Carbonyl compounds (e.g. acetone and acetaldehyde) are often present as impurities in oxygenated organic liquids such as acetic acid made by the carbonylation of methanol or in phenol produced by the oxidation of cumene. These impurities can render petrochemical products unsuitable for long-term storage or otherwise adversely affect downstream processing operations. It has now been found that detrimental carbonyl impurities can be easily removed from oxygenated organic liquids by contact with resins having amine functional groups.

The present invention relates to a novel method for treating an oxygenated organic liquid stream contaminated with a carbonyl impurity such as acetaldehye or acetone. Contacting the organic liquid with a resin having an amine functional group effectively removes the undesired carbonyl compounds.
Adsorptive techniques to remove carbonyl compound impurities have been applied for different reasons to a variety of industrial product streams. For example, Japanese patent 2737290 discloses the use of mineral acid salts of hydrazine-group containing ion exchange resins for the removal of aldehydes from waste water. The adsorptive separation reduces the odor of contaminated water. Canadian patent application 2052435describes the use of a solid nonionic polystyrene adsorbent to remove unsaturated aldehydes, thereby improving beverage (e.g. beer) stability and taste. U.S. Pat. No. 5,132,456 sets forth a process for separating carboxylic acids from aqueous feedstocks by contact with an acid-sorbing phase that can include a weakly to moderately basic anion exchange resin.
The adsorption of carbonyl compounds from hydrocarbon streams, particularly olefinic liquids, has proven beneficial in terms of facilitating downstream processing operations. In German patent 3512352, for example, the adsorptive removal of carbonyl sulfide from a propene stream is carried out to improve its quality as a feedstock for subsequent polymerization in the presence of a Ziegler catalyst. The adsorbent material in this case is an anion exchange resin having an amine function. Soviet Union patent application 695996 discloses several types of resins effective for the removal of carbonyl compounds from isobutylene. The purification of this feed is taught to improve the quality of the butyl rubber end product, resulting from the copolymerization of the purified isobutylene with isoprene.
In addition to carbonyl compound removal from liquid aqueous and hydrocarbon streams, the prior art has also addressed the need to free oxygenated organic liquids of these reactive impurities. Of particular concern is the purification of carboxylic acids, (which are themselves carbonyl compounds) containing trace amounts of carbonyl impurities such as aldehydes and ketones. It is well documented that these impurities invariably contaminate commercial acetic acid products resulting from the catalytic carbonylation of methanol with carbon monoxide, a process that serves as the basis for virtually all new acetic acid capacity. Acetic acid is industrially significant, mainly due to its use in the production of purified terephthalic acid and vinyl acetate monomer.
Methods for manufacturing acetic acid by methanol carbonylation that have proven commercially successful are described in U.S. Pat. No. 3,769,329, and more recently in U.S. Pat. No. 5,001,259. The ""259 patent discloses a method for maintaining high catalyst activity and stability in the methanol carbonylation environment by using a specified amount of iodide ions above that which is normally present as methyl iodide or other organic iodide promoter. A distinguishing characteristic of this process, compared to that described in the earlier ""329 patent, is the ability to achieve competitive reaction rates and prevent catalyst precipitation at reactor water levels of only 4 wt-% or less. In U.S. Pat. No. 5,344,755, another type of low water process is described, where a supported rhodium (i.e. heterogeneous) catalyst is used in place of the homogeneous catalysts set forth in the former ""329 and ""259 references.
It is recognized in the art that acetic acid produced by methanol carbonylation, and particularly using the low water processes of the aforementioned ""259 and ""755 patents, contains a considerable amount of byproduct impurities which can be detected based on their reducing action on permanganate solution. Furthermore, these impurities are not easily separable using the conventional distillation schemes downstream of the carbonylation reactor section designed to purify the product acetic acid from catalyst, methyl iodide promoter, water, and methyl acetate. The presence of such impurities is highly undesirable because they adversely affect the product permanganate time, an important commercial test (STM.170) of the acetic acid quality. Even small amounts of reducing impurities can degrade the stability, usefulness, and overall salability of the acetic acid product. Reducing impurities that have been found to significantly impact permanganate time include, but are not limited to, saturated and unsaturated aldehydes, namely acetaldehyde, butyraldehyde, crotonaldehyde, 2-ethyl crotonaldehyde, 2-methyl 2-pentanal, and 2-ethyl butyraldehyde. Additionally, other undesired carbonyl species such as the ketones acetone and methyl ethyl ketone normally exist to some extent in the final acetic acid. Although such carbonyl compounds may have little or no effect on the permanganate time, their removal is desired in order to improve the overall purity of the product.
The importance of purifying commercial acetic acid streams of various carbonyl contaminants (and especially reducing impurities) is apparent from the prior art references dealing with this problem. For example, U.S. Pat. No. 5,155,265 proposes reacting the carbonyl impurities with ozone to form a reactive oxygenated species or complex that can thereafter be more easily separated. This removal is carried out by passing the ozone-treated acetic acid through a carbonaceous material. Additionally, the effluent from this removal step is optionally contacted with a macroreticulated strong acid cation exchange resin which is stable in the acetic acid and has at least one percent of its active sites converted to the silver or mercury ion-exchange form.
U.S. Pat. No. 5,371,286, herein incorporated by reference, identifies particular intermediate streams in commercial acetic acid processing that contain relatively high concentrations of carbonyl impurities. Specifically, the overhead liquid stream from a commonly employed fractionator to separate primarily methyl iodide and acetic acid (referred to as the xe2x80x9csplitterxe2x80x9d column) tends to accumulate substantial quantities of carbonyl compounds, particularly acetaldehyde. If sufficient water is present, this stream will phase separate, with the carbonyl impurities partitioning preferentially into a heavy phase. In either case, the splitter column overhead or some portion thereof can be routed to another column for further processing by distillation and phase separation
European patent 0487284 B1 proposes an alternate treatment of the splitter column overhead stream, which, as mentioned previously, has a significant content of carbonyl compounds compared to other intermediate process streams. Specifically, the splitter column overhead can be contacted with a solution of a compound that reacts with the carbonyls to facilitate subsequent separation by distillation. The reactive compound in this case is an amino compound such hydroxylamine in aqueous solution. The reaction of hydroxylamine and the carbonyl impurities in an oximation reactor produces oximes. The oximes in the reactor effluent are first phase separated in an aqueous phase and then distilled for removal of the oximation products.
In U.S. Pat. No. 5,625,095, the benefits associated with maintaining an acetaldehyde concentration in the reactor of 400 ppm or less are disclosed, particularly in terms of reducing the amounts of carbonyl impurities and organic iodides in the acetic acid product. Process conditions to reduce the acetaldehyde concentration are described, which may be used alone or in combination with specific extraction and distillation procedures. U.S. Pat. No. 5,783,731 discloses the treatment of the vent gas stream of the splitter column overhead stream to remove relatively high levels of acetaldehyde contained therein. The treatment involves condensing the vent gas stream and further contacting it with an aqueous amino compound to allow the separation procedure as outlined in the aforementioned European patent 0487284 B 1.
In addition to the manufacture of acetic acid, the incorporation of carbonyl impurities is problematic in commercial phenol production as well. Practically all phenol is currently manufactured via the oxidation of cumene to cumene hydroperoxide, followed by the decomposition of cumene hydroperoxide to phenol and acetone. Modem production requires the attainment of very high quality specifications to render the product phenol suitable as a precursor for bisphenol A, expoxy resins, and other downstream products. While previous specifications allowed as much as 100 ppm of carbonyl compounds, these limits are progressively being reduced to 10 ppm or less. The adsorption of carbonyl impurities as a means of achieving these low tolerances provides a favorable alternative to current separations involving distillation.
Overall, the prior art recognizes that adsorptive separation using resins may be applied to the removal of carbonyl impurities from aqueous and hydrocarbon streams. With respect to oxygenated organic liquids such as carboxylic acids and phenols, however, the prior art has unfortunately not offered such a simple and effective means of removing carbonyl impurities. While the prior art distillation methods outlined above can provide a reduction in the amount of detrimental carbonyl impurities, they unfortunately require significant resources in terms of energy, equipment, and manpower. The solutions offered thus far for the removal of carbonyl impurities from acetic acid, for example, involve complex and expensive schemes requiring fractionation.
In contrast, the adsorptive method of the present invention, which utilizes a resin having an amine functional group, is a simple solution to the recognized problem of carbonyl contamination in oxygenated organic liquids. The utility of a resin having capacity selective for the adsorption of specific types of carbonyl impurities (e.g. acetaldehyde) from a liquid that itself contains predominantly carbonyl compounds (e.g. acetic acid) or other oxygenates (e.g. phenol) is indeed unexpected. Furthermore, a simple regeneration procedure can restore the resin activity after at least a portion of its functional groups have been used for carbonyl impurity removal.
In one embodiment the present invention is a process for treating an oxygenated organic liquid containing a carbonyl impurity, the process comprising contacting the liquid with an adsorbent comprising a resin having an amine functional group at adsorption conditions and adsorbing the carbonyl impurity on the adsorbent to yield a treated liquid stream.
In another embodiment, the invention is a process as described above where the adsorbent has substantially reached its adsorption capacity, at which point the adsorbent is regenerated by contacting it with a basic liquid at regeneration conditions.
In a further embodiment, the invention is a process for producing purified acetic acid, the process comprising reacting methanol and carbon monoxide in a carbonylation zone to produce a carbonylated product; flash vaporizing the carbonylated product into a heavy-boiling recycle stream and a crude acetic acid product; recycling the heavy-boiling recycle stream to the carbonylation zone; separating the crude acetic acid product into intermediate acetic acid streams and a final acetic acid product; and contacting at least one of the final acetic acid product and the intermediate acetic acid streams with an adsorbent comprising a resin having an amine functional group to yield a treated liquid stream.
It is also within the scope of the invention to combine the above process with suitable pre- and post-treatment steps known in the art to further purify either the final acetic acid product, intermediate acetic acid streams, or the treated liquid stream. The process may also be integrated with downstream operations such as the production of vinyl acetate monomer (VAM) from acetic acid or the manufacture of purified terephthalic acid (PTA) using an acetic acid solvent.
