US2343016A - Flexible wood product - Google Patents

Description

. Patented F ebo 29, ran

. errant HEXEIE W001i) PRODUCT William Karl llioughborough, Madison, Wis.; dedicated to the free use of the People in the territory or the United States No Drawing. Application January 7, 1942, Serial No. 425,867

1 Claim. (@i, IVA-09) (Granted under the act oi ldarch 3, 1883, as

. amended iipril 30, l

. This application is made under the act of March 3,1883, as amended by the act'of April 39, 3.928, and the invention herein described and claimed, if patented, may be manufactured and used by or for the Government of. the United States of America for governmental purposes without the payment to me of any royalty thereon.

I hereby dedicate the invention herein, de-

scribed to the free use 01 the People in, the territory or the United States to take effect on the granting of a patent-to me. I

My invention relates to processes for rendering dry wood flexible at all temperatures.

Another object of my invention relates to a secondary treatment, whereby the wood complex is converted from a product of no elasticity to one having a high degree of elasticity.

In my prior Patent No. 2,298,017, datedOctoher 6, 1942, there is taught'that when green southern swamp white oak is impregnated with a suitable amount of urea and then dried to a low moisture content, it becomes so soft and flexible that it may be very easily-bent, twisted or otherwise deformed when heated to atemperature of about 215 F. It is further disclosed that any form given the wood when hot is retained by the product when cooled to room temperatures. In other words, the urea comrbines with some or all of the elements of the natural wood to form a thermoplastic resin. A a

product that becomes plastic on heating is obviously undesirable for certain purposes. Hence, efiorts were made to develop a process for resinltying the plastic wood, thus converting the thermoplastic product into a thermosetting product. This change is brought about by treating the compressed urea treated wood with an aldehyde, preferably formaldehyde, either as an aqueous solution or as ages. This invention is disclosed in my prior Patent No; 2,313,953, dated March 16, 1943.

The present invention difiers'fromthe above in that the treated wood of any thickness or length, whether laminated or not, unlike the product disclosed in Patent No. 2,298,017 is exceedingly flexible, even when cold.

1 am also familiar with another process which renders wood permanently plastic by the application of a compression parallel to the grain load in excess of the elastic limit. My present invention differs from this process, in that the load is applied to the urea treated wood at right angles to the grain. Moreover, according to the present invention. the wood is not rendered per-- manently plastic., It can be given greater strength and stiffness by the secondary aldehyde treatment.

A specific method that may be employed in producing the product covered by this invention is as follows:

I may soak green sweetgum veneer for two days in an aqueous urea solution that is saturated at room temperature. It may then be dried to a weight which is in equilibrium with C. and. 40 percent relative humidity-which would ultimately dry normal Wood to a moisture content of 6 percent. The treated sheets, either separately or laminated, are placed in a female form or chase and subjected to a slight pressure while their temperature is raised to about 175 C. when a maximum pressure of substantially 500 pounds per square inch is applied at right angles to the grain. Before the pressure is finally re-. leased, the product is cooled to a temperature of about 60 C. These conditions of maximum pressure and temperature are maintained for a period which varies with the thickness and species of material being pressed. I have found that with thicknesses of about one-half inch, about 15 minutes at maximum temperature and pressure is sufficient to produce a panel which is surprisingly plastic at all temperatures, even when maintained at'a moisture content that is in equilibrium with normal room atmosphere.

The product treated as above can be curved, or otherwise deformed, and while being held to the desired shape, placed in a bath of commercial formaldehyde solution, or a saturated solution of dimethanal urea, or treated-in formaldehyde in the gaseous state, or treated in any aldehyde which, in combination with urea, forms a thermosetting resin.

In order to produce my product, via, a resinified sheet wood material, it is first necessary to remove any excess moisture, then heat the urea aldehyde product to a temperature of about Accordingly, it will be seen that I may produce (1) a wood product that is flexible at all temperatures, the flexibility having been brought about by a urea treatment and by restraining transverse and longitudinal flow when subjected to a suitable press schedule of temperature and pressure; (2) a process of making wood flexible at all temperatures by first soaking it in a urea solution, drying it, and finally placing it in a suitable female form or chase and compressing it to about half of its original thickness at elevated temperatures, and finally cooling under pressure; (3) a wood product or great strength and stillness produced by subjecting the flexible wood, as described in (l), to an aldehyde; and (4) a process tor'making the flexible woodprodnot, described in (1), into a product of great strength and stillness;

Having thus described mi invention, what I claim for Letters Patent is:

A process of making wood flexible at all temperatur'es, comprising the steps or first saturat- 10 in: the wood in an aqueous urea solution at room 1 temperature; thence drying to awelsht which is in equilibrium with substantially 60 C. and 40 percent relatirc humidity; thence subjecting the treated wood in the form of veneer or boards toatemperat'ure of substantially 175 C. and a pressure of substantially 500 pounds per square inch, thence cooling the product to a tempera-