form making the article hygroscopic;

nor is it necessary in making plywood to provide for the dissipation of the water present in the mixture. It is, in any event, small in amount being only about 5 to 8 per cent of the adhesive.

When the fiexible sheeted adhesive (with or without reinforcement) is placed between two layers of wood in the usual way of aflixing veneersor making plywood and heat and pressure are applied, the adhesiveat first yields and softens. then fuses and is then taken up for the most part by the pores of the wood; finally solidifying in place. With about '8 percent water in tlie material on fusing it forms afairly mobile liquid readily taken up by pores as a whole; there without much change in volume and with very little extrication of water; not enough to cause swelling or require any special care in subsequent drying.

Because of the propertiesof the present adhesive sheet it is possible to join a number oi. layers of plywood. together simultaneously instead of successively as is the usual practice; thereby economizing time and labor.

While the invention'has been particularly described in its use in cementing veneers and making plywood, the adhesive sheets of the present invention are advantageous in manyother relations and may beused for general cementing purpose. Their use in forming a. facing layer on various articles is advantageous.

What we claim is:

1. As a new product, adhesive papers for plywood manufacture comprising a porous open textured tissue paper sheet impregnated with an initial condensation product of an aldehyde with a phenol, said condensation product containing a. substantial amount of alkali, being capable of softening and fusing under heat and pressure to give a mobile liquid, being capable of hardening under said heat and pressure to give a hardened insoluble body, and having been produced at low temperatures in a dilute causticalkali solution without separation of an aqueous layer.

2. As a new product, adhesive papers for plywood manufacture comprising a porous open textured thin tissue paper sheet impregnated with a. low temperature, initial condensation product of an aldehyde with a phenol, caustic soda, and a small amount of water fixed as water of condition, said water being about 8 per cent of the total adhesive, the ratio of said condensation product to the paper being about 2:1.

3. A process of making adhesive papers for plywood manufacture which comprises heating formaldehyde with a phenol in an aqueous solution of caustic alkali under conditions suitable for producing a homogeneous, easy flowing, oily in itial condensation product without the separation of an aqueous'layer, impregnating a porous, open textured tissue paper sheet with said product without the presence of extraneous solvents and drying to produce a non-tacky surface.

4. In the making of adhesive papers for plywood manufacture, the process which comprises warming a phenol and formaldehyde together in the presence of an aqueous caustic soda solution under conditions suitable for producing a homogeneous oily, liquid condensation product without the separation of an aqueous layer, and impregnating a porous, open textured, thin tissue paper sheet with said product and drying the im pregnated paper, thevamount of alkali present not being suiiicient to give the dried sheet a tacky surface but being suflicient to cause absorption of from about 5 to 8 percent of water of condition on exposure to air.

5. In the making of adhesive papers for plywood manufacture, the process which comprises reacting together an aldehyde and a phenol in an aqueous solution of caustic alkali under conditions suitable for producing a homogeneous, oily, liquid, initial condensation product without separation of an aqueous layer, impregnating a porous, thin tissue paper sheet with said prodnot and drying the impregnated sheet at temperatures below about 100 C. to form a substantially dry, solid but flexible sheet containing a substantial amount of caustic soda and water of condition; the impregnating condensation product being capable of assuming a highly fluid state under heat and pressure at temperatures not substantially above 130 C.

6. As a new product, an adhesive sheetlfor plywood manufacture comprising a porous, open textured, tissue paper sheet impregnated with an initial condensation product of an aldehyde with a phenol, formed without separation of an aqueous layer and in the presence of a caustic soda solution, and containing a small amount of water fixed as a water of condition, said water being about 5 to 8 per cent of the total adhesive; the said condensation'product being free from extraneous solvents, being capable of assuming a highly fluid state under heat and pressure at temperatures not substantially above 130 C. and, when placed between sheets of plywood and subjected to heat and pressure, being capable of fusing to form a mobile liquid and then hardening in situ to unite said sheets with a hard, insoluble bond.

7. As a new product an adhesive sheet for plywood manufacture comprising a porous, open textured, thin tissue paper sheet impregnated with a low-temperature, initial condensation product of an aldehyde with a phenol formed in the presence of a caustic alkali solution, the said condensation product being free from extraneous solvents, being capable of assuming a highly fluid state under heat and pressure at temperatures not substantially above 130 C. and, when placed between sheets of plywood and subjected to heat and pressure, being capable of fusing to form a mobile liquid and then hardening in situ to unite said sheets with a hard, insoluble bond.

JOSEF WEBER. FRANZ HENGSTEBECK.