The feed stream for the process of the present invention includes broadly any oxygenated organic liquid containing a carbonyl impurity. Of commercial significance and particular applicability to the present invention are streams comprising predominantly carboxylic acids (e.g. acetic acid), phenols (e.g. phenol or bisphenol A), alcohols (e.g. methanol), anhydrides (e.g. acetic anhydride), and esters (e.g. methyl acetate). Typically, such streams are produced in industrial processes where the final product quality is of considerable importance, due to the impact of even trace impurities on the product stability and suitability for use in further processing operations. Of utmost concern to the present invention are oxygenated organic liquids resulting from either 1) the catalytic carbonylation of alcohols to produce carboxylic acids (e.g. acetic acid) or 2) the oxidation of aromatics to produce phenols (e.g. phenol).
In the particular case of modern methanol carbonylation technology to produce acetic acid, various commercial processes have been""developed and are described in detail in U.S. Pat. No. 3,769,329, U.S. Pat. No. 5,001,259, and other references. In general, the production process involves reacting methanol and carbon monoxide in a carbonylation zone (i.e. reactor), which is typically performed in the presence of catalyst having a metal function (e.g. rhodium or iridium) that is active for carbonylation. The resulting carbonylated reaction product is normally a mixture comprising acetic acid, methyl acetate, water, and methyl iodide. If a homogeneous (i.e. liquid phase) catalyst is employed, a substantial amount thereof will also be present in the carbonylation product.
The carbonylation product is flash vaporized to effect a separation of a crude acetic acid product in the vapor phase and a heavy-boiling recycle stream, often containing carbonylation catalyst, which is recycled back to the carbonylation zone. The crude acetic acid is then further separated by means comprising distillation, phase separation, extraction, and potentially other operations to provide a number of intermediate product streams and a final acetic acid product. Intermediate product streams, such as the aforementioned splitter column overhead stream, vary in type and composition depending on the specific methanol carbonylation process. In general, those streams having the highest concentrations of undesired carbonyl impurities are most suitable for the treatment process of the present invention. Otherwise, it is often most economical, for reasons explained below, to simply treat the final acetic acid product.
Regarding the final acetic acid product, varying levels of impurities are also present in this stream, depending on the specific methanol carbonylation process employed. Differences among the various industrial acetic acid production processes relate to reaction mixture compositions, separation schemes, and others that ultimately affect the final product composition. The acetic acid produced will normally contain a broad range of carbonyl impurities, that, as outlined in U.S. Pat. No. 5,783,731, include compounds containing saturated or unsaturated aldehyde or ketone functional groups. Specific types of carbonyl impurities known to contaminate commercially produced acetic acid, especially that made according to the low water processes described in U.S. Pat. No. 5,001,259 and U.S. Pat. No. 5,344,755, include, but are not limited to, acetaldehyde, butyraldehyde, crotonaldehyde, 2-ethyl crotonaldehyde, and 2-ethyl butyraldehyde. Because of their reducing ability, these carbonyl impurities, even if present in trace quantities in the acetic acid product, have an adverse affect on the product permanganate time test result, an important commercial measure of product quality. Acetic acid that is deficient with respect to permanganate time can present problems in downstream processing operations or may exhibit instability over periods of long-term storage.
To address commercial phenol manufacturing processes, many varieties of carbonyl impurities may appear in the final phenol product. The co-product acetone, for example, is a low-boiling carbonyl compound that is easily removed by distillation. Other carbonyls, however, are difficult or practically impossible to fractionate from the phenol product. These include, but are not limited to, hydroxyacetone, mesityl oxide, isophorone, and methyl benzofurans. Of these, hydroxyacetone is perhaps the most difficult to separate using conventional means. Currently, various methods exist for the removal of carbonyl impurities for the purification of phenol, but all of these techniques are highly energy intensive. A common procedure, for example, requires a crude phenol stream (after separation of acetone, cumene, alpha-methylstyrene, and high-boiling components) to be combined with steam and contacted in a phenol treating reactor with a mildly acidic catalyst such as silica-alumina or a zeolite. Under proper conditions, it is known that mesityl oxide can be hydrolyzed to acetone and that hydroxyacetone and phenol can be condensed to 2-methyl benzofuran. The reactor effluent is passed to a large fractionation tower where water is typically used as an extractive distillation agent. Purified phenol and high boiling components are recovered as a bottoms product while water and phenol at essentially azeotropic conditions are separated overhead. Due to the extractive distillation effect of water, 2-methyl benzofuran is also recovered with the low-boiling fraction and can be phase separated as an oily layer from the overhead receiver liquid. The bottoms phenol product from the extractive distillation is then routed to a rerun column where the final phenol product stream is removed as a low-boiling fraction. The high-boiling fraction, or bottoms of this rerun column, is typically recycled to the so-called xe2x80x9ctarxe2x80x9d or heavies column, which normally precedes the separation scheme described herein. The extractive distillation method, while effective for purifying phenol to 100 ppm by weight or less of carbonyl impurities, requires a large fractionator and substantial energy to boil the added extracting agent (e.g. water).
Other methods proposed for the removal of carbonyl impurities include the use of amine complexing agents such as hexamethylene diamine. Problems associated with this approach include the appearance of high-boiling amine-carbonyl complexes in the rerun column bottoms. If this stream is recycled to the aforementioned xe2x80x9ctarxe2x80x9d column, high reboiler temperatures will decompose these complexes, resulting in the release of carbonyl compounds back into the phenol product. If not recycled, the rerun column bottoms stream will represent a loss of not only the extracting agent, but also a significant proportion of the phenol product.
In contrast, the adsorptive method of the present invention provides a means to directly remove carbonyl impurities from a crude phenol product stream that would otherwise be directed to the phenol treating reaction and extractive distillation operations described above. In essence, the adsorptive separation eliminates these steps, along with the associated equipment and energy expenses, from the standard phenol purification flow scheme. Therefore, only conventional stripping (without extraction) and rerun fractionation towers are required for low- and high-boiling component removal, since the intermediate-boiling carbonyl impurities are now effectively adsorbed. Overall, the amine-substituted adsorbent effective for carbonyl impurity removal can be incorporated in place of the phenol treating reactor to treat the crude phenol stream. The extractive distillation column normally used is then converted to a simple stripping operation in this scenario. While this simplified flow scheme is suitable for new phenol production processes, existing commercial units might not be easily modified. For this reason, a practical alternative would be using the adsorbent of the present invention to treat the product (i.e. purified) phenol stream exiting in the rerun column overhead. Since this stream normally contains on the order of 100 ppm by weight of carbonyl impurities, the present invention can provide a means to realize more stringent targets in terms of carbonyl contamination of the final product. In a preferred embodiment, the adsorption process will reduce the level of carbonyl impurities in the treated liquid exiting the adsorbent bed to less than about 10 ppm.
In considering other types of oxygenated organic liquids that may be treated using the process of the present invention, final product streams of, for example, acetic acid or acetic anhydride production processes, where the product contains carbonyl impurities, are certainly applicable. Otherwise, it may be more economical to treat any of a multitude of intermediate process streams having an increased concentration of detrimental carbonyl compounds, compared to the final product. It should also be recognized that intermediate process streams may be treated to remove specific carbonyl compounds that are not themselves found to any significant degree in the final product, but are precursors to carbonyl impurities ultimately present in this product. For example, acetaldehyde is a precursor to higher molecular weight carbonyl impurities such as crotonaldehyde or higher aldol condensation products in the methanol carbonylation process environment.
In general, the term xe2x80x9cintermediate acetic acid streamxe2x80x9d includes all the process streams generated in reaction, distillation, phase separation, and other operations associated with the overall carbonylation of methanol to produce purified acetic acid. As mentioned, two industrially significant variations of these processes are disclosed in U.S. Pat. No. 3,769,329 and U.S. Pat. No. 5001259. Intermediate acetic acid streams in methanol carbonylation processes that are most applicable for the treatment process of the present invention are those having the highest concentrations of carbonyl impurities and thereby offering economically advantageous methods of treatment. Such streams are most often associated with the commonly used acetic acid-methyl iodide splitter column that effects a primary separation of the product. Specifically, as disclosed in the aforementioned U.S. Pat. No. 5371286 and U.S. Pat. No. 5,783,731, the splitter overhead receiver liquid and vent gas streams are known to contain relatively high concentrations (up to about 2 wt-%) of acetaldehyde. With respect to the overhead liquid, depending on the amount of water present, phase separation may lead to a further concentration of carbonyl impurities into a heavy, methyl iodide-rich stream particularly suitable for the adsorption process of the present invention.
Of course, treatment of the final product acetic acid stream is also an effective mode of carrying out the invention. Because the product stream is generally at or near the conditions of temperature and pressure most suitable for the adsorption of carbonyl impurities, there are normally no additional costs associated with heating, cooling, or pumping as might be incurred in the treatment of other process streams. A further consideration is that, depending on the various end uses of the acetic acid product, only a certain portion thereof may require treatment to remove carbonyl impurities. In this case, the product acetic acid stream, with all other factors being equal, is more likely to be the preferred feed stream to the adsorption process of the present invention.
The carbonyl impurity is in general any contaminant of the oxygenated organic liquid having the carbon-oxygen double bond characteristic of carbonyls. Depending on the specific oxygenated organic liquid, the carbonyl impurities may be ketones, aldehydes, oxides, furans, and the like. In the case of oxygenated liquids comprising a carbonylation product, preferred types of carbonyl impurities are reactive species that are detrimental to the overall quality of the oxygenated organic liquid, as measured using the aforementioned standard permanganate time test (STM. 170). Specifically, saturated and unsaturated aldehyde compounds meet this description. Ketone impurities such as acetone and methyl ethyl ketone, while not significantly affecting the product permanganate time, are also preferably adsorbed since they are often difficult to remove by conventional fractionation.
The carbonyl impurity, however, is not the same class of compound (e.g. carboxylic acid) as the oxygenated organic liquid. It is therefore not recommended to use the adsorption process of the present invention to separate, for example, propionic acid from acetic acid, as this separation is more amenable to distillation. In contrast, the present invention is most effective for the separation of different classes of carbonyls based on their respective differences in reactivity with the resin. Adsorption is especially advantageous over prior art distillation methods when the boiling point of the carbonyl impurity is near that of the oxygenated organic liquid. For example, the adsorption process of the present invention provides a simple and effective solution to the well-known problem of removing crotonaldehyde (b.p. 104xc2x0 C.) from acetic acid (b.p. 118xc2x0 C.).
