Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-11-04
2002-05-14
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S186000, C524S191000, C524S210000, C524S227000, C524S589000, C524S590000, C524S591000
Reexamination Certificate
active
06387994
ABSTRACT:
FIELD OF THE INVENTION
This invention provides a new class of solid solvent viscosity depressants for use in preparing blends with block copolymers such as polyether-polyurethane block copolymers, polyester-polyurethane block copolymers, or other block copolymers described below. The blends are useful as adhesives.
BACKGROUND OF THE INVENTION
Polymers of all types have proven to be very useful materials in modern society, and many different methods have been developed in order to shape them into useful forms. One of the simplest methods is thermal processing, where a polymer is heated to a temperature at which it flows, is then shaped into its final form by processing machinery, and then is allowed to cool and solidify. This method is widely used because it efficiently uses the polymer material, and generally does not produce large waste streams which must be properly disposed of. However, some materials are difficult to process thermally. The polymer may degrade undesirably at the processing temperature, and yet lowering the processing temperature is not always practical because the polymer viscosity becomes too high for proper processing.
Another method of processing polymers is to make solutions by blending a suitable liquid solvent with the polymer. The solution viscosity is often low enough that the processing can be done at room temperature, although processing of heated solutions is not uncommon. In any case, lower viscosities can be obtained at lower processing temperatures than for the pure polymer, which eliminates problems due to degradation at high processing temperatures. Solvent processing does have many drawbacks, however. The solutions are often made from solvents which are highly flammable and/or present health hazards via inhalation and skin contact. The solvents must be removed and properly disposed of, which is often an involved and expensive process, especially as governmental regulations concerning airborne emissions have become increasingly stringent. Solution processing is usually limited to forming the polymer into thin films.
It is important to reduce a polymer's melt viscosity in some instances, for example, where a polymer has such a high viscosity that it is difficult to extrude or mold. However, sometimes the viscosity cannot be lowered by increasing the temperature because of decomposition concerns, and the disadvantages of traditional liquid solvents make their use unacceptable.
A more recent method of processing polymers is with the aid of solid solvents. Solid solvents are additives which act as a solvent for a particular polymer above a certain temperature A polymer/additive solution forms in which the melt viscosity of the solution is lower than that of the polymer itself. Thus solid solvents are used where it is desired to lower the melt viscosity and/or processing temperature of the polymer. On the other hand, below that temperature, the solid solvent precipitates out of the polymer and becomes a filler. This eliminates the need for solvent removal that is associated with traditional liquid solvents. Solid solvents are generally low molecular weight crystalline compounds. In operation, a properly functioning solid solvent additive melts at or below the processing temperature, and is soluble such that it reduces the viscosity of the polymer/additive blend to a lower level than that of the base polymer. At use temperature of the final article, the solid solvent functions as a filler, not as a plasticizer. For example, if increased softness or tack are not desired in the final article, the use of a solid solvent avoids exacerbating these undesirable properties in comparison to the base polymer. Solid solvents are different from traditional liquid solvents or lubricants. A traditional liquid solvent adversely affects the mechanical properties of a polymer unless it is removed. A lubricant is not soluble in the base polymer and does not reduce viscosity at low additive levels.
Some classes of solid solvents suitable for homopolymers and random copolymers polymers are known. For example Chung U.S. Pat. No. 5,157,068 teaches that low molecular weight crystalline carboxylic acids and their derivatives act as solid solvents to improve the processibility of vinyl chloride polymers; and in U.S. Pat. No. 4,843,117, Chung teaches that dimethyl sulfone does the same for vinylidene chloride polymers. Buckley, U.S. Pat. No. 4,434,262 teaches an improved melt-processible blend of a polyolefin or polyester in which a solid solvent is present that is N, N′-bis(p-methoxybenzylidene)-alpha, alpha′-bi-p-toluidine; p-methoxycinnamic acid; N, N′-bis(4-octyloxybenzylidene)-p-phenylenediamine and lithium stearate. However, none of the solid solvents taught are suitable for block copolymers for one or more of the following reasons: Ineffective viscosity depression, excessive deterioration of physical properties, reactivity with the polymer, and excessive volatility at processing temperatures.
SUMMARY OF THE INVENTION
A new class of solid solvents has now been found, which properly function as solid solvents when blended into block copolymers. This new class of solid solvents helps overcome some of the dissadvantages traditionally associated with the thermal processing of block copolymers, and yet has little detrimental affect on physical properties at use temperatures. A particularly useful aspect is when the blend is used as an adhesive and the substrate to which the adhesive is to be applied has pores, cavities, or other surface irregularities. This is because with a lower melt viscosity during the application process, the adhesive can more easily flow into the confined spaces of the substrate material. Examples of processes which benefit from the adhesives made from the blends of this invention include lamination of fabrics and sealing of fabric seams.
It is a purpose of this invention to provide a new class of solid solvents for melt-processible block copolymers, such as polyurethanes, e.g. polyether-polyurethane block copolymers or polyester-polyurethane block copolymers, polyester-polyether block copolymers, polyamide-polyether block copolymers, and polyamide-polyester block copolymers.
It is another purpose to provide a new class of solid solvents for adhesives containing the previously mentioned block copolymers.
It is still another purpose to provide seam tapes containing solid solvents for sealing fabric seams.
It is still another purpose to provide protective fabrics with seams sealed with tape containing the new class of solid solvents in certain polymers. By protective fabric is meant a fabric that protects against the adverse influence of liquids, gases, viruses, or the like.
In one aspect, the compounds that have been found effective as solid solvents for block copolymers have a molecular weight less than 600, contain two functional groups selected from either amide or carbamate groups, and have at least two aromatic rings in the structure. Such solid solvents for block copolymers, hereafter referred to as block-copolymer solid solvents, include adipamides, bisacetamides, biscarbamates, and dibenzamides.
In another aspect, the blockcopolymer solid solvents can be represented by the formula:
R″-X-R′-X-R′″
wherein:
where R″ and R′″ can be the same or different and are selected from alkyl of 1-6 carbons or phenyl; each X is the same and is selected from divalent amide or divalent carbamate; R′ is alkylene of 1-6 carbons, methylene diphenylene or oxydiphenylene. And when R″ and R′″ are alkyl, R′ is oxydiphenylene or methylene diphenylene.
It is understood that the aromatic groups may contain common substituents such as alkyl, halo, or the like, so long as the desired properties of the block copolymer are not significantly reduced.
Block copolymers exhibit an unusual combination of toughness and flexibility which has been attributed to a distinct 2-phase morphology at use temperatures. The molecules of the block copolymer consist of 2 types of structures; a stif
Blake Holly
Gore Scott
Niland Patrick D.
W. L. Gore & Associates, Inc.
Wheatcraft Allan M.
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