A photosensitive flexographic printing element for the production of flexographic printing plates by digital imaging by means of lasers which has an IR-ablative layer with a polyether-polyurethane as binder. A process for the production of flexographic printing plates using an element of this type.

The present invention relates to a photosensitive flexographic printing element for the production of flexographic printing plates by digital imaging by means of lasers which has an IR-ablative layer comprising a polyether-polyurethane as binder. The invention furthermore relates to a process for the production of flexographic printing plates using an element of this type.
The conventional method for the production of flexographic printing plates by laying a photographic mask on a photopolymeric recording element, irradiating the recording element with actinic light through this mask and washing out the unpolymerized areas of the exposed element with a developer liquid is increasingly being replaced by CtP (computer-to-plate) technology, frequently also known as digital imaging. In CtP methods, the photographic mask in conventional systems is replaced by the masks integrated into the recording element.
Although a number of different methods have been proposed, only two have hitherto achieved significant importance in the market. In the first method, the photopolymerizable element is provided with a suitable ink receptor layer, and a mask is printed on by means of an ink-jet printer, as disclosed, for example, in WO 97/25206. The element can subsequently be exposed and developed in a known manner.
In the second method, the photopolymerizable element is coated with a substantially opaque, IR-ablative layer. Layers of this type usually comprise carbon black. Imagewise irradiation by means of a laser removes the IR-ablative layer at the points where it is hit by the laser beam, and the underlying photopolymerizable layer is uncovered. The image recording element can then be irradiated over its full area with actinic light through the ablatively formed mask in a known manner and washed out using a developer liquid. In the washing-out step, the nonablated residues of the IR-ablative layer and the underlying unpolymerized areas of the exposed element are removed.
Flexographic printing elements having IR-ablative layers are known in principle. EP-A 654 150 discloses a flexographic printing element having an IR-ablative layer. The IR-ablative layer comprises an IR-absorbent material. In addition, polymeric binders and a large number of different auxiliaries, for example dispersion aids or plasticizers, are disclosed as optional constituents. Furthermore, an additional barrier layer between the photopolymerizable layer and the IR-ablative layer is disclosed. This is intended to prevent diffusion of monomers from the photopolymerizable layer into the IR-ablative layer.
EP-A 741 330 discloses an IR-ablative flexographic printing element which has no barrier layer of this type. A multiplicity of widely differing polymers is disclosed as binders for the IR-ablative layer. Furthermore, the IR-ablative layer may also comprise a second binder in a smaller amount, for which a multiplicity of widely varying polymers is likewise disclosed.
EP-A 767 407 discloses a flexographic printing element having an IR-ablative layer which has an elastomeric, film-forming binder. Binders disclosed are polyamides and polyvinyl alcohol polyethylene glycol graft copolymers.
In the process for the production of flexographic printing plates by IR ablation, the quality of the IR-ablative layer is the crucial parameter for the quality of the flexographic printing plate and the economic efficiency of the process. The IR-ablative layer must satisfy a number of widely varying quality criteria:
It should have high sensitivity to lasers in order to ensure rapid and complete removal of the layer with the lowest possible laser power.
It should be soluble in conventional wash-out agents for the photopolymerizable layer so that it can be removed together with the unpolymerized constituents of the layer during the conventional development step. Otherwise, two wash-out steps would have to be carried out.
The laser apparatuses used nowadays are usually instruments with rotating drums (external or internal drums). The IR-ablative layer must therefore be elastic in order that it does not tear or wrinkle on clamping onto the drums.
It must be tack-free in order that no dust is attracted which could interfere with the IR ablation.
For storage and transport, flexographic printing elements are usually protected against damage by means of a protective film, which has to be removed before the IR ablation. The protective film must have only low adhesion to the IR-ablative layer in order that the IR-ablative layer is not damaged on removal.
Conversely, the IR-ablative layer must adhere strongly to the light-sensitive layer in order that it is not removed at the same time on removal of the protective film and in order that no air bubbles nullify the advantage of direct contact between the IR-ablative layer and the photopolymerizable layer.