The carbonyl impurity is present in the oxygenated organic liquid at a level of below about 50% by weight to be considered an impurity. Preferably, the carbonyl impurity concentration is from about 1 part per million (ppm) to about 20% by weight. Directionally, concentrations above this range more quickly expend the resin functional groups. Concentrations of carbonyl impurities below this range generally do not warrant the use of the adsorption method of the present invention. After treatment according to the process of the present invention, the treated liquid stream has a reduced concentration of undesired carbonyl impurities. The effectiveness of the treatment varies, of course, depending on the types of oxygenated organic liquids fed to the process and carbonyl impurities targeted for removal. In a preferred mode of operation corresponding to the treatment of carbonylation product streams (e.g. acetic acid), the treated liquid stream is depleted in carbonyl impurities to the extent that the permanganate time test of this material is at least about 120 minutes. For acetic acid, a permanganate time test result of 120 minutes is normally acceptable to commercial buyers.
As stated, resin-based adsorbents effective for the process of the present invention are generally those having an amine functional group. Without limiting the scope of the invention, it has been theorized that these amine functional groups are capable of reacting or complexing with carbonyl impurities to form an intermediate oximation reaction product or so-called Schiff base that remains affixed to the solid resin structure. For example, AG 4-X4 (available from Bio-Rad Laboratories, Richmond, Calif., a commercial weak anion resin having tertiary amine functional groups on an acrylic matrix, has been found to react with acetaldehyde impurities in an acetic acid stream. The reaction product, ethylideneazanol (an oxime), remains bound to the resin, thus effectively removing the carbonyl impurity according to the present invention. Compared to carrying out the oximation reaction in the liquid phase as outlined in European patent EP 0487284 B1 and U.S. Pat. No. 5783731, adsorption of carbonyl impurities onto a solid phase provides a significantly more convenient alternative. For instance, to costs associated with 1) continual injection of liquid reactant into the process, 2) the use of a homogeneous oximation reactor, and 3) subsequent separation of oximation products by distillation and extraction are all avoided.
In addition to the above mentioned AG 4-X4 resin, essentially any resin having amine functional groups can be used in the process of the present invention. In terms of performance, resins having tertiary amine functional groups are preferred over those having quaternary amine groups. Examples of preferred resins having at least some tertiary amine groups include, but are not limited to, AG 4-X4 and AG 3-X4 from Bio-Rad Laboratories (Richmond, Calif.) and Dowex WGR and Dowex MWA-1 from the Dow Chemical Company (Midland, Mich.).
The adsorption conditions used in the process of the present invention include an absolute pressure at least sufficient to maintain the feed stream as a liquid. In most cases, this absolute operating pressure is from about 0.1 to about 5 atmospheres (about 51 to about 1010 kPa). For convenience, atmospheric pressure is normally chosen. The adsorption temperature is preferably in the range from about 20xc2x0 C. to about 100xc2x0 C. In general, higher temperatures improve the interaction of the carbonyl impurities with the reactive amine functional groups of the resin. However, resin thermal degradation is a concern at temperatures above about 120xc2x0 C. When the preferred continuous flow mode of operation is employed in the adsorption process, a suitable liquid hourly space velocity (LHSV) is in the range from about 0.1 to about 30 hrxe2x88x921. As understood in the art, the LHSV is the hourly volumetric liquid flow rate divided by the resin adsorbent volume and represents the reciprocal of the average time of the liquid within the adsorbent bed.
After an extended period of operation in carbonyl impurity removal service the reactive amine functional groups of the resin are expended through reaction. As substantially all of the amine groups are converted to resin-bound oximes, the resin gradually loses its effectiveness, so that the treated liquid stream may no longer conform to the product quality specifications demanded in terms of its permanganate time or other requirements. At this point, the resin has substantially reached its adsorption capacity and a simple regeneration procedure can restore its activity. Of course, resin regeneration may also be used even when the resin has only partially reached its adsorption capacity, but the economics of the operation in this case are generally less desirable.
Regeneration requires subjecting the resin, either in situ or ex situ, to a basic solution capable of restoring the resin amine functional groups while washing the adsorbed species from the resin as carbonyl compounds. Because the resin functional groups are re-established, the resin will again exhibit activity for carbonyl impurity removal. The regeneration procedure can be repeated multiple times to vastly extend the resin life. Regarding the mechanics of changing between the adsorption and regeneration phases of the present invention, it is possible to use swing-bed systems of the prior art to alternate beds of adsorbent between the adsorption and regeneration modes of operation. This will ensure a continual availability of active resin for the adsorption of carbonyl impurities.
The basic solution used for regenerating the resin after having partially or substantially reached its adsorption capacity can comprise an aqueous or an organic solution. Aqueous solutions are normally the most economical, with solutions of bases selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, and sodium bicarbonate being preferred. Sodium hydroxide is especially preferred. For purposes of regenerating the resin, concentrations of aqueous basic solutions in the range from about 0.01 to about 5 molar (or moles of base per liter of solution) are preferred. Below this range, an unnecessarily large amount of solution is required to regenerate the adsorbent. Above this range, the base concentration may be sufficiently strong to have a detrimental effect on the resin structure. For example, after the resin has undergone a period of service in the adsorption process of the present invention, a strong caustic solution can potentially attack the resin, destroying its functional groups, rather than restoring the amine function.
Other solutions that are effective for regenerating the resin include organic bases. Preferred types generally fall into the category of so-called xe2x80x9chindered aminexe2x80x9d bases having secondary or tertiary amine groups. Examples of such organic bases include, but are not limited to, trimethylamine, triethylamine, pyrrolidine, piperidine, morpholine, piperazine, dialkylamines (e.g. diethylamine and n- and i-propylamine), pyridine, and all isomers of picoline. The organic bases may be used in pure form or diluted with a diluent such as water in which the organic base is at least partially soluble.
The regeneration of resin that has partially or substantially reached its adsorption capacity involves removing it from adsorption service and subjecting it to any of the above-mentioned basic solutions. It is not advisable to contact the base directly with a resin that is solvated with or immersed in an acidic solution such as acetic acid, since the resulting acid-base reaction could cause excessive heat release and damage the resin bed. Rather, an intermediate wash fluid such as water or other solution with a pH in the range from about 4 to about 10 should be used to rinse acidic media from the resin prior to regeneration. Water is normally preferred for convenience. During the rinsing with intermediate wash fluid, it is recommended to monitor the effluent solution pH to establish that essentially all acid is removed prior to subjecting the resin to the basic regeneration solution. In most cases, allowing the resin to dry between the adsorption and regeneration phases should be avoided to prevent problems associated with shrinkage/swelling of the resin bed.
This contacting of the resin with a base can be performed according to any means known in the art such as continuous flow or batchwise contacting. Continuous flow contacting through a fixed bed of the resin that has either partially or substantially reached its adsorption capacity is preferred. In this case, the flow rate of liquid base would be in accordance with a liquid hourly space velocity from about 0.1 to about 30 hrxe2x88x921. Other conditions associated with the regeneration procedure include a temperature from about 20xc2x0 C. to about 100xc2x0 C. and a pressure from about 0.1 to about 5 atmospheres. Ambient conditions of pressure and temperature are normally chosen for convenience.
It is within the scope of the invention to use a number of pre- or post-treatment steps in combination with carbonyl impurity adsorption to provide a high purity treated liquid stream. For example, when the process is used for the treatment of carbonyl impurity contaminated acetic acid that is produced by methanol carbonylation, metal cations may also be present in the acid. These cations are known contaminants originating from reaction catalysts (e.g. Rh+3) or co-catalysts (e.g. Li+1) or corrosion of the plant metallurgy (e.g. Co+2). The removal of undesired cations in this case is taught in U.S. Pat. No. 5344976, hereby incorporated by reference. As described in this patent, a number of strong acid cation exchange resins, including Amberlyst(copyright) 15 (available from Rohm and Haas Company, Philadelphia, Pa.) are suitable and normally used in their hydrogen form.
Also pertaining to the treatment of commercial acetic acid streams is the need to remove molecular iodine and hydrogen iodide that result from the use of iodine-containing catalyst promoters in the reaction environment. The removal of these components may therefore also be combined with the carbonyl impurity adsorptive removal process of the present invention. For the removal of iodine and hydrogen iodide, the prior art teaches the use of various anion exchange resins, such as Reillex(copyright) 425, a crosslinked polyvinylpyridine (available from Reilly Industries, Indianapolis, Ind. USA), Deloxan(copyright) THP (available from Degussa AG, Frankfurt, Germany), or Amberlite(copyright) IRA-958 (available from Rohm and Haas Company, Philadelphia, Pa., USA). The prior art also discloses the use of carbonaceous material, including activated carbons, activated carbon fiber, wood charcoal, bone char, lignite, and others that may be impregnated with alkali metals known to increase the inorganic iodine compound chemisorption capacity.
Another consideration related to the purification of acetic acid derived from methanol carbonylation is the removal of alkyl iodides and other iodine-containing compounds. The prior art also teaches this type of purification, which may be combined with the process of the present invention. U.S. Pat. No. 4,615,806, for example, discloses the use of silver exchanged resins for this service, while U.S. Pat. No. 5,962,735 teaches the use of silver exchanged zeolites.
Regardless of the use of any pre- or post-treatment steps, a significant objective of the treatment process of the present invention is to provide a treated product stream having quality attributes in terms of its permanganate test time and overall purity that render it suitable for further processing. As mentioned, for acetic acid in particular, two major uses are as a precursor for vinyl acetate monomer (VAM) production and as a solvent in the manufacture of purified terephthalic acid (PTA). The VAM process is well known in the art and described, among other references, in U.S. Pat. No. 5,990,344. The PTA process is also well know and described in, for example, U.S. Pat. No. 5,200,557, where acetic acid is a specific type of aliphatic carboxylic acid useful as a solvent in the reaction environment. Thus, in the case where acetic acid is purified according to the present invention to remove carbonyl impurities, it is contemplated that the treated liquid steam may be used in either a VAM or a PTA production process.
