Paper making and fiber liberation – Apparatus – Web creping or crinkling type
Reexamination Certificate
2001-05-17
2003-05-20
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Apparatus
Web creping or crinkling type
C015S256510, C118S261000, C118S413000, C428S102000, C428S113000, C428S208000
Reexamination Certificate
active
06565712
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite composition to be used in a doctor blade construction. In particular, this invention relates to a composite composition used in a doctor blade construction wherein the composition has one or more inner layers comprising an engineering thermoplastic resin filled with heat-resistant, non-glass, long-strand fibers (e.g., carbon fibers or aramid fibers); one or more intermediate layers of carbon; and one or more outer layers of surface sheeting.
2. Brief Description of Art
Doctor blades contact the surface of rotating rolls of papermaking machines for various purposes, such as roll cleaning and sheet shedding. Conventional doctor blades have been made of a wide variety of materials including metals and various composites.
Composites have been used for making doctor blades in paper-making plants for many years. Generally, these composites have consisted of two parts, a substrate and a bonding agent for laminating together the layers of substrate. The commonly employed substrate materials have been paper, cotton fabric, glass fabric, finely woven or non-woven carbon fiber, unidirectional carbon layer or tape and synthetic fabrics. The latter includes polyesters, nylon, and acrylics. The commonly used bonding agents have generally been thermoset plastics such as phenolics or epoxies.
There are several particular challenges in selecting a suitable combination of substrates and bonding agents. First, bonding agents having better heat resistance are more likely to give poor inter-laminar bond strength. Secondly, bonding agents having both good water resistance and good chemical resistance generally have poor inter-laminar bond strength. Third, thinner doctor blade construction is preferred over thicker materials, but stiffer substrates most suitable for thinner constructions (e.g. fiberglass) may be too abrasive and thus are more apt to damage the rolls upon which the doctor blade operates. Accordingly, the selection of a proper composite for a doctor blade has been difficult and is, in many cases, application-specific.
U.S. Pat. No. 4,549,933 that issued to Judd et al. on Oct. 29, 1985 describes a composite doctor blade having a plurality of juxtaposed fibrous layers that are encapsulated in an epoxy resin. These fibrous layers include a fibrous core surrounded by a intermediate unidirectional graphite layer and then outer fibrous layers. A critical feature of the invention covered by this patent is that the intermediate unidirectional graphite layers must be oriented in the machine direction. This patent is incorporated herein by reference in its entirety.
In recent years, some engineering thermoplastic resins have been used as the bonding agent in doctor blades. These have good inter-laminar bond with good heat resistance. They also lend themselves to supporting long strand substrate fibers better than common thermoplastics such as polyethylene and polypropylene.
Some substrates that are useful with phenolic or epoxy-type bonding agents are not always useful with engineering thermoplastic resins because of the relative high processing temperatures needed to convert these latter resins into composites. For example, substrates such as cotton, paper, and some synthetic fibers (e.g. polyesters) may burn or melt when processed with certain engineering thermoplastic resins to make composites.
The substrates previously used with the engineering thermoplastic resins have been either glass fibers and/or carbon (e.g. woven fibers or unidirectional layers). Glass fiber substrates are not always favored because they are subject to water absorption and can be very abrasive to some materials. Accordingly, doctor blades containing glass fibers have been limited to use on the dry end of paper-making machines and can not be used on the wet end of the paper-making machines where softer rolls may be damaged.
Composites using only unidirectional carbon layers as the substrate, while being very stiff and wear resistant, are sometimes very difficult to conform to the shape of the roll. Accordingly, they may take an unreasonably long time to conform to the roll upon which they operate. During that break-in time, the doctor blade and the paper-making machine do not operate as efficiently as desired.
Most recently, unidirectional carbon layers, woven polyester fabric and an epoxy bonding resin have been combined to make a thin doctor blade for the use on the wet end of the machine. While this combination is stiff yet non-abrasive, it has a limited use because of its susceptibility to water, heat and chemical attack.
BRIEF SUMMARY OF THE INVENTION
Therefore, one aspect of the present invention is directed to a composite composition to be used in a doctor blade construction, said composite composition comprising:
(a) one or more central layers comprising an engineering thermoplastic resin filled with heat-resistant, non-glass, long strand fibers;
(b) one or more intermediate layers positioned over the one or more central layers, each said intermediate layer comprising at least one carbon layer; and
(c) one or more surface sheets positioned over the one or more intermediate layers.
Another aspect of the present invention is directed to an elongated doctor blade construction having a side edge structured for application to a roll surface in a paper making machine, said blade comprising a composite as defined above.
The composite composition of the present invention has several important advantages over the composite compositions previously used for doctor blades. This present composite will more quickly conform to the shape of the rolls in a paper-making operation than a composite containing all unidirectional carbon substrate, yet will wear for a desirably long time so that replacements are not frequently needed. This present composite also avoids the use of abrasive fiberglass that, when used in doctor blades, may cause wear on the rolls. Furthermore, the present composite has more water resistance than composite laminates that employ fiberglass and has more chemical resistance than composites containing epoxy resins. The composite compositions of the present invention may also be made into doctor blade constructions that have reasonable overall thickness (e.g. from about 0.008 to 0.2 inches in thickness) so that undesirable high torques and excess power losses are not needed to operate these blade constructions. Also, the doctoring edge of these composite doctor blades of the present invention may be sufficiently stiff in the machine direction so they do not easily deflect outwardly during operation, thus preventing the material that is being doctored to work its way between the blade and the roll surface being doctored. Furthermore, the heat resistant nature of the materials in the present composite blade construction will not degrade or lose stiffness or develop blisters when operating at the elevated temperatures (e.g. about 70-100° C.) normally associated with the wet end of a paper-making operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The term “composite” as used in the present specification and claims is defined as a material created by the synthetic assembly of two or more materials including a selected filler or reinforcing elements (also referred to as a “substrate”) and compatible matrix binder (also referred to as a “bonding agent”) to obtain specific characteristics and properties useful in a doctor blade construction. It is preferable to use an advanced composite composition for the present invention that contains both an engineering thermoplastic resin bonding agent matrix and reinforcement elements both havingunusually high performance properties.
The term “laminate” as used in the present specification and claims is defined as a preferred composite construction made by bonding multiple flat layers or sheets of substrate material with a bonding agent, usually in combination with pressure and heat, into composite composition.
The term “engineering thermoplastic resin
Griffin Steven P.
Halpern M.
Lingol Corporation
Wiggin & Dana LLP
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