The person skilled in the art who would like to produce a high-sensitivity, high-quality flexographic printing element having an IR-ablative layer sees himself confronted with a typical catch 22 situation. In order to obtain an IR-ablative layer with the highest possible sensitivity, the use of a self-oxidative binder, such as nitrocellulose, is advisable. However, nitrocellulose layers are very brittle, and consequently the elasticity of nitrocellulose layers is unsatisfactory and flexographic printing elements of this type wrinkle easily on clamping onto drum instruments. Although the brittleness can be reduced by addition of suitable plasticizers, the addition of plasticizers frequently has the consequence, however, of tacky layers with excessive cover film adhesion. However, typical tack-free binders, such as certain polyamides, have significantly lower sensitivity.
None of the cited documents from the prior art contains an indication of which components have to be selected from the multiplicity of possible components in order to obtain a flexographic printing element which meets all the outlined requirements.
It is an object of the present invention to provide a flexographic printing element having an IR-ablative layer which does not have the disadvantages of the prior art and satisfies the abovementioned requirements.
Accordingly, a photosensitive flexographic printing element for the production of flexographic printing plates by digital imaging by means of lasers has been found which comprises at least
a dimensionally stable support,
a photopolymerizable layer, at least comprising an elastomeric binder, a polymerizable compound and a photoinitiator or photoinitiator system,
a laser-ablatable layer having an optical density in the actinic spectral region of at least 2.5 and comprising at least one elastomeric binder and an IR absorber for laser radiation, and
optionally a removable, flexible protective film,
where the elastomeric binder of the IR-ablatable layer is an elastomeric polyether-polyurethane.
We have also found a process for the production of flexographic printing plates using an element of this type.
In detail, the following comments should be made regarding the invention.
In the photopolymerizable printing element according to the invention, a conventional photopolymerizable layer, if desired with an adhesion layer, is applied to a dimensionally stable support. Examples of suitably dimensionally stable supports are plates, films and conical and cylindrical tubes (sleeves) made from metals, such as steel or aluminum, or plastics, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN).
The photopolymerizable layer consists of a negative-working photopolymerizable mixture, i.e. one which is cured by exposure. This can be carried out by photocrosslinking with previously prepared polymers, by photopolymerization of low-molecular-weight, photopolymerizable compounds or both. Photopolymerizable layers essentially consist of a polymeric, elastomeric binder which can be washed out in the developer, an ethylenically unsaturated, free-radical-polymerizable compound, a photoinitiator or a photoinitiator system, and optionally further additives and auxiliaries. The composition of layers of this type is known in principle and is described, for example, in DE-A 24 56 439 or EP-A 084 851.
The elastomeric binder can be a single binder or a mixture of various binders. Examples of suitable binders are the known vinylaromatic-diene copolymers or block copolymers, for example conventional SIS or SBS block copolymers, diene-acrylonitrile copolymers, ethylene-propylene-diene copolymers or diene-acrylate-acrylic acid copolymers. Examples of suitable polymerizable compounds are conventional ethylenically unsaturated monomers, such as acrylates or methacrylates of mono- or polyfunctional alcohols, acrylamides or methacrylamides, vinyl ethers or vinyl esters. Examples include butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, butanediol di(meth)acrylate and hexanediol di(meth)acrylate. Suitable initiators for the photopolymerization are aromatic compounds, for example keto compounds, such as benzoin or benzoin derivatives.
The photopolymerizable mixtures may furthermore comprise conventional auxiliaries, for example inhibitors for thermally initiated polymerization, plasticizers, dyes, pigments, photochromic additives, antioxidants, antiozonants or extrusion aids.
The precise composition and thickness of the photopolymerizable layer is determined by the person skilled in the art depending on the particular requirements. It is also possible to employ a plurality of photopolymerizable layers of identical or different composition arranged one on top of the other. Furthermore, the element may comprise additional layers, for example adhesion layers, upper layers or elastic underlayers.
The photopolymerizable layers may be developable in aqueous or organic media, depending on the binder used. However, the advantages of the invention are particularly evident if the layer can be developed in organic media.
The element which is essential to the invention is the novel IR-ablative layer, which is applied to the photopolymerizable layer directly or also indirectly, i.e. separated by a thin interlayer, for example an adhesion or barrier layer. The IR-ablative layer is preferably applied directly to the photopolymerizable layer.
The IR-ablative layer comprises at least one elastomeric binder and an IR absorber for laser radiation and is essentially opaque to actinic radiation. In general, the optical density of the IR-ablative layer in the actinic spectral region is at least 2.5, preferably at least 3.0 and very particularly preferably at least 3.5. Said optical density is in each case measured at the wavelength or in the wavelength range employed for exposure of the element during the full-area irradiation.