The adsorption process of the present invention may be carried out in any number of modes of operation. For example, the adsorption step can be performed using a fixed-,moving-, or fluidized-bed system or a batch operation. It is preferred to employ a fixed-bed system with the oxygenated organic liquid feed stream containing a carbonyl impurity continually flowing through the adsorption zone of active resin. Of course, the adsorption may also comprise a plurality of resin beds with the desired conditions maintained between and within the separate beds. The mechanics of this type of operation are known in the art.

Adsorptive removal of carbonyl impurities from oxygenated organic liquids


A polymer heart valve has a leaflet with a base geometry of a cylinder for simplicity and effective opening. A helical swept surface is added to the top of the cylinder to enhance stable coaption. The heart valve includes a plurality of flexible leaflets. Each leaflet includes a top portion and a bottom portion. The bottom portion is an axial section of a cylinder having an axis and a radius. A first section of the top portion is a surface defined by a first arc having a first radius swept along a first helix. The first arc is tangent to the axial section of the cylinder. A second section of the top portion is a surface defined by a second arc having a second radius swept along a second helix. The second arc is tangent to the axial section of the cylinder. The second helix is a left-handed helix having the same radius and axis as the cylinder.

The disclosures herein relate generally to prosthetic heart valves and more particularly to tri-leaflet prosthetic heart valves having polymeric valve leaflets.
Prosthetic heart valves for human patients have been available since the 1950s, following the advent of blood oxygenators, which made open heart surgery possible. Today, there are three general types of prosthetic heart valves, including mechanical valves, tissue valves and polymer valves. A heart valve prosthesis is implanted into an annular opening in a patient""s heart following surgical removal of a diseased or damaged natural valve. The valve can be secured in the annulus of the opening through the use of sutures or pins that penetrate the host tissue and an outside edge of the valve. Alternatively, the valve can be secured in the annulus by suturing the host tissue to a sewing ring. Heart valves function essentially as one-way check valves for blood flow through the beating heart.
The term xe2x80x9cmechanical valvexe2x80x9d as used herein refers to bi-leaflet heart valves comprising a valve orifice fabricated at least in part of a rigid, biologically compatible material such as pyrolytic carbon, and comprising essentially no biological components. The term xe2x80x9cbioprosthetic valvexe2x80x9d refers to a bi-leaflet or tri-leaflet heart valve comprising at least some biological components such as tissue or tissue components. The biological components of tissue valves are obtained from a donor animal (typically bovine or porcine), and the valve may comprise either biological materials alone or biological materials with man-made supports or stents. The term xe2x80x9cpolymeric valvexe2x80x9d refers to a tri-leaflet or bi-leaflet heart valve comprising at least some elastomeric polymer components, including at least elastomeric polymer valve leaflets.
A bi-leaflet mechanical valve typically comprises an annular valve body in which two opposed leaflet occluders are pivotally mounted. The occluders are typically rigid, although some designs incorporate semi-rigid leaflets, and the occluders move between a closed position, in which the two leaflets are mated and block blood flow in the reverse direction, and an open position, in which the occluders are pivoted away from each other and do not block blood flow in the forward direction. The energy of blood flow causes the occluders to move between their open and closed positions.
Flexible heart valves seal against reverse flow by having leaflets whose total surface area is greater than the area of the orifice. Sections of the leaflets, therefore, contact one another, or coapt, to close the valve and prevent blood backflow. Coaptive sealing occurs over an area on the leaflets, rather than merely along their edges. Two leaflets are unlikely to seal with any stability if they only contact line to line. This can cause T-boning, or prolapse. T-boning occurs when the end of one leaflet slips below the end of the mating leaflet during closing, forming a line-on-line contact rather than an area contact.
Although both tissue and polymer valves involve flexible leaflets, the degree of control possible for the shape of tissue valve leaflets is extremely small, since the leaflets are formed from tissue sheets that are trimmed and sewn to a valve stent. Polymer valves, on the other hand, may be fabricated by molding, casting, and other known techniques, and therefore allow much greater control of valve body and leaflet shape. By precise control of the leaflet shape, polymer heart valves may be fabricated with improved wear and performance characteristics. In particular, by providing leaflets having an analytic shape in a selected position which can be represented generally by analytic geometry. An analytic shape may include a portion of a cylindrical surface, of an ellipsoid, of a paraboloid, or of another shape that can be defined mathematically.
A tri-leaflet heart valve prosthesis typically comprises an annular valve body and three flexible leaflets attached thereto. The valve body comprises an annular base and three leaflet support posts. A sewing ring annularly coupled to the periphery of the valve body provides a place for sutures to be applied when the valve is implanted. The leaflets are attached to the three shaped posts along an attachment curve, and they also each have a free, unattached edge remote from the attachment curve. The place where two adjacent leaflets come together at one of the support posts is called the commissure, and the generally curved area on the leaflet between the free edge and the attachment curve is known as the belly of the leaflet. The free edges of the three leaflets come together at a xe2x80x9ctriple pointxe2x80x9d generally on the axis of the valve.
One aspect of the sealing problem for tri-leaflet polymer valves arises from the nature of the valve geometry. As already noted, it is desirable to provide leaflets defined by an analytical shape. Tradeoffs must be made, however, among various possible geometries. In particular, it is desirable to provide a coaption surface that seals efficiently and robustly. Many prior art approaches to the difficult problem of leaflet design have been made.
U.S. Pat. No. 4,888,009 shows a prosthetic heart valve comprising leaflets of a spherical section, with no additional coaption surface. While this design is simple to fabricate, provides relatively good fabrication control, and has a small gap between leaflets, the vertical component of the angle between the surface tangents of opposed leaflets is not constant. For example, at the triple point and commissures, the leaflet surface tangent is nearly vertical, so the angle between the surface tangents of opposed leaflets is small and an effective and robust seal is facilitated in these regions. However, at the midpoint of the leaflet free edge between the commissures and the triple point, the leaflet surface tangent is much further from vertical. Consequently, the angle between the surface tangents of opposed leaflets is large, and the seal may not be effective or robust. Small deviations in position or load might disrupt the sealing of the leaflets and cause one free margin to slide below the other. The leaflets would have a line of contact instead of an area of contact.
Coaptive surfaces at the ends of the leaflet can be used to prescribe the angle between the surface tangents at the ends of opposing leaflets. The simplest shape for a coaptive surface is to have a vertical surface (i.e., a surface oriented generally parallel to the direction of blood flow) at the end of each leaflet. Such surfaces appear to be vertically aligned when the valve is in the closed position. For a tri-leaflet valve with identical leaflets, two vertical coaption surfaces are actually needed on each leaflet because each leaflet covers 120 degrees (not 180), and the leaflets must bend inward from the commissure to the triple point before again bending back to the other commissure (see FIG. 3). Tri-leaflet valves having vertical coaption surfaces, therefore, all have three general surface areas: the belly of the leaflet and the two coaptive surfaces. Many leaflet belly surface configurations have been proposed (with and without vertical coaption surfaces). Tri-leaflet valves having vertical coaption surfaces all suffer from a particular problem. Although the sealing of two vertical surfaces is effective, the discontinuous crease which transitions the coaptive surface to the leaflet belly resists the reverse buckling needed to open the valve. The result is high opening pressures and high pressure drops across the open valve.
In addition to leaflets comprising a single analytical shape, attempts have been made to improve valve performance by fabricating leaflets comprising more than one analytical shape. In this regard, WO 98/32400 provides a valve having leaflets comprising a cylindrical section and having a spherical coaption end. The transition from the leaflet belly to the coaption surface is made by revolving an arc around an axis to form a spherical coaption area. In addition, the specific shape chosen allows the surface tangencies at the leaflet free edges to be vertical. The designers conclude that bidirectional curvature in the leaflet belly produces poor opening characteristics, and that leaflets with only one degree of curvature in the belly are superior. Although the WO 98/32400 valve provides better performance than a fully spherical leaflet or a fully cylindrical leaflet, the valve has relatively large gaps at the triple point and the commissure.
General engineering experience with tissue and polymer heart valves have established a number of criteria for these valves, including:
1) A coaption surface which extends from the triple point to the commissure.
2) A coaption surface which is tangent to the belly geometry at its bottom and nearly vertical at its top.
3) A simple, singly curved leaflet belly.
4) A height short enough to fit into the natural anatomy.
5) A small gap area between leaflets to reduce regurgitation.
Cylindrical leaflets with revolved leaflet end sections e.g. spheres and toroids, produce adequate topological solutions for only a limited range of valve heights and gap areas. Given the limitations of existing leaflet geometries, it is desirable to have a valve leaflet defined by an analytic shape that provides a smooth transition surface from the leaflet belly to the coaption area, but which avoid large gaps at the commissures and the triple point. Analytical shapes suggested in the prior art have not achieved these goals. Therefore, what is needed is a new valve surface topology with more degrees of freedom so that a shorter valve with a small gap area, a cylindrical leaflet, and a tangent coaptive surface can be produced.
It has been discovered that a heart valve with leaflets having a helical swept coaption surface provides advantages not obtained from prior art analytical leaflet shapes. In one embodiment, accordingly, the present invention provides a valve leaflet having a base portion geometry comprising a cylindrical section and a top portion geometry comprising a swept helix. To this end, a heart valve includes a plurality of flexible leaflets. Each leaflet includes a top portion and a bottom portion. The bottom portion is a cylinder having an axis, a radius and an axial section. A first section of the top portion is a surface defined by a first arc swept along a first helix. The first helix is a right handed helix having the same radius and axis as the cylinder. A second section of the top portion is a surface defined by a second arc swept along a second helix. The second helix is a left handed helix having the same radius and axis as the cylinder.

Polymer heart valve with helical coaption surface


An imaging member, such as a negative-working printing plate or on-press cylinder, can be prepared using a hydrophilic imaging layer comprised of a heat-sensitive hydrophilic polymer that comprises recurring units comprising quaternary ammonium carboxylate groups. These quaternary ammonium carboxylate groups include at least one substituted-alkylene(C1-C3)-phenyl group. The imaging member can also include an infrared radiation sensitive material to provide added sensitivity to heat that can be supplied by laser irradiation in the IR region. The heat-sensitive polymer is considered xe2x80x9cswitchablexe2x80x9d in response to heat, and provides a lithographic image without wet processing.

This invention relates in general to lithographic printing plates and specifically to lithographic printing plates that require no wet processing after imaging. The invention also relates to a method of digitally imaging such imaging members, and to a method of printing using them.
The art of lithographic printing is based upon the immiscibility of oil and water, wherein an oily material or ink is preferentially retained by an imaged area and the water or fountain solution is preferentially retained by the non-imaged areas. When a suitably prepared negative working printing plate is moistened with water and ink is then applied the background or non-imaged areas retain the water and repel the ink while the imaged areas accept the ink and repel the water. The reverse holds true for positive working plates, in which the background is imaged. The ink is then transferred to the surface of a suitable substrate, such as cloth, paper or metal, thereby reproducing the image.
Very common lithographic printing plates include a metal or polymer support having thereon an imaging layer sensitive to visible or UV light. Both positive and negative-working printing plates can be prepared in this fashion. Upon exposure, and perhaps post-exposure heating, either imaged or non-imaged areas are removed using wet processing chemistries.
Thermally sensitive printing plates are less common, yet represent a steadily growing market. Currently, most of these plates utilize similar materials and similar imaging mechanisms as UV-imageable plates. For example, a thermal acid generator might be used in lieu of a photoacid generator and the same series of preheat and development steps might be employed. The main advantage of these digital plates is that the thermal imaging process is rapid and inexpensive compared to the analog process involving the creation of a mask and blanket UV exposure. Examples of such plates are described in U.S. Pat. No. 5,372,915 (Haley et al). They include an imaging layer comprising a mixture of dissolvable polymers and an infrared radiation absorbing compound. While these plates can be imaged using lasers and digital information, they require wet processing using alkaline developer solutions.
It has been recognized that a lithographic printing plate could be created by ablating an IR absorbing layer. For example, Canadian 1,050,805 (Eames) discloses a dry planographic printing plate comprising an ink receptive substrate, an overlying silicone rubber layer, and an interposed layer comprised of laser energy absorbing particles (such as carbon particles) in a self-oxidizing binder (such as nitrocellulose). Such plates were exposed to focused near IR radiation with a Nd++YAG laser. The absorbing layer converted the infrared energy to heat thus partially loosening, vaporizing or ablating the absorber layer and the overlying silicone rubber. The plate was developed by applying naphtha solvent to remove debris from the exposed image areas. Similar plates are described in Research Disclosure 19201, 1980 as having vacuum-evaporated metal layers to absorb laser radiation in order to facilitate the removal of a silicone rubber overcoated layer. These plates were developed by wetting with hexane and rubbing. CO2 lasers are described for ablation of silicone layers by Nechiporenko and Markova, PrePrint 15th International IARIGAI Conference, June 1979, Lillehammer, Norway, Pira Abstract 02-79-02834. Typically, such printing plates require at least two layers on a support, one or more being formed of ablatable materials. Other publications describing ablatable printing plates include U.S. Pat. No. 5,385,092 (Lewis et al), U.S. Pat. No. 5,339,737 (Lewis et al), U.S. Pat. No. 5,353,705 (Lewis et al), U.S. Pat. No. Reissue 35,512 (Nowak et al) and U.S. Pat. No. 5,378,580 (Leenders).
While the noted printing plates used for digital, processless printing have a number of advantages over the more conventional photosensitive printing plates, there are a number of disadvantages with their use. The process of ablation creates debris and vaporized materials that must be collected. The laser power required for ablation can be considerably high, and the components of such printing plates may be expensive, difficult to coat, or unacceptable in resulting printing quality. Such plates generally require at least two coated layers on a support.
One approach toward non-process, non-ablation printing plates involves the use of xe2x80x9cswitchable polymers.xe2x80x9d These polymers will undergo thermally driven chemical reactions in which highly polar moieties are either created or destroyed under imaging conditions. This results in the storage of the imaging data as hydrophilic and hydrophobic regions of a continuous polymer surface. In addition to not needing wet processing, such plates have the advantage of not needing any type of material collection devices which ablation-based plates require. Also unlike ablation plates, a switchable polymer plate in its ideal form would consist of one layer and can be manufactured on a single pass through a coating machine.
U.S. Pat. No. 4,034,183 (Uhlig) describes the use of high powered lasers to convert hydrophilic surface layers to hydrophobic surfaces. A similar process is described for converting polyamic acids into polyimides in U.S. Pat. No. 4,081,572 (Pacansky). The use of high-powered lasers is undesirable in the industry because of their power requirements and because of their need for cooling and frequent maintenance.
U.S. Pat. No. 4,634,659 (Esumi et al) describes imagewise irradiating hydrophobic polymer coatings to render exposed regions more hydrophilic in nature. While this concept was one of the early applications of converting surface characteristics in printing plates, it has the disadvantages of requiring long UV light exposure times (up to 60 minutes), and the plate""s use is in a positive-working mode only.
U.S. Pat. No. 4,405,705 (Etoh et al) and U.S. Pat. No. 4,548,893 (Lee et al) describe amine-containing polymers for photosensitive materials used in non-thermal processes. The imaged materials also require wet processing after imaging.
Thermal processes using polyamic acids and vinyl polymers with pendant quaternary ammonium groups are described in U.S. Pat. No. 4,693,958 (Schwartz et al), but wet processing is required after imaging. In addition, the polyamic acid switchable polymers in this invention show low discrimination magnitude and the quaternary ammonium-based examples suffer from wash-off problems of both the foreground and the background.
U.S. Pat. No. 5,512,418 (Ma) describes the use of polymers having cationic quaternary ammonium groups that are heat-sensitive. However, like most of the materials described in the art, wet processing is required after imaging.
WO 92/09934 (Vogel et al) describes photosensitive compositions containing a photoacid generator and a polymer with acid labile tetrahydropyranyl or activated ester groups. However, imaging of these compositions converts the imaged areas from hydrophobic to hydrophilic in nature and the imaged areas are prone to scumming.
In addition, EP-A 0 652 483 (Ellis et al) describes lithographic printing plates imageable using IR lasers, and which do not require wet processing. These plates comprise an imaging layer that becomes more hydrophilic upon imagewise exposure to heat. This coating contains a polymer having pendant groups (such as t-alkyl carboxylates) that are capable of reacting under heat or acid to form more polar, hydrophilic groups. Imaging such compositions converts the imaged areas from hydrophobic to relatively more hydrophilic in nature, and thus requires imaging the background of the plate, which is generally a larger area. This can be a problem when imaging to the edge of the printing plate is desired. As with the plates described in WO 92/09934, the plates described in Ellis et al are also prone to scumming.
Although a number of switchable polymer-based printing plates are known, there remain technical barriers toward the utilization of this technology in commercially feasible products. Three difficulties commonly experienced in the design of switchable polymer-based plates are physical wear of the plates, and the related problems of background scumming and blanket toning.
xe2x80x9cPhysical wearxe2x80x9d refers to the mechanical degradation of a printing plate during the printing process. Sufficient resistance to physical wear is often the major factor in determining whether or not a printing plate will be useful for press runs of very long length.
The problems of scumming (also known as xe2x80x9ctoningxe2x80x9d) and blanket toning typically result if ink-rejecting areas of the plate are not sufficiently polar. The uptake of ink in undesired areas of the plate results in the consequent undesirable transfer of ink to the final prints. This manifests itself as an unwanted gray or black color in background areas of the final prints. Scumming may occur in both negative-working plates (in nonimaged areas) and positive plates (in imaged areas). The related problem of blanket toning refers to the buildup of ink in the background areas of the printing press blanket cylinder. Excessive blanket toning results in the necessity of periodically stopping a press run to manually clean the ink from the blanket. This can have a negative impact on the productivity of a printing process.
In conventional developable printing plates, grained, anodized aluminum has proven to be a reliable background substrate. It is mechanically tough and shows little evidence of wear even on very long press runs. The material can also tolerate a wide range of press conditions without showing scumming or excessive blanket toning. Generally, the imaging process imparts a change in solubility to the imaged areas of the plate such that, after wet development, a grained, anodized aluminum surface is selectively exposed. Switchable polymer-based plates, however, are designed such that no portions of the imageable layer of the plate are removed. Thus the favorable background properties of an aluminum support substrate cannot be utilized. Not surprisingly, scumming behavior has been observed in many of the switchable polymer-based plates that have been reported in the patent literature.
In EP-A 0 924 102, it is reported that scumming may occur with some known printing plates containing switchable polymers in the imaging layers.
In switchable polymer-based printing plates, a major challenge lies in the creation of a synthetic polymer surface that has both adequate physical toughness and resistance to toning. In general, surfaces that reject ink well tend to be very highly hydrophilic and thus when exposed to an aqueous fountain solution they may be dissolved and lose adhesion to the support substrate. Alternatively, they may swell and become prone to abrasion and wear. It can be expected, then, that many of the synthetic polymer surfaces that are most resistant to toning will also have inherently inadequate physical properties for use in long-run printing plates. It is not uncommon that approaches to improve a switchable polymer plate""s scumming behavior by increasing the hydrophilicity of the imageable layer will result in a consequent decrease in the wear resistance of the plate. Similarly, efforts to improve the physical toughness of a plate can result in an increase in scumming propensity.
Copending U.S. Ser. No. 09/454,151 noted above describes and claims negative-working imaging members that overcome the problems noted above and provide clean backgrounds, minimal blanket toning and improved resistance to wear. While the heat-switchable polymers described therein provide a significant advance in the art, even further improvements are desired in imaging speed and shorter roll-up values.
Improvements in heat-switchable imaging members are provided by using a specific class of heat-sensitive, switchable polymers that provide a good balance of physical toughness with resistance to scumming and blanket toning when incorporated into an imaging member. They also exhibit increased imaging speeds.
The switchable polymers can be obtained by simply reacting any of the carboxylic acid-containing polymers (or polymers containing equivalent groups, such as anhydrides) with a quaternary ammonium hydroxide that contains a substituted-alkylene(C1-C3)-phenyl group. The heat-sensitive polymer, when formulated with a photothermal conversion material and preferably a crosslinking agent, provides a mechanically durable infrared radiation sensitive imaging member that exhibits excellent resistance to scumming and blanket toning.
One embodiment of the present invention is an imaging member comprising a support having thereon a hydrophilic imaging layer comprising a hydrophilic heat-sensitive polymer comprising recurring units that comprise quaternary ammonium carboxylate groups containing at least one substituted-alkylene(C1-C3)-phenyl group.
This invention also provides a method of imaging comprising the steps of:
A) providing the imaging member described above, and
B) imagewise exposing the imaging member to energy to provide exposed and unexposed areas in the imaging layer and the imaging member, whereby the exposed areas are rendered more oleophilic than the unexposed areas by heat provided by the imagewise exposing.
In addition, the method of imaging can be extended to be a method of printing by following steps A and B with a further step of
C) in the presence of water or a fountain solution, contacting the imagewise exposed imaging member with a lithographic printing ink, and imagewise transferring the ink to a receiving material.
The ammonium cations used in the heat-sensitive polymers include one or more substituted-alkylene(C1-C3)-phenyl groups (preferably benzyl groups), and the result is improved imaging speed and roll-up over many of the heat-sensitive polymers described in U.S. Ser. No. 09/454,151 (noted above) that do not have such groups. The one or more noted alkylenephenyl groups comprise one or more substituents on either or both of the alkylene and phenyl moieties. As described in more detail below, the substitution can be of any of a wide variety of patterns and chemical components.
The imaging member (for example, printing plates) of this invention have improved mechanical durability over other xe2x80x9cswitchable polymerxe2x80x9d processless printing plates described in the literature.
The imaging members of this invention comprise a support and one or more layers thereon that are heat-sensitive. The support can be any self-supporting material including polymeric films, glass, ceramics, metals or stiff papers, or a lamination of any of these materials. The thickness of the support can be varied. In most applications, the thickness should be sufficient to sustain the wear from printing and thin enough to wrap around a printing form. A preferred embodiment uses a polyester support prepared from, for example, polyethylene terephthalate or polyethylene naphthalate, and having a thickness of from about 100 to about 310 xcexcm. Another preferred embodiment uses aluminum foil having a thickness of from about 100 to about 600 xcexcm. The support should resist dimensional change under conditions of use.
The support can also be a cylindrical surface having the heat-sensitive polymer composition thereon, and thus being an integral part of the printing press. The use of such imaged cylinders is described for example in U.S. Pat. No. 5,713,287 (Gelbart).
The support may be coated with one or more xe2x80x9csubbingxe2x80x9d layers to improve adhesion of the final assemblage. Examples of subbing layer materials include, but are not limited to, gelatin and other naturally occurring and synthetic hydrophilic colloids and vinyl polymers (such as vinylidene chloride copolymers) known for such purposes in the photographic industry, vinylphosphonic acid polymers, silicon-based sol-gel materials, such as those prepared from alkoxysilanes such as aminopropyltriethoxysilane or glycidoxypropyltriethoxysilane, titanium sol gel materials, epoxy functional polymers, and ceramics.
The backside of the support may be coated with antistatic agents and/or slipping layers or matte layers to improve handling and xe2x80x9cfeelxe2x80x9d of the imaging member.
The imaging members, however, have preferably only one heat-sensitive layer that is required for imaging. This hydrophilic layer includes one or more heat-sensitive polymers, and optionally but preferably a photothermal conversion material (described below), and preferably provides the outer printing surface of the imaging member. Because of the particular polymer(s) used in the imaging layer, the exposed (imaged) areas of the layer are rendered more oleophilic in nature.
The heat-sensitive polymers useful in this invention comprise random recurring units at least some of which comprise particular quaternary ammonium salts of carboxylic acids. The polymers generally have a molecular weight of at least 3,000 Daltons and preferably of at least 20,000 Daltons.
The polymer randomly comprises one or more types of carboxylate-containing recurring units (or equivalent anhydride units) units identified as xe2x80x9cAxe2x80x9d below in Structure 1 and optionally one or more other recurring units (non-carboxylated) denoted as xe2x80x9cBxe2x80x9d in Structure 1.
The carboxylate-containing recurring units are linked directly to the polymer backbone which is derived from the xe2x80x9cAxe2x80x9d monomers, or are connected by spacer units identified as xe2x80x9cXxe2x80x9d in Structure 1 below. This spacer unit can be any divalent aliphatic, alicyclic or aromatic group that does not adversely affect the polymer""s heat-sensitivity. For example, xe2x80x9cXxe2x80x9d can be a substituted or unsubstituted alkylene group having 1 to 16 carbon atoms (such as methylene, ethylene, isopropylene, n-propylene and n-butylene), a substituted or unsubstituted arylene group having 6 to 10 carbon atoms in the arylene ring (such as m- or p-phenylene and naphthylenes), substituted or unsubstituted combinations of alkylene and arylene groups (such arylenealkylene, arylenealkylenearylene and alkylenearylenealkylene groups), and substituted or unsubstituted N-containing heterocyclic groups. Any of these defined groups can be connected in a chain with one or more amino, carbonamido, oxy, thio, amido, oxycarbonyl, aminocarbonyl, alkoxycarbonyl, alkanoyloxy, alkanoylamino or alkaminocarbonyl groups. Particularly useful xe2x80x9cXxe2x80x9d spacers contains an ester or amide connected to an alkylene group or arylene group (as defined above), such as when the ester and amide groups are directed bonded to xe2x80x9cAxe2x80x9d.
Additional monomers (non-carboxylate monomers) that provide the recurring units represented by xe2x80x9cBxe2x80x9d in Structure 1 above include any useful hydrophilic or oleophilic ethylenically unsaturated polymerizable comonomers that may provide desired physical or printing properties of the surface imaging layer or which provide crosslinkable functionalities. One or more xe2x80x9cBxe2x80x9d monomers may be used to provide these recurring units, including but not limited to, acrylates, methacrylates, styrene and its derivatives, acrylamides, methacrylamides, olefins, vinyl halides, vinyl ethers, and any monomers (or precursor monomers) that contain carboxy groups (that are not quaternized).
The quaternary ammonium carboxylate-containing polymer may be chosen or derived from a variety of polymers and copolymer classes including, but not necessarily limited to polyamic acids, polyesters, polyamides, polyurethanes, silicones, proteins (such as modified gelatins), polypeptides, and polymers and copolymers based on ethylenically unsaturated polymerizable monomers such as acrylates, methacrylates, acrylamides, methacrylamides, vinyl ethers, vinyl esters, alkyl vinyl ethers, maleic acid/anhydride, itaconic acid/anhydride, styrenics, acrylonitrile, and olefins such as butadiene, isoprene, propylene, and ethylene. A parent carboxylic acid-containing polymer (that is, one that is reacted to form quaternary ammonium carboxylate groups) may contain more than one type of carboxylic acid-containing monomer. Certain monomers, such as maleic acid/anhydride and itaconic acid/anhydride may contain more than one carboxylic acid unit. Preferably, the parent carboxylic acid-containing polymer is an addition polymer or copolymer containing acrylic acid, methacrylic acid, maleic acid or anhydride, or itaconic acid or anhydride or a conjugate base or hydrolysis product thereof.
In Structure 1, n represents about 25 to 100 mol % (preferably from about 50 to 100 mol %), and m represents 0 to about 75 mol % (preferably from 0 to about 50 mol %).
While Structure 1 could be interpreted to show polymers derived from only two ethylenically unsaturated polymerizable monomers, it is intended to include terpolymers and other polymers derived from more than two monomers.
The quaternary ammonium carboxylate groups must be present in the heat-sensitive polymer useful in this invention in such a quantity as to provide a minimum of one mole of the quaternary ammonium carboxylate groups per 1000 g of polymer and a maximum of one mole of quaternary ammonium carboxylate groups per 45 g of polymer. Preferably, this ratio (moles of quaternary ammonium carboxylate groups to grams of polymer) is from about 1:500 to about 1:45 and more preferably, this ratio is from about 1:300 to about 1:45. This parameter is readily determined from a knowledge of the molecular formula of a given polymer (and the monomeric starting materials) or standard titrimetric or spectrometric methods.
The quaternary ammonium counterion of the carboxylate functionalities may be any ammonium ion in which the nitrogen is covalently bound to a total of four alkyl or aryl substituents as defined below, provided at least one of the four substituents is a substituted-alkylene(C1-C3)phenyl group.
More particularly, in Structure 1 noted above, R1, R2 and R3 are independently substituted or unsubstituted alkyl groups having 1 to 12 carbon atoms [such as methyl, ethyl, n-propyl, isopropyl, 1-butyl, hexyl, methoxy, trichloromethyl, hydroxyethyl, 2-propanonyl, ethoxycarbonymethyl, benzyl, substituted benzyl (such as 4-methoxybenzyl, o-bromobenzyl, and p-trifluoromethylbenzyl), and cyanoalkyl], or substituted or unsubstituted aryl groups having 6 to 14 carbon atoms in the carbocyclic ring (such as phenyl, naphthyl, xylyl, p-methoxyphenyl, p-methylphenyl, m-methoxyphenyl, p-chlorophenyl, p-methylthiophenyl, p-N,N- dimethylaminophenyl, methoxycarbonylphenyl and cyanophenyl). Alternatively, any two or all three of R1, R2 and R3 can be combined to form a ring (or two rings for four substituents) with the quaternary nitrogen atom, the ring having 5 to 14 carbon, oxygen, sulfur and nitrogen atoms in the ring. Such rings include, but are not limited to, morpholine, piperidine, pyrrolidine, carbazole, indoline and isoindoline rings. The nitrogen atom can also be located at the tertiary position of the fused ring. Other useful substituents for these various groups would be readily apparent to one skilled in the art, and any combinations of the expressly described substituents are also contemplated.
Alternatively, multi-cationic ionic species containing more than one quaternary ammonium unit covalently bonded together and having charges greater than +1 (for example +2 for diammonium ions, and +3 for triammonium ions) may be used in this invention.
Preferably, R1, R2 and R3 are independently linear or branched unsubstituted alkyl groups of 1 to 3 carbon atoms, or linear or branched hydroxyalkyl groups of 1 to 3 carbon atoms that comprise 1 to 3 hydroxy groups as the only substituents (generally only one hydroxy group per carbon atom). More preferably, these radicals are independently methyl, hydroxymethyl, ethyl, 2-hydroxyethyl, 1-hydroxyethyl or 1,2-dihydroxyethyl and most preferably, they are either methyl or 2-hydroxyethyl.
R4 is a substituted alkylenephenyl group that has at least one substituent on either the alkylene or phenyl moiety of the group. More preferably, the one or more substituents are on the phenyl moiety. The alkylene moiety can be linear or branched in nature and has from 1 to 3 carbon atoms (such as methylene, ethylene, n-propylene or isopropylene). Preferably, the alkylene moiety of R4 has 1 or 2 carbon atoms and more preferably, it is methylene. The alkylene moiety can have as many substituents as there are available hydrogen atoms to be removed from a carbon atom. Useful alkylene substituents are the same as those described below in defining the phenyl substituents, but the most preferred substituents for the alkylene moiety are fluoro and alkoxy.
The phenyl moiety of R4 can have from 1 to 5 substituents in any useful substitution pattern. Useful substituents include but are not limited to, halo groups (such as fluoro, chloro, bromo, and iodo), substituted or unsubstituted alkyl groups having from 1 to 12 carbon atoms (such as methyl, ethyl, isopropyl, t-butyl, n-pentyl and n-propyl) that can be further substituted with any of the substituents listed herein (such as haloalkyl groups including trihalomethyl groups), substituted or unsubstituted alkoxy groups having 1 to 12 carbon atoms (such as methoxy, ethoxy, isopropoxy, n-pentoxy and n-propoxy), cyano, nitro, substituted or unsubstituted aryl groups having 6 to 14 carbon atoms in the aromatic carbocyclic ring (as defined above for R1, R2 and R3), substituted or unsubstituted alkyleneoxycarbonyl groups having 2 to 12 carbon atoms (such as methyleneoxycarbonyl, ethyleneoxycarbonyl and i-propyleneoxycarbonyl), substituted or unsubstituted alkylcarbonyloxy groups having 2 to 12 carbon atoms (such as methylenecarbonyloxy, ethylenecarbonyloxy and isopropylenecarbonyloxy), substituted or unsubstituted alkylcarbonyl groups having 2 to 12 carbon atoms (such as methylenecarbonyl, ethylenecarbonyl and isopropylenecarbonyl), amido groups, aminocarbonyl groups, trihalomethyl groups, perfluoroalkyl groups, formyl, mercapto and substituted or unsubstituted heterocyclic groups having 5 to 14 atoms in the ring that includes one or more nitrogen, sulfur, oxygen or selenium atoms with the remainder being carbon atoms (such as pyridyl, oxazolyl, thiphenyl, imidazolyl, and piperidinyl).
Preferably, R4 contains 1 to 5 substituents (more preferably 1 or 2 substituents) on the phenyl moiety, which substituents are either halo groups, substituted or unsubstituted methyl or ethyl groups, or substituted or unsubstituted methoxy or 2-ethoxy groups. More preferably, R4 comprises 1 to 3 methyl, fluoro, chloro, bromo or methoxy groups, or any combination of these groups on either the alkylene or phenyl moiety.
The use of the particular ammonium ions in which all of R1-R3 are 2-hydroxyethyl groups may result in less odor during imaging the heat-sensitive polymer.
Particularly useful heat-sensitive polymers of these invention are described below as Polymers 2-14 and 16.
The heat-sensitive polymers may be readily prepared using many methods that will be obvious to one skilled in the art. Many carboxylic acid or anhydride-containing polymers are commercially available. Substituted benzyltrialkylammonium salts can be readily synthesized using preparative techniques that would be obvious to one skilled in the art. One convenient method involves the reaction of a substituted benzylamine with a desired alkyl halide, alkyl sulfonate ester or other alkyl-containing compound having a suitable xe2x80x9cleavingxe2x80x9d group. Another useful method involves the reaction of a substituted benzylic halide with a trialkylamine.
The carboxylic acid or anhydride-containing polymers can be converted to the desired quaternary ammonium carboxylate salts by a variety of methods including, but not necessarily limited to:
1) the reaction of a carboxylic acid or acid anhydride-containing polymer with the hydroxide salt of the desired quaternary ammonium ion,
2) the use of ion exchange resin containing the desired quaternary ammonium ion,
3) the addition of the desired ammonium ion to a solution of the carboxylic acid-containing polymer or a salt thereof followed by dialysis,
4) the addition of a volatile acid salt of the desired quaternary ammonium ion (such as an acetate or formate salt) to the carboxylic acid-containing polymer followed by evaporation of the volatile component upon drying,
5) electrochemical ion exchange techniques, and
6) the polymerization of monomers containing the desired quaternary ammonium carboxylate units.
Preferably, the first method is employed.
Although it is especially preferred that all of the carboxylic acid (or latent carboxylic acid) functionalities of the polymer are converted to the desired quaternary ammonium salt, imaging compositions in which the polymer is incompletely converted may still retain satisfactory imageability. Preferably, at least 50 monomer percent of the carboxylic acid (or equivalent anhydride) containing monomers are reacted to form the desired quaternary ammonium groups.
In the preferred embodiments of this invention, the heat-sensitive polymer is crosslinked. Crosslinking can be provided in a number of ways. There are numerous monomers and methods for crosslinking that are familiar to one skilled in the art. Some representative crosslinking strategies include, but are not necessarily limited to:
1) the reaction of Lewis basic units (such as carboxylic acid, carboxylate, amine and thiol units within the polymer with a multifunctional epoxide-containing crosslinker or resin,
2) the reaction of epoxide units within the polymer with multifunctional amines, carboxylic acids, or other multifunctional Lewis basic unit,
3) the irradiative or radical-initiated crosslinking of double bond-containing units such as acrylates, methacrylates, cinnamates, or vinyl groups,
4) the reaction of multivalent metal salts with ligating groups within the polymer (the reaction of zinc salts with carboxylic acid-containing polymers is an example),
5) the use of crosslinkable monomers that react via the Knoevenagel condensation reaction, such as (2-acetoacetoxy)ethyl acrylate and methacrylate,
6) the reaction of amine, thiol, or carboxylic acid groups with a divinyl compound (such as bis(vinylsulfonyl)methane) via a Michael addition reaction,
7) the reaction of carboxylic acid units with crosslinkers containing multiple aziridine or oxazoline units,
8) the reaction of acrylic acid units with a melamine resin,
9) the reaction of isocyanate crosslinkers with amines, thiols, or alcohols within the polymer,
10) mechanisms involving the formation of interchain sol-gel linkages [such as the use of the 3-(trimethylsilyl)propylmethacrylate monomer],
11) oxidative crosslinking using an added radical initiator (such as a peroxide or hydroperoxide),
12) autooxidative crosslinking, such as employed by alkyd resins,
13) sulfur vulcanization, and
14) processes involving ionizing radiation.
Ethylenically unsaturated polymerizable monomers having crosslinkable groups (or groups that can serve as attachment points for crosslinking additives) can be copolymerized with the other monomers as noted above. Such monomers include, but are not limited to, 3-(trimethylsilyl)propyl acrylate or methacrylate, cinnamoyl acrylate or methacrylate, N-methoxymethyl methacrylamide, N-aminopropylmethacrylamide hydrochloride, acrylic or methacrylic acid and hydroxyethyl methacrylate.
Preferably, crosslinking is provided by the addition of an epoxy-containing resin to the quaternary ammonium carboxylate polymer or by the reaction of a bisvinylsulfonyl compound with amine containing units (such as N-aminopropylmethacrylamide) within the polymer. Most preferably, CR-5L (an epoxide resin sold by Esprit Chemicals) is used for this purpose.
The imaging layer of the imaging member can include one or more of such homopolymers or copolymers, with or without up to 50 weight % (based on total dry weight of the layer) of additional binder or polymeric materials that will not adversely affect its imaging properties.
The amount of heat-sensitive polymer(s) used in the imaging layer is generally at least 0.1 g/m2, and preferably from about 0.1 to about 10 g/m2 (dry weight). This generally provides an average dry thickness of from about 0.1 to about 10 xcexcm.
The imaging layer can also include one or more conventional surfactants for coatability or other properties, dyes or colorants to allow visualization of the written image, or any other addenda commonly used in the lithographic art, as long as the concentrations are low enough so they are inert with respect to imaging or printing properties.
Preferably, the heat-sensitive imaging layer also includes one or more photothermal conversion materials to absorb appropriate radiation from an appropriate energy source (such as an IR laser), which radiation is converted into heat. Preferably, the radiation absorbed is in the infrared and near-infrared regions of the electromagnetic spectrum. Such materials can be dyes, pigments, evaporated pigments, semiconductor materials, alloys, metals, metal oxides, metal sulfides or combinations thereof, or a dichroic stack of materials that absorb radiation by virtue of their refractive index and thickness. Borides, carbides, nitrides, carbonitrides, bronze-structured oxides and oxides structurally related to the bronze family but lacking the WO2.9 component, are also useful.
One particularly useful pigment is carbon of some form (for example, carbon black). Carbon blacks which are surface-functionalized with solubilizing groups are well known in the art and these types of materials are preferred photothermal conversion materials for this invention. Carbon blacks which are grafted to hydrophilic, nonionic polymers, such as FX-GE-003 (manufactured by Nippon Shokubai), or which are surface-functionalized with anionic groups, such as CAB-O-JET(copyright) 200 or CAB-O-JET(copyright) 300 (manufactured by the Cabot Corporation) are especially preferred.
Useful absorbing dyes for near infrared diode laser beams are described, for example, in U.S. Pat. No. 4,973,572 (DeBoer), incorporated herein by reference. Particular dyes of interest are xe2x80x9cbroad bandxe2x80x9d dyes, that is those that absorb over a wide band of the spectrum. Mixtures of pigments, dyes, or both, can also be used. Particularly useful infrared radiation absorbing dyes include those illustrated as follows:
IR Dye 2 Same as Dye 1 but with chloride as the anion.
Useful oxonol compounds that are infrared radiation sensitive include Dye 5 noted above and others described in copending and commonly assigned U.S. Ser. No. 09/444,695, filed Nov. 22, 1999 by DoMinh et al.
The photothermal conversion material(s) are generally present in an amount sufficient to provide an optical density of at least 0.3 (preferably of at least 0.5 and more preferably of at least 1.0) at the operating wavelength of the imaging laser. The particular amount needed for this purpose would be readily apparent to one skilled in the art, depending upon the specific material used.
