Liquid purification or separation – Filter – Material
Reexamination Certificate
2000-05-19
2002-05-21
Kim, John (Department: 1723)
Liquid purification or separation
Filter
Material
C210S503000, C210S506000, C427S244000, C427S389900, C428S3550EN
Reexamination Certificate
active
06390305
ABSTRACT:
BACKGROUND OF THE INVENTION
Emulsion or solution polymers are used to saturate paper substrates to impart tensile and stiffness properties, humidity resistance, and durability under high temperature conditions. Filter paper production is one of the major application areas in which paper saturation is utilized. Currently, two different polymer systems are typically used in the industry to saturate paper, depending upon whether the end use for the paper is an air filter or an oil filter. For air filters, water-based emulsion polymers, such as ethylene-co-vinyl chloride emulsions together with an external crosslinker, such as a melamine-formaldehyde resin, are typically used as paper saturants. Using these water-based emulsion polymers, an air filter paper is produced which displays adequate air permeability, wet tensile strength, and wet stiffness. However, with advances in technologies, such as heavy duty machinery, farm equipment, heavy duty trucks, and advanced internal combustion engine designs, demands have increased for improvement of water resistance, solvent and oil resistance, and high temperature stiffness of filter papers. In addition, environmental concerns impose other constraints and limitations on what is considered an acceptable binder system. For example, systems with high formaldehyde levels resulting from the use of melamine-formaldehyde crosslinkers can be problematic.
For higher performance filter papers such as hot oil filters, fuel filters and vacuum filters, solvent-based phenolic resin binders have commonly been used. However, there are disadvantages in using solvent-based phenolics, such as environmental concerns related to solvent VOC's, problems with handling residual phenol, and environmental concerns regarding residual formaldehyde. Due, in part, to the disadvantages associated with solvent-based resin binders, there is a desire in the industry to switch to all water-based binder systems which have comparable performance to the phenolic resins for high performance filter papers.
Some currently known water-based binder systems for filters are described below:
U.S. Pat. No. 4,623,462 (Urig et al., 1986) discloses oil filters containing water-based latex binders. A filter substrate is impregnated with a water-based binder comprising a latex containing at least 20% polymerized vinyl chloride. The latex is a copolymer of vinyl chloride, 30 to 60% lower alkyl acrylate, and up to 5% one or more comonomers selected from acrylic acid and N-methylol acrylamide, based on the weight of monomers used to make the latex; said binder also containing 5 to 20 parts of a crosslinking resin per 100 weight parts of latex solids and 5 to 20% catalyst for the crosslinking resin based on the weight of the crosslinking resin.
U.S. Pat. No. 4,999,239 (lacoviello et al., 1991) discloses a binder composition, for application onto non bonded filter paper. The binder composition is an aqueous emulsion containing an ethylene-vinyl chloride copolymer and tetramethylol glycoluril and are prepared by incorporating 4 to 10 wt % tetramethylol glycoluril, based on the total weight of the emulsion copolymer, into an aqueous dispersion of a copolymer consisting essentially of 65 to 90 wt % vinyl chloride, 5 to 35 wt % ethylene and optionally, up to 10 wt % of a hydroxyalkyl- or carboxylic acid-containing functional comonomer. The polymerization is conducted in the presence of a poly(vinyl alcohol) stabilizing system. Filter paper, formed by impregnating paper or other suitable substrate with the copolymer emulsion, is reported to show enhanced resistance to hot oil.
U.S. Pat. No. 5,244,695 (Davidovich et al., 1993) discloses a method for making a nonwoven filter in which a nonwoven filter substrate is impregnated with a curable binder composition, consisting essentially of 10 to 100 wt % a poly(vinyl alcohol) which is at least 98 mol % hydrolyzed and has a DPn of 100 to 2300; and 0 to 90 wt % of an aqueous polymer emulsion. The aqueous polymer emulsion is an ethylene-vinyl chloride copolymer emulsion or a vinyl acetate/N-methylolacrylamide copolymer emulsion, or both.
