BACKGROUND OF THE INVENTION
[0002]
Liquid absorbent products such as paper towels, tissue paper, feminine hygiene products, industrial wipers, food service wipers, napkins, medical pads, and other similar products are designed to include several important properties. For example, the products should generally have good bulk, a soft feel and should be highly absorbent. The products should also have strength even when wet and should resist tearing. Furthermore, many products should also have good stretch characteristics, should be abrasion resistant, and should not deteriorate in the environment in which they are used.
[0003]
One process that has proven to be very successful in producing soft, absorbent, single ply fibrous webs having a laminate like structure that are particularly well suited for use as wiping products is disclosed in U.S. Pat. No. 3,879,257 to Gentile, et al., which is incorporated by reference in its entirety.
[0004]
The fibrous webs disclosed in Gentile et al. are formed from an aqueous slurry of principally lignocellulosic fibers under conditions that reduce interfiber bonding. A bonding material or creping composition such as, for example, a latex elastomeric composition, is applied to a first surface of the web in a spaced-apart pattern. The bonding material provides strength to the web as well as abrasion resistance to the surface of the web.
[0005]
Once the bonding material is applied to the first side of the web, the web can be brought into contact with a creping surface. Specifically, the web will adhere to the creping surface according to the application pattern of the bonding material. The web is then creped from the creping surface with a doctor blade. Creping the web greatly disrupts the fibers within the web thereby increasing the softness, absorbency, and bulk of the web.
[0006]
In one embodiment disclosed in Gentile et al., both sides of the web are creped after the bonding material has been applied. Thus, the bonding material can be applied in a manner similar to that of the first side to the opposite side of the web to provide additional strength and abrasion resistance.
[0007]
Bonding materials used in creping fibrous webs typically include a crosslinkable polymer that contains functional groups, such as n-methylol acrylamide, that are crosslinked in the presence of an acid catalyst during the creping process. However, the crosslinking reaction often generates formaldehyde, such as by a condensation reaction, which is absorbed by the fibers of the web and remains resident in the resulting creped product.
[0008]
Increasingly, regulations and health concerns have mandated lower and lower formaldehyde levels in products. Formaldehyde absorb by the fibers (“free formaldehyde”) can be released to the surrounding environment at a pH of 7 or greater such as when the fibers are wetted. Additionally, the released formaldehyde can react with other compounds in or on the fibers to form undesirable and/or noxious odors. For example, when formaldehyde reacts with ammonia a methylamine compound having a distinctly fish-like odor can be produced.
[0009]
Some manufacturers of creping materials have attempted to reduce the level of formaldehyde generated during crosslinking by adjusting the degree of crosslinking and by utilizing various acid catalysts. Others have attempted to control formaldehyde emissions from creped materials by including high surface area pigments, such as diatomaceous earth, or malodor absorbers, such as certain organic acids. However, many of these treatments are sprayed or coated onto the surface of the creped product as a post-forming treatment thereby adding an additional production step.
[0010]
With the foregoing in mind, there is a need or desire for a bonding material or creping composition that produces a lower amount of free formaldehyde residue in a creped material. There is also a need or desire for a creped material that includes a lower level of free formaldehyde and may be produced efficiently and economically.
[0011]
Therefore, it is a feature and an advantage of the present invention to provide a creping composition that produces a reduced level of free formaldehyde residue in a creped material. It is a further feature and advantage to provide a creped material including the creping composition of the present invention having a lower level of free formaldehyde residue than a comparable creped material.