The at least one elastomeric binder is a polyether-polyurethane. Suitable polyether-polyurethanes can be formed in a manner known in principle using difunctional polyethers which are capable of reaction with isocyanate groups, preferably polyether-diols. The difunctional polyethers are reacted with preferably symmetrical diisocyanates and short-chain, low-molecular-weight diols. This gives polymers which are built up from hard and soft segments and have elastomeric properties. Further details on the synthesis principle are given, for example, in xe2x80x9cPolyurethanes, Chapter 4.3; Ullmann""s Encyclopedia of Industrial Chemistry, Sixth Edition, 2000 Electronic Releasexe2x80x9d.
Suitable polyether-diols for the synthesis of the polyether-polyurethanes have the general formula HOxe2x80x94(Zxe2x80x94Oxe2x80x94)xH. These may be homopolymers comprising identical Z groups or copolymers or block copolymers having different Z groups in one molecule. The Z groups are, in particular, divalent radicals derived from ethylene, propylene or butylene. The polyether-diols can be obtained in a manner known in principle by polymerization of ethylene oxide, propylene oxide or butylene oxide using compounds which have active H atoms available, for example water or alcohols. They can also be prepared by polymerization of cyclic ethers, for example THF. It is also possible to employ polyether-diols additionally containing small amounts of further chain units. Examples which may be mentioned are carbonate groups obtainable by reaction of polyalkylene oxides with phosgene. However, the amount of additional units of this type should generally not exceed 5 mol %, based on the total amount of chain units. Polyether-polyurethanes are commercially available.
The mean molecular weight Mw (weight average) of the polyether-polyurethanes employed is usually from 20,000 to 200,000 g/mol, preferably from 20,000 to 150,000 g/mol and particularly preferably from 30,000 to 130,000 g/mol.
It is of course also possible to employ mixtures of two or more different polyether-polyurethanes.
The amount of polyether-polyurethanes in the IR-ablative layer is generally from greater than 40% by weight to a maximum of 90% by weight, based on the amount of all constituents of the IR-ablative layer, preferably from 45 to 80% by weight and very particularly preferably from 45 to 70% by weight.
The IR-ablative layer furthermore comprises a substance finely dispersed in the layer as absorber for laser radiation. This should have the highest possible absorption between 750 and 20,000 nm. Suitable substances as absorber include IR-absorbent dyes, for example phthalocyanines and phthalocyanine derivatives, merocyanines or methine dyes, and strongly colored inorganic pigments, for example carbon black, graphite, iron oxides or chromium oxides. Preference is given to carbon black. Besides the function as IR absorber, carbon black equally ensures that the IR-ablative layer is opaque to actinic radiation, meaning that it is not absolutely necessary additionally to employ a UV-absorbent dye. It is preferred to employ finely divided particles in order to obtain the highest possible tinting strength and the most uniform layer possible. Preference is given to finely divided carbon black grades, for example Printex(copyright) U, Printex(copyright) L6, Special Black 4 or Special Black 250 from Degussa.
The amount of absorber for the laser radiation is usually from 1 to 59.9% by weight, based on the sum of all constituents of the layer, preferably from 10 to 50% by weight and particularly preferably from 25 to 50% by weight.
The IR-ablative layer may additionally also comprise additional auxiliaries or additives. Examples of auxiliaries of this type are dispersion aids for pigments, fillers, plasticizers or coating aids. Auxiliaries or additives of this type are selected by the person skilled in the art depending on the desired properties of the layer, provided that they do not adversely affect the properties of the layer. Suitable dispersion aids for carbon blacks are, in particular, polyoxyalkylene derivatives, for example Solperse grades (Zeneca) or block copolymers, such as Disperbyk grades (Byk). It is also possible to employ UV absorbers as auxiliaries. This is usually not absolutely necessary in the case of the use of carbon black as absorber, but may occasionally be advantageous. On use of IR dyes as absorber, the use of additional UV absorbers is frequently unavoidable, although not absolutely necessary in each case. In general, the amount of all additives and auxiliaries should not exceed 20% by weight, preferably 10% by weight and very particularly preferably 5% by weight, based on the sum of all constituents of the IR-ablative layer.
All constituents of the IR-ablative layer should furthermore be selected in such a way that the IR-ablative layer is completely soluble or at least swellable in conventional organic developers for flexographic printing plates, so that the residues of the IR-ablative layer can be removed in a single operation together with the unpolymerized areas of the photopolymerizable layer. However, the invention is not restricted to this embodiment.
It is advisable to protect the IR-ablative flexographic printing element according to the invention against damage during transport, storage and handling by a flexible protective film, although a protective film of this type is not absolutely necessary.
The IR-ablative layer should be as thin as possible so that it can be removed as efficiently as possible by means of laser radiation. The thickness of the layer only has a lower limit insofar as the layer must have an optical density of at least 2.5. In general, a thickness of from 1 to 10 xcexcm is appropriate, without the invention thus being limited to this range.
In a particularly advantageous embodiment, the IR-ablative layer, besides the polyether-polyurethane or the polyether-polyurethanes, comprises at least one further binder of a different chemical nature, which will be referred to below as the secondary binder. It is also possible to employ a plurality of different binders as secondary binder. The amount of the secondary binder is less than the amount of the principal binder polyether-polyurethane. The amount of a secondary binder of this type is usually from 0 to 40% by weight, preferably from 0 to 20% by weight and particularly preferably from 0 to 10% by weight, based on all constituents of the IR-ablative layer.
The secondary binder is selected by the person skilled in the art depending on the desired properties of the IR-ablative layer, provided that the properties of the layer are not aversely affected by the secondary binder.
Besides the polyether-polyurethane, particularly proven secondary binders are cellulose derivatives which can be obtained, for example, by esterification or etherification of cellulose. Examples of suitable cellulose derivatives include methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, cellulose acetate, cellulose acetylpropionate, cellulose acetylbutyrate, nitrocellulose or mixtures thereof. Both nitrocellulose and ethylcellulose have proven very particularly successful.
The photosensitive flexographic printing elements according to the invention can be produced by firstly applying the photopolymerizable layer and optionally further layers to the support, and subsequently applying the IR-ablative layer, for example by casting or lamination. To this end, firstly all constituents of the layer are dissolved or dispersed in a suitable solvent or solvent mixture with vigorous mixing. A solution or dispersion of this type can be applied directly to the photopolymerizable element and the solvent evaporated. However, the solution can also be cast onto a support film, for example a PET film, and the solvent evaporated. The coated support is then laminated onto the photopolymerizable layer under pressure and/or the influence of heat. The support for the IR-ablative layer then functions as protective film for the entire photopolymerizable printing element.
The photosensitive printing elements according to the invention with an IR-ablative layer are employed for the production of flexographic printing plates. If present, the protective film is firstly removed. The IR-ablative layer is then irradiated imagewise using a suitable laser in order to obtain a photographic mask. Examples of suitable IR lasers include Nd/YAG lasers (1064 nm) and diode lasers (for example 830 nm). Suitable laser systems for computer-to-plate technology are commercially available, for example the OmniSetter(copyright) diode laser system (Misomex, wavelength 830 nm; working width 1800 mm) or the digilas(copyright) Nd/YAG laser system (Schepers), each of which comprises a cylindrical drum, onto which the flexographic printing element with IR-ablative layer is mounted. The drum is subsequently set in rotation, and the element is imaged by means of the laser beam.
After writing the mask, the photosensitive element is exposed over the entire area to actinic light through the mask. This can advantageously be carried out directly on the laser cylinder. However, the plate can also be taken off and exposed in a conventional flat-bed exposure apparatusxe2x80x94in air, under nitrogen or in vacuo. During the exposure step, the layer is photochemically crosslinked in the areas uncovered by IR ablation in the preceding process step, while the areas still covered remain uncrosslinked.
In a further process step, the exposed element is developed. The development can in principle be carried out in commercially available developer apparatuses using commercially available organic wash-out agents for flexographic printing plates, for example nylosolv(copyright) or Optisol(copyright). During the development, the unexposed areas of the photopolymerizable layer and the residues of the IR-ablative layer are removed. It is preferred to employ only a single wash-out agent for this process step. However, it is also possible firstly to remove the residues of the IR-ablative layer using a wash-out agent and subsequently to develop the plate in a second wash-out agent. After the development, the resultant flexographic printing plates are dried in a known manner. The process may comprise further process steps, for example detackifying with UV-C or Br2.
The flexographic printing elements according to the invention with an IR-ablative layer have a number of advantages:
Although the sensitivity to laser radiation does not reach that of pure nitrocellulose layers, it is nevertheless higher than that of most commercially available plates. The layer surface is tack-free and the protective or cover film adhesion is low, enabling the protective film to be removed without problems. On the other hand, the adhesion to the photopolymerizable layer is sufficiently great so that the IR-ablative layer remains adhering to the photopolymerizable layer even on rapid and unintentional removal of the protective film. The layers can be washed off using conventional organic wash-out agents, such as nylosolv(copyright) The surprisingly high elasticity is particularly advantageous, enabling flexographic printing plates of this type to be laid around the drums of laser exposure units without problems, without the layer tearing or wrinkling.
The following examples are intended to explain the invention by way of example.
General procedure for the preparation of a dispersion of IR absorber and binder
The dispersion aid (Solsperse 20 000) is pre-dissolved in the solvent mixture. The binder(s) and any further additives are subsequently added and dissolved with stirring. The carbon black is then added slowly and dispersed in for 15 minutes at a dissolver speed of 5000 rpm. The resultant mixture is ground for 1 hour in a laboratory stirred ball mill. The dispersion has a solids content of 10% by weight, based on the sum of all constituents.
The dispersion is coated onto a PET film using a laboratory knife coater and dried at 60xc2x0 C. for 10 minutes. The application rate is set so that a dry film with a thickness of about 2.5 xcexcm is formed. The optical density of a film of this type in the spectral region of actinic light is from 3.0 to 3.5.
The protective film and substrate layer are removed from a commercial flexographic printing plate of the FAH 254 type (BASF), so that the surface of the photopolymerizable layer is uncovered. The film coated with the IR-ablative layer is dry-laminated onto the surface of the photopolymerizable layer so that the IR-ablative layer and the photopolymerizable layer are bonded to one another. The PET film forms the protective film. The plate is stored for 1 week at room temperature.

Photosensitive flexographic printing element having an IR-ablative layer comprising polyether-polyurethanes


A non-ozone depleting, non-flammable co-solvent composition useful as a carrier for actives such as accelerators, catalysts, initiators, activators and other primer materials for use as adhesive promoter compositions in combination with adhesive compositions. The co-solvent compositions include an azeotropic, non-flammable solution of a fluorinated compound and a substituted benzene compound.

This invention relates to a non-ozone depleting, non-flammable co-solvent composition useful as a carrier for actives such as accelerators, activators, catalysts or other primer materials for use in combination with adhesive compositions. More particularly, the present invention relates to a co-solvent composition comprising a solution of a fluorinated compound and a substituted benzene compound.
Chlorinated hydrocarbons such as 1,1,1-trichloroethane, other chlorinated solvents and chlorfluoro hydrocarbons (CFC""s), such as C2F3Cl3, also known commercially under the trademark FREON(copyright), have been used for many years as solvents in numerous applications. These materials have shown to be very useful in the preparation of and as carriers for primer, activator, catalyst and accelerator compositions used in the adhesive field. These accelerators compositions often contain compounds, such as amine-bearing compounds, which require a solvent carrier for proper transport to and penetration of the substrate surface. Additionally, solvents are used to dilute the pure active compound to a useful concentration, usually on the order of about 0.01 to about 2% by weight.
In recent years, the use of chlorinated hydrocarbons, other chlorinated solvents and CFC""s has been substantially lessened due to their deleterious effect on the environment. Regulations have been promulgated not only in the United States but in countries throughout the world to accelerate the phase-out of environmentally destructive solvents, and in particular those which are believed to be ozone-depleting substances. In addition to laws designed to prevent the use of these substances, product labeling requirements have also been promulgated to insure notice is given as to those compounds used as alternatives. Finding acceptable alternatives, however, has been an extremely difficult task. For example, in applications such as adhesive accelerator compositions, the solvent must possess high chemical stability, non-flammability, low toxicity, and have a low volatile organic solvent (VOC) content, yet be sufficiently volatile to readily evaporate once applied, depositing the active ingredient, e.g. an amine accelerator, on a substrate. In addition to these requirements, consideration must be given to cost factors which are important for commercial feasibility.
Attempts to find good solvent systems which balance non-ozone depleting and non-flammable characteristics with sufficient volatility to be useful in adhesive applications, have not been entirely successful. Although many materials possess the ability to act as volatile solvents, most have been too flammable or toxic to serve as suitable replacements for conventional ozone-depleting compounds, i.e. chlorinated hydrocarbons or CFC""s. For example, materials such as heptane, acetone, methylethyl ketone, isopropanol, and methanol are excellent solvent systems, with good volatility, i.e. low flash point temperatures and high vapor pressures, but are extremely flammable. Other substances such as isoparaffins, and propylene glycol ether are less flammable, but do not exhibit adequate solvent performance properties for use in primer or accelerator compositions for adhesive systems.
One particular class of non-ozone depleting substances, which have been used in non-aqueous cleaning applications, are perfluorocarbons (PFC""s). These materials are essentially non-toxic, non-flammable and thermally and hydrolitically stable alternatives to CFC""s. In fact, the U.S. Environmental Protection Agency (EPA) has exempted PFC""s from their VOC list, which indicates that they are non-ozone depleting and essentially non-reactive and non-polluting in the vapor phase. PFC""s do, however, have the drawback of having low solvency for polar materials and most hydrocarbons. Thus, perfluorocarbons would not in themselves be expected to be useful as carriers for materials which require a solvent carrier, such as adhesion promoter compositions.
It is apparent, therefore, that a need exists for a solvent system which can carry actives, such as accelerator, activator, initiator, catalyst or primer compounds for adhesives, and which possess the following characteristics: non-ozone depleting, non-flammable, little or no VOC yet sufficient volatility for use as a carrier for active ingredients, low in toxicity and affordable in cost. The present invention is directed to overcoming the solvency deficiencies of perfluorocarbons, as well as addressing the aforementioned requirements for a useful alternative to CFC""s.
The present invention is directed to non-ozone depleting and non-flammable solvent composition which include a solution of a fluorinated first component selected from the group consisting of perfluorocarbons, dihydropolyfluoroalkanes having from 5 to 7 carbons and mixtures thereof; and a substituted benzene second component selected from the group consisting of parachlorobenzotrifluoride, monochlorotoluene, 3,4-dichlorobenzo-trifluoride, perchloroethylene, alpha, alpha, alpha-trifluorotoluene and mixtures thereof.
It has been discovered that the aforementioned fluorinated first component when combined with the substituted benzene second component results in a co-solvent composition which has the above-desired characteristics necessary to serve as replacements for CFC""s in adhesive promoter compositions. For purposes of the present invention, the term xe2x80x9cpromoterxe2x80x9d will be used to include accelerator, activator, initiator, catalyst or adhesion enhancing compounds, as well as other compounds used for initiating, accelerating or otherwise enhancing the polymerization of adhesive compositions.
Examples of materials useful with the co-solvent composition are active materials including tridodecylamine, 1,8-diazobicycloundecene, trihexadecylamine, hexamethyldisilazane, N-tert-butyl-2-benzothiazidesulfenamide, amine/BF3 complexes, dimethylparatoluene, N,N-diethyle-p-toluidene, triethylamine, tributylamine, aniline, benzylamine, triethylenetetramine, hydroxyethyldimethylamine, methylene-bis-4,4xe2x80x2-(N,N-dimethyl-o-toluidine) and combinations thereof.
The inventive co-solvent compositions are non-ozone depleting, non-flammable solvent systems which serve as excellent carriers for the aforementioned promoter components. Thus, for example, an amine accelerator for cyanoacrylate adhesives, may be added to the co-solvent composition to form an accelerator composition. Other promoter compositions for various adhesive systems, such as anaerobic adhesives, olefinic adhesives, epoxy adhesives, and acrylic adhesives, among others, may be formed from the present co-solvent compositions. Such promoter compositions are formed by adding the promoter component to the co-solvent composition in an appropriate amount such that when applied to a substrate surface, sufficient promoter component will be deposited to serve its intended function. The co-solvent compositions of the present invention are azeotropic which correlates with their non-flammable volatility.
The respective amounts of the two co-solvent materials may vary and is only limited by respective amounts which will no longer effectively dissolve actives. In general, the co-solvent compositions include the fluorinated first component to be present in amounts of about 60% to about 93% by weight, preferably about 70% to 80% of the composition, and most preferably about 75% to about 78%. The substituted benzene second component may be present in amounts of about 7% to about 40% by weight, and preferably about 10% to about 25% and most preferably, about 15% to about 20% of the co-solvent composition.
These co-solvent solutions can be used as carriers or hosts for a variety of active ingredients and guest materials which are dispersible or dissolvable therein. In preferred applications, the active material is an accelerator compound, