US2030819A - Process for preparation of leatherlike flexible and pliable material from wood sheets - Google Patents

Description

' loosening of the wood structure.

Patented Feb. 11, 1936 aoao ns UNITED STATES PATENT OFFICE 2.030.819 P122258 FOR ll'llEgANgATloN OF EATER- FLEX'IB FROM WOOD SHEETS Reginald Oliver Hersog, Berlin-Steghta, and Alfred Bln'genl, BerIin-Hchterfelde-West, Germany, assignors to Wallwood Corporation, New

York. N. Y., a corporation of New York No Drawing. Application December 3, 1930. Serial No. 499,846. In Germany December 5, ms

4 Claims.

The invention concerns a leather-like, flexible and pliable material from wood sheets or rods with retention of the natural wood structure and of the characteristic wood grain, as well as a process for its production and. manufacture.

The sphere of application of such products lies preeminently in the preparation of non-splitting veneers, wall coverings, furniture upholsterings, roll shutters, fancy goods and various containers. In all of these cases it is necessary to have completely plane working pieces, which may be coated and glued. By the following process it is possible to manufacture a material which satisfies these requirements in all respects. The method consists in a chemical softening, a treatment for the stabilization of this softened condition, a treatment with film-building colloids and possibly a mechanical treatment.

I. Chemical softening It is possible to transform thin wood sheets or woods into a soft, flexible condition by all processes for cellulose production, so long as the treatment is not extended too far. Especially good results may be obtained by the alkali softening, which results in a thorough swelling and The soft flexible structure, however, only lasts as long as the wood contains enough water. It gradually loses these properties by air-drying, and the dry product finally again becomes hard and brittle.

II. Preservation of flexibility impregnated with materials of low vapor pressure which are suited to stabilize the condition of loosening and swelling. Experiments have shown that two groups of substances come into consideration for such an impregnation. The first group contains substances of low vapor pressure which are water soluble and perhaps water attracting, such as glycerol, monoacetin and lactates. These substances act themselves as swelling and softening'preservatives. Since it is necessary to introduce large quantities of these materials into the wood in order to retain it in a sumciently soft condition, this sort of impregnation is rather expensive. The second group contains water insoluble but emulsifiable substances, such as liquid, dissolved or emulsified hydrocarbons, fats, oils and soaps, known emulsifying agents, such as sulphoand oxyfatty acids and their derivatives (Turkey red oil, or similar products such as alkali salts of sulfonated castor oil) To be sure, the substances of the second group work asretainers or softeners on the softened wood, still their effectiveness is largely dependent on moisture content of the material. Thus, a softened board, treated with wool fat soon becomes hard and brittle when put in warm, dry air. It was, however, found that very good results might be obtained by using plastifiers of both groups, as then even in dry air the plastifying action of both groups, which in each case has a different cause (group It acts mostly through swelling, group II through lubrification) work together. An instance of such impregnation, which makes possible an important reduction of manufacturing costs and at the same time an improvement in the product,,will be given later under sample applications.

It was further settled by experiment that for the production of products which are plane and at the same time suitable for gluing and lacquering, it is necessary to avoid transformation of the cellulose into cellulose hydrate, both during the alkali softening (which will usually come into question) and during the followingimpregnation. x-ray tests of the wood samples serve g The transformation of native cellulose into cellulose hydrate involves a shrinkage of in the fiber direction, and this is a substantial ground why the originally fiat veneers or slats warp, and the wood grain shows in relief, owing to the inhomogeneity of the material. If solutions of strongly hygroscopic materials, such as zinc chloride (which itself brings about the transformation of the native wood cellulose into cellulose hydrate) are used, the inequalities of the wood disappear somewhat. Still, such a product, by

reason of its high moisture content, may be neither glued nor lacquered, and is besides unstable because of its acid reaction. Therefore it is not usable for the above purposes.

For the production of working material of the above named properties it is not only necessary that, by preventing formation ofcellulose hydrate, no shrinkage in the fiber direction occurs, but that the shrinkage perpendicular to the fiber direction he reduced as much as possible, which may be obtained by suitable composition of the impregnating liquid. For many purposes it is sufilcient to use an impregnation with a suitable concentration of a solution of a plastifier of the first class, e. g.,, impregnation with a 35 vol. percent glycerol solution. (If the concentration is much below 35%, there results shrinkage and insuiiicient plastifying action; if much above, the material is unsuited for further work because of its hygroscopicity.)

