Product containing high density skins

A method of forming a cellulosic fiber containing board having a relatively dense skin on at least one of its surfaces comprising:

• impregnating a consolidated cellulosic fiber containing mat, with urea in an amount in the range of 5-20% based on the dry weight of the mat material contacted with urea;
• and
• pressing said impregnated mat at a temperature of at least 525.degree. F., said skin formed during said hot-pressing on the surface of said mat impregnated with urea.

In a method of manufacturing a fiber-board, including the steps of hot-pressing a cellulosic fiber-containing mat to consolidated said mat into a unitary structure having a density in the range of 10-65 pounds per cubic foot, the improvement comprising impregnating at least one surface of said consolidated mat with urea in an amount of at least 5% based on the dry weight of the portion of the mat contacted with said urea and thereafter hot-pressing said impregnated, consolidated mat at a temperature of at least 525.degree. F. for a period of time sufficient to form a hard, dense skin on the surface of said mat, said skin formed during said hot-pressing on the surface of said mat contacted with urea.

A method of forming a hard, dense skin on the surface of a fiberboard comprising:

• contacting the surface fibers of a cellulosic fiber-containing mat with urea;
• and thereafter
• hot-pressing said mat after consolidation in a heated press at a temperature of at least 525.degree. F. to form a board having a skin on said surface of said mat, said skin being of different composition than the composition of the material on which the skin is formed, said skin formed during said hot-pressing on the surface of said mat contacted with urea.

A method of manufacturing a cellulosic fiber-containing board having a skin on at least one surface thereof comprising:

• depositing a first layer of fibers to form a base layer for supporting at least one surface skin thereon;
• depositing a second layer of fibers over said first layer of fibers, said second layer of fibers including urea in an amount of at least 5% based on the total weight of said second layer of fibers;
• consolidating said first and second layers in a heated press at a temperature less than 500.degree. F. and at a pressure less than 700 psi to form a consolidated mat and thereafter hot-pressing said consolidated, mat at a temperature in the range of 525.degree.-650.degree. F., and at a pressure not exceeding 300 psi to form at least one skin on said base layer, said skin formed during said hot-pressing on the surface of said mat including urea.

A method as defined in claim 21 further including depositing a third layer of fibers in contact with said base layer, prior to consolidation of said first and second layer to thereby sandwich said base layer between said second and third fibrous layers, said third layer of fibers including urea in an amount of at least five percent based on the total weight of said third layer of fibers;

• and consolidating said three layers prior to said skin forming hot-press step.

A fiberboard or particle board product comprising a base layer comprising cellulosic fibers and a binder, said base layer having a density in the range of 10-65 pounds/ft..sup.3 ;

• and an integral skin disposed on at least one face of said base layer, said skin having a density in the range of 40-55 pounds/ft.sup.3 and formed by including urea within the surface fibers of said fiberboard, in an amount of 5-20% based on the dry weight of fibers containing urea, consolidating said fiberboard to provide a base layer having a density in the range of 10-35 pounds/ft.sup.3, and thereafter heating said contacted surface fibers, under pressure, at a temperature of at least 525.degree. F., to form said skin during hot-pressing on the surface of said mat containing urea.

In a method of manufacturing a fiberboard, including the steps of consolidating a cellulosic fiber-containing mat into a mat, the improvement comprising impregnating at least one surface of said consolidated mat with urea in an amount of at least 5% based on the dry weight of the portion of the mat contacted with said urea, and thereafter hot-pressing said impregnated, consolidated mat at a temperature of at least 525.degree. F. for a period of time sufficient to form a hard, dense skin on the surface of said mat, said skin formed during said hot-pressing on the surface of said mat contacted with urea.