Alternatively, a photothermal conversion material can be included in a separate layer that is in thermal contact with the heat-sensitive imaging layer. Thus, during imaging, the action of the photothermal conversion material can be transferred to the heat-sensitive polymer layer without the material originally being in the same layer.
The heat-sensitive composition can be applied to the support using any suitable equipment and procedure, such as spin coating, knife coating, gravure coating, dip coating or extrusion hopper coating. The composition can also be applied by spraying onto a suitable support (such as an on-press printing cylinder) as described in U.S. Pat. No. 5,713,287 (noted above).
The imaging members of this invention can be of any useful form including, but not limited to, printing plates, printing cylinders, printing sleeves and printing tapes (including flexible printing webs). Preferably, the imaging members are printing plates.
Printing plates can be of any useful size and shape (for example, square or rectangular) having the requisite heat-sensitive imaging layer disposed on a suitable support. Printing cylinders and sleeves are known as rotary printing members having the support and heat-sensitive layer in a cylindrical form. Hollow or solid metal cores can be used as substrates for printing sleeves.
During use, the imaging member of this invention is exposed to a suitable source of energy that generates or provides heat, such as a focused laser beam or a thermoresistive head, in the foreground areas where ink is desired in the printed image, typically from digital information supplied to the imaging device. No additional heating, wet processing, or mechanical or solvent cleaning is needed before the printing operation. A laser used to expose the imaging member of this invention is preferably a diode laser, because of the reliability and low maintenance of diode laser systems, but other lasers such as gas or solid state lasers may also be used. The combination of power, intensity and exposure time for laser imaging would be readily apparent to one skilled in the art. Specifications for lasers that emit in the near-IR region, and suitable imaging configurations and devices are described in U.S. Pat. No. 5,339,737 (Lewis et al), incorporated herein by reference. The imaging member is typically sensitized so as to maximize responsiveness at the emitting wavelength of the laser. For dye sensitization, the dye is typically chosen such that its xcexmax closely approximates the wavelength of laser operation.
The imaging apparatus can operate on its own, functioning solely as a platesetter, or it can be incorporated directly into a lithographic printing press. In the latter case, printing may commence immediately after imaging, thereby reducing press set-up time considerably. The imaging apparatus can be configured as a flatbed recorder or as a drum recorder, with the imaging member mounted to the interior or exterior cylindrical surface of the drum.
In the drum configuration, the requisite relative motion between the imaging device (such as a laser beam) and the imaging member can be achieved by rotating the drum (and the imaging member mounted thereon) about its axis, and moving the imaging device parallel to the rotation axis, thereby scanning the imaging member circumferentially so the image xe2x80x9cgrowsxe2x80x9d in the axial direction. Alternatively, the thermal energy source can be moved parallel to the drum axis and, after each pass across the imaging member, increment angularly so that the image xe2x80x9cgrowsxe2x80x9d circumferentially. In both cases, after a complete scan by the laser beam, an image corresponding to the original document or picture can be applied to the surface of the imaging member.
In the flatbed configuration, the laser beam is drawn across either axis of the imaging member, and is indexed along the other axis after each pass. Obviously, the requisite relative motion can be produced by moving the imaging member rather than the laser beam.
While laser imaging is preferred in the practice of this invention, imaging can be provided by any other means that provides thermal energy in an imagewise fashion. For example, imaging can be accomplished using a thermoresistive head (thermal printing head) in what is known as xe2x80x9cthermal printingxe2x80x9d, described example in U.S. Pat. No. 5,488,025 (Martin et al). Thermal print heads are commercially available (for example, as Fujitsu Thermal Head FTP-040 MCS0001 and TDK Thermal Head F415 HH7-1089).
Without the need for any wet processing after imaging, printing can then ben carried out by applying a lithographic ink and fountain solution to the imaging member printing surface, and then transferring the ink to a suitable receiving material (such as cloth, paper, metal, glass or plastic) to provide a desired impression of the image thereon. If desired, an intermediate xe2x80x9cblanketxe2x80x9d roller can be used to transfer the ink from the imaging member to the receiving material. The imaging members can be cleaned between impressions, if desired, using conventional cleaning means.
The following examples illustrate the practice of the invention, and are not meant to limit it in any way.
Preparation of Useful Switchable Heat-sensitive Polymers
The polymers prepared as described below were characterized as having the ratio of moles of quaternary ammonium carboxylate groups to grams of polymer as shown in TABLE I below.
Preparation of Polymer 1 solution
An aqueous solution (60.00 g, 25% w/w) of polyacrylic acid (Polysciences, MWxcx9c90,000) was combined with distilled water (60 g) and 84.63 g of a 41.5% (w/w) methanolic solution of benzyltrimethylammonium hydroxide (Aldrich). A gummy precipitate initially formed and slowly redissolved over a half-hour. The resulting Polymer 1 was stored as a 32% (w/w) solution in water-methanol. Because this polymer is outside the scope of the present invention (no substituents on benzyl group), this polymer was used to make a Control printing plate.
Preparation of Solutions of Polymers 2-14
Polymers 2-14 were all synthesized using a basic three-step process. They are all within the scope of the present invention. The first step involved the reaction of the substituted benzyl halides with 1.5 to 3.0 equivalents of trimethylamine in ether to yield substituted benzyltrimethylammonium halide salts. These salts were characterized by proton NMR and electrospray-MS and the purity was further checked by reverse phase HPLC.
The second step involved the conversion of the halide salts to the corresponding hydroxides using 1.0 equivalents of Ag2O in methanol-water followed by the removal of volatiles to afford solutions with a hydroxide content of 0.5 to 2.5 mEq/g as determined by HCl titration. The hydroxide salts were characterized by electrospray-MS and the purity was checked by reverse phase HPLC.
The third step was the neutralization of polyacrylic acid (MW=90,000) with the various substituted benzyltrimethylammonium hydroxides to yield solutions (usually 20% w/w) of the polymers in MeOH/water (having weight ratios ranging from 2:1 to 1:2). A representative procedure is described below for making Polymer 2.
Preparation of Polymer 2 Solution (3 steps)
A] 3-Methylbenzyl bromide (24.64 g, 1.33xc3x9710xe2x88x921 mol, Aldrich) was dissolved in 221 g of diethyl ether in a 500 ml round bottomed flask. A 33% (w/w) solution of trimethylamine in methanol (35.80 g, 2.00xc3x9710xe2x88x921 mol, Acros) was added all at once, forming a white precipitate almost immediately. The reaction mixture was allowed to stir overnight at room temperature and was then filtered and washed three times with diethyl ether. The resulting white powder was dried in a vacuum oven overnight to afford 29.38 g (90% yield) of 3-methylbenzyl trimethylammonium bromide.
B] The bromide salt from step A (10 g) was dissolved in 100 ml of 9:1 methanol/water in a 250 ml round bottomed flask. Silver (I) oxide (9.5 g, 4.10xc3x9710xe2x88x921 mol, Aldrich) was added all at once and stirred for two hours at which point the silver oxide had changed color from a dark black to a dull gray. The solids were then filtered off, first using standard filter paper, then using a 0.5 xcexcm Millipore FC membrane filter. The filtrates were concentrated to a volume of xcx9c40 ml on a rotary evaporator. The concentration of hydroxide anion in the solution was determined to be 1.237. meq/g by HCl titration.
C] A 25% (w/w) aqueous solution (6.04 g) of polyacrylic acid (Polysciences, MW xcx9c90,000) was combined with 1.79 methanol and 17.17 g of the solution from step B. A gummy precipitate initially formed and slowly redissolved over a 30 minutes. The polymer was stored as a 20% (w/w) solution in methanol-water.
Polymers 3-14 were synthesized using analogous procedures. Variations from the representative procedure are noted where applicable in TABLE II below.
Preparation of Polymer 15 Solution (3 steps)
A] Benzyl tris(hydroxyethyl)ammonium bromide was synthesized from triethanolamine and benzyl bromide using the procedure of Rengan et al (J.Chem.Soc.Chem.Commun., 10, 1992, 757).
B] Benzyl tris(hydroxyethyl)ammonium bromide (26.78 g, 8.36xc3x9710xe2x88x922 mol) was dissolved in 250 ml of methanol and 5 ml water in a 500 ml round bottomed flask. Silver (I) oxide (20.56 g, 8.87xc3x9710xe2x88x922 mol) was added and the mixture was stirred at room temperature for 72 hours. The insoluble materials were filtered off and the filtrates were concentrated to 80 ml by rotary evaporation. The clear solution was passed through a flash chromatography column packed with 300 cm3 DOWEX(copyright) 550A OH resin using methanol eluent and concentrated to xcx9c50 ml by rotary evaporation. The concentration of hydroxide anion in the solution was determined to be 1.353. meq/g by HCl titration.
C] A 25% (w/w) aqueous solution (12 g) of polyacrylic acid (available from Polysciences, MW xcx9c90,000) was combined with 13.30 g of methanol and 30.75 g of the solution from step A. The resulting polymer was stored as a 25% (w/w) solution in a water/methanol mixture.
Preparation of Polymer 16 solution (3 steps)
A] 2-methylbenzyl bromide (10.00 g, 5.40xc3x9710xe2x88x922 mol, Aldrich), triethanolamine (10.48 g, 7.02xc3x9710xe2x88x922 mol, Aldrich), and tetrahydrofuran (54 ml) were combined in a 200 ml round bottomed flask fitted with a reflux condenser and a nitrogen inlet. The reaction was stirred at reflux for 14 hours at which point a large amount of a white solid had formed. The solid was collected by vacuum filtration, recrystallized from ethanol, and dried overnight in a vacuum oven at 60xc2x0 C. 10.67 g (59% yield) of a fine, white powder was collected.
B] 10.00 g (2.99xc3x9710xe2x88x922 mol) of the product from step A was converted to the corresponding hydroxide salt using the procedure described for Polymer 2 (step B). 30 ml of a solution with a hydroxide content of 0.906 mEq/g was obtained.
C] 3.38 g of a 25% (w/w) aqueous solution of polyacrylic acid (available from Polysciences, MW xcx9c90,000) was combined with 1.60 g of methanol and 15.02 g of the solution from step A. The resulting polymer was stored as a 20% (w/w) solution in a water/methanol mixture.

Imaging member containing heat switchable carboxylate polymer and method of use