Very suitable, however, is an impregnation with a combination of plastifiers of both groups, for example. with glycerol and soap (see sample application). In this case shrinkage is entirely avoided and 40%-50% of the glycerol which otherwise would be required is saved. In general, it was made evident that shrinkage in the direction perpendicular to the fiber direction and 9., though small, saving in glycerol would be obtained if non-volatile fillers were added to the glycerol-water mixture, even if these fillers had in themselves no softening action. Thereby the vapor pressure of the solution is reduced, and a greater weight of the mixture is in equilibrium with the surrounding atmosphere than in the case of pure glycerol impregnation of the above concentration. It follows therefrom that a. part of the glycerol may be spared. Starch sugar, invert sugar, and organic combinations, etc. can be used as fillers. What is here said for glycerol applies equally well for the other usable plastiilers. The following operations, gluing of a support and lacquering, are made easier if the impregnating bath contains additions of colloidal lyophile' substances such as starch, dextrine, pectin, gelatine,

etc.

Example methods 1. Linden wood veneers one millimeter thick are treated, 6 hours with cold 4% caustic soda, washed, bleached by the usual methods (oxidative and reductive) to the original lightness, thoroughly washed, impregnated with a 35% by vol. solution of glycerol in water until saturated, then dried in the air. Each kilogramme original weight of wood takes up about 600 grammes glycerol.

2. Maple, oak and pine and other woods which are diflicult to soften are treated three hours cold and 12-16 hours with boiling 4-8% caustic soda and then further as in (l) 3. Colored wood, such as walnut, mahogany, etc. of 0.5 mm. thickness, is softened as in (1), bleached with 2% oxalic or sulphuric acid, and further treated as in (1).

4. Linden veneers are softened as in (1), and bleached, then treated in a shaking machine 24 hours with a solution containing 20% by vol. glycerol and 80% by vol. of a mixture of an alkali salt of sulfonated castor oil and water in the ratio of 1 :2, then air dried.

5. Linden veneers are softened as in (1), and impregnated with a solution of 20% glycerol, 25% glucose syrup (43 B.), and 25% water. A small quantity of antiseptic is added to the bath.

6. Linden veneers are softened as in (1),

bleached and impregnated with a solution of 35% glycerol and 10% dextrine in water. antiseptic must be added to the bath.

III. Treatment with film forming colloids A little by treatmentwith elastic film forming colloids.

ic acid, glue, gelatine, cellulose esters and physically similar substances are suited for elastic film building colloids. The treatment with these substances may occur either through impregnation or on the smface.

Polyvinyl acetate and polyacrylic acid have a great advantage over the physically similar cellulose esters, in that they are more hydrophile,

whereby for example an adherent coating may be made on relatively moist wood fibers.

The impregnation may be either performed by the usual methods with a solutionof the colloid (with or without the addition of plastifiers), or else polymerizable substances, such as vinyl ace tate, acrylic acid, etc. (with or without addition-of plastiflers) may be soaked up in the wood and there polymerized in the known manner, for example with catalyzers.

The impregnation with film forming colloids can in certain instancesoccur in connection with the plastifying stage describedunder-II. I

It is possible in some cases to replace the expensive and diflicult impregnation with film building colloids by brushing, dipping or spraying so that only a surface coating is formed.

At the same time, this coating acts as a lacquer, whose thickness is chosen to correspond with the awaited conditions of service, and, for the sake of convenience, we shall claim the abovementioned substances as lacquers. In certain cases, where severe mechanical forces do not have to be withstood, as in wall coverings, this coating serves only the purpose of a varnish.

IV. Mechanical working It is advantageous at some time before, after or during the above described process to give the wood sheets a mechanical working in calenders or perhaps presses, whereby the pliability of th material is considerably increased.

Example methods brushing, dipping or spraying on one or both sides and then a coating of nitrocellulose lacquer is put on. Highly polymerized vinylacetate is especially suitable for brushing or dipping, while the lower polymerization grades are better adapt-' able for spraying.

9. The softened sheets are (possibly after washing out the water with methanol) impregnated at under a pressure of 5-20'atmospheres with a solution of -150 g. gelatine or glue, 350 g. glycerine and 600-700 cc. water. After this the gelatine or glue ishardened and the surface in the usual way with formaldehyde or alum solution. After thorough drying the sheets are given a thinlacquer coating.

' 10. The sheets softened and impregnated according to Examples 143 are laid for a short while in a solution of 120-150 g. gelatine, 250 to 450 g. glycerine and 600-700 g. water heated on the water bath, hardened and further treated as under (7) V. Gluing of a support There is a large field of application for soft and pliable wood sheets, when they are united to a textile base according to our invention. The material worked by the method described has comparatively little tensile strength perpendicular to the fiber direction. For certain purposes it is therefore desirable to glue it by a further process (usually after the impregnation with softening agents) to a flexible support. Such a compound sheet consists of an upper layer of pliable wood and an under layer of. felted fibers, films or fabric of any sort. In some circumstances a metal clotlror sheet can serve as under layer. Also, pliable wood itself can be used for the support, the layers being either parallel at, an angle to each other.-

The pliable wood and the textile base are combined by means of an adhesive. It may be-advantageous in case of some varieties of impregnating material to provide a protecting coating impervious to water and to impregnatebefore to one another. or

gluing. Also, the protective coating and'the ad-,

hesive can be one and the same material, such as polyvinyl acetate, cellulose esters (such as celluloid-like glues) and physically similar substances.

many slats not only increases the weight, but.

also causes a noisy operation and is unsatisfactory on aesthetic grounds, because the grain peculiar to the wood and especially desired in furniture is not properly brought out. These disadvantages are not observed when using the new material. Indeed, itofiers new advantages, if the roller axis is perpendicular to the grain. Thereby the growth characteristics of the wood are used in'the best manner, as then the direction of greatest strength falls in the direction of the hardest requirements, and even by repeated alternating loads plastic deformation is avoided and the wood is not deformed in fiber direction. The material is in this regard better than artificial leather, which is plastically deformable in every direction when alternately loaded and unloaded.

The wood layer may be provided with openings of any desired form, in order, for example, to let air through for heating or ventilating purposes.

This is not hindered by the cloth support. Such openings also make the material suitable for coverlngs for musical instruments, loud speakers, etc.

Our veneer after softening and mounting on a support, possesses the advantage over the known plywood of.thin veneers of a greater resistance to separation of the layers, especially after repeated bending and folding strains, and it is incomparably more pliable. As a result, the material is suitable for floor-carpets, stair-carpets and the like; covering for flat or curved surfaces, for example, as wall covering, non-splintering grain of the upper and lower.

Gil

Compound sheets may also be made in which i one or both sides have been covered with films (e. gJCell'on films). Such materials are'suitable, for example, for unbreakable ords.

phonograph rec- As already mentioned, the wood sheetsafter softening and being made pliable are suitable either alone or in combination with a textile base as covering for plane or curved surfaces. The

compound sheets are very suitable for wall coverings, as they may be madse in rolls of any desired length and width and applied to the wall in the same manner as wall-paper. Still, correspondingly large pliable veneer sheets without support can find use. In some casesthe unlacq'ue'red material may be mounted and then I varnished.

The new material has the advantage for wall coverings that it is insensitive to blows, tension 1 and pressure, because of its plasticity and elasticity. Therefore cracks in the wall are not transmitted through the covering and remain invisible. In this respect the material is different from all previously known rolled-up wall-paper.

It must be remarked that ordinary veneer has not been until yet used for wall coverings because of its brittleness and of the difficulty of applying it to the wall.

What we claim is: 1. The process of making a thin piece of wood .soft and permanently flexible which comprises subjecting it to the action of 'an alkali solution of such a strength and for such a time that the natural wood structure is swollen and loosened without being destroyed and without destruction of the characteristic wood grain thereof,

washing, and then saturating with a water-sol uble substance such as glycerol, likewise of such a strength and for such a time as to avoid destruction of the natural wood structure and characteristic grain thereof.

-2. The process of making a thin piece oi wood soft and permanently flexible which comprises subjecting it to the action of an alkali solution of such a strength and for-such a time that the natural wood structure is swollen and loosened without beingdestroyed and without destruction of the characteristic wood grain thereof,

washing, and then saturating with a water-soluble substance such as glycerol, monoacetin or a lactate, in combination with an emulsified waterinsoluble substance such as a hydrocarbon, fat, oil, or soap, likewise of such a strength and for such a time as to avoid destruction of the natural wood structure and characteristic grain thereof.

3. The process of making a thin piece of wood soft and permanently flexible which comprises subjecting it to the action of an alkali solution of such a strength and for such a time that the natural .wood structure is swollen and loosened without being destroyed and without destruction of the characteristic wood grain thereof, washing,

then saturating with a water-soluble substancesuch as glycerol, likewise of such a strength and for such a time as to av'oid destruction of the.

thereof, and submitting the product to pressure.

- 4. The process or making a thin piece of wood stance such as glycerol, likewise of such a. sort and permanently flexible which comprises strength and for such a, time as to avoid destrucsubjecting it to the action of an alkali solution tion of the natural woodstructure and characterof such a strength and for such a time that the istic grain thereof, and-impregnating the prodnatural wood structure is swollen and loosened uctwith a lacquer.

without being destroyed and without destruction I ofthe characteristic wood grain thereof, wash- REGINALD OLIVER HERZOG. mg, then saturating with a water-soluble sub.- ALFRED BURGENI.