U.S. Pat. No. 5,354,803 (Dragner et al., 1994) discloses a poly(vinyl alcohol) graft copolymer binder emulsion for nonwoven products. The binder emulsion comprises 12 to 35% of a fully hydrolyzed low or ultra low molecular weight poly(vinyl alcohol) (at least 75% of the poly(vinyl alcohol) is at least 98 mol % hydrolyzed) and 65 to 88% of a vinyl and/or acrylic monomer which is graft copolymerized with the poly(vinyl alcohol). Examples of suitable vinyl and acrylic monomers include C1 to C8 acrylate and methacrylate esters, vinyl acetate, styrene, acrylic acid, and methacrylic acid.
BRIEF SUMMARY OF THE INVENTION
This invention is directed to high performance filters which are formed from a substrate or basestock, such as a nonwoven or a cellulosic material, impregnated with an aqueous based poly(vinyl alcohol) graft emulsion copolymer as binder.
The aqueous based poly(vinyl alcohol) graft emulsion copolymers are prepared by graft polymerizing poly(vinyl alcohol) with one or more ethylenically unsaturated monomer, and optionally, a crosslinking monomer, in an aqueous medium, in which 30 to 100% of the total poly(vinyl alcohol) is 70 to 97 mol % hydrolyzed.
The aqueous based graft emulsion copolymer of this invention can be combined with a crosslinking agent and/or catalyst and applied to a filter basestock, such as filter paper. The treated basestock can then dried at an elevated temperature to produce a filter media which is suitable for a variety of high performance applications, such as air filters, hot oil filters, and vacuum filters.
There are several advantages in using the above described poly(vinyl alcohol) graft emulsion copolymers as binders to produce high performance filters. For example:
no solvent VOC's or residual formaldehyde are released into the environment during the production of the aqueous graft emulsion copolymer;
only a single curing cycle is required after the graft emulsion copolymer is applied to the filter basestock;
the treated basestock exhibits an excellent balance of stiffness, tensile, and air permeability; and
the treated basestock can be used in a wide range of filter grades, especially high performance filters, such as air, hot oil, fuel, and vacuum filters.
DETAILED DESCRIPTION OF THE INVENTION
The aqueous grafted copolymer emulsions of this invention can be prepared by free radical initiated polymerization of one or more ethylenically unsaturated monomer in an aqueous solution of poly(vinyl alcohol).
Poly(vinyl alcohol) is derived from vinyl acetate polymers. The vinyl acetate polymers are formed by polymerizing vinyl acetate as a homopolymer or in conjunction with other monomers to form copolymers and are then hydrolyzed to form poly(vinyl alcohol) or vinyl alcohol copolymers. The mol percent of vinyl alcohol in the poly(vinyl alcohol) or vinyl alcohol copolymers should be sufficient to enable free radical graft polymerization in an aqueous solution; i.e., render the polymer at least partially soluble in an aqueous medium.
The poly(vinyl alcohol) used in this invention, generally, has a weight average molecular weight (M
W
) ranging from about 5,000 to 150,000, preferably 10,000 to 120,000. Alternatively, the poly(vinyl alcohol) can have a degree of polymerization (Dp) of from 100 to 3,000, preferably 100 to 2000. Poly(vinyl alcohol) is made commercially by the hydrolysis of poly(vinyl acetate) and typically has a hydrolysis level ranging from about 85 to greater than 99 mol %. For this invention, the level of hydrolysis can range from 70 to greater than 99 mol %, preferably 85 to 99 mol %, provided that at least 30% of the total poly(vinyl alcohol) used in the grafting reaction is 70 to 97 mol % hydrolyzed, preferably 85 to 95 mol % hydrolyzed. Mixed poly(vinyl alcohol) grades, from combinations of poly(vinyl alcohol) polymers which vary in molecular weight and hydrolysis level, can be employed in the present invention.
Suitable monomers which can be employed for graft copo
Davidowich George
Jones Ronald Bernal
Lenney William Edward
Rabasco John Joseph
Air Products Polymers, L.P.
Bongiorno Mary E.
Kim John
LandOfFree
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