The prior art has recognized the potential of peat moss material for use as an absorbent medium in structures for absorbing body exudate. Peat moss material has highly desirable fluid absorption properties such as a remarkable absorption capacity and the ability of "drying" adjacent materials by continuing to pull or wick fluid away from them over a long time period such that virtually all the fluid is collected in the peat moss core. These attributes allow the material to provide highly efficient absorbent components which can be made relatively thin for better fit, comfort and discretion, while being sufficiently absorbent to prevent overflow leakage and garment staining.
The following United States Patents document the use of peat moss material for manufacturing absorbent components for disposable absorbent products:
______________________________________ U.S. Pat. No. INVENTOR DATE ISSUED ______________________________________ 4,170,515 Lalancette et al. October 9, 1979 4,215,692 Levesque August 5, 1980 4,226,237 Levesque October 7, 1980 4,305,393 Nguyen December 15, 1981 4,473,440 Ovans September 25, 1984 4,507,122 Levesque March 26, 1985 4,618,496 Brasseur October 21, 1986 4,676,871 Cadieux et al. June 30, 1987 4,992,324 Dube February 12, 1991 5,053,029 Yang October 1, 1991 ______________________________________
The subject matter of these references is incorporated herein by reference.
Peat moss material can be formed in a highly cohesive board by using any one of the methods disclosed in the above-identified prior art. In a board form, the peat moss material is convenient to handle and it can be directly processed in high speed automatic equipment for assembling disposable absorbent products.
More particularly, the method for producing the peat moss board consists of screening raw peat moss material in particulate form to retain only the particles which are the most absorbent. The screened fraction is then formed into a slurry which is sheeted on a Fourdrinier wire and dewatered by the application of vacuum. The thus formed board is dried and calendered to increase its density to the desired level. In order to tenderize, soften and improve the flexibility of the calendered peat moss board, it may be subjected to mechanical working such as perf-embossing and micro-corrugating as described in the U.S. Pat. Nos. 4,559,050 and 4,596,567 issed to Iskra on Dec. 17, 1985 and Jun. 24, 1986. The disclosure of these patents is incorporated herein by reference.
The prior art has recognized the importance of controlling certain variables during the manufacturing process of the board in order to maintain the absorbency of the final product within acceptable limits. In this regard, the U.S. Pat. No. 4,473,440 Ovans, issued on Sep. 25, 1984 is of interest. This reference teaches to regulate the water content of the absorbent board immediately before the calendering operation with relation to the weight percent of the peat moss material in the board.
It is also known to those skilled in the art that the density of the peat moss board is an important parameter which markedly influences its absorption properties and its comfort potential. In currently practised methods for manufacturing peat moss boards, the density control is achieved by trial and error which essentially consists of changing certain variables that are known to influence the density of the board, until the desired density of the final product is achieved.
Presently, the limited knowledge and understanding of the various factors determining the density of the peat moss board do not allow a strict and rigorous process control. As a result, undesirable fluctuations in the properties of the final product are difficult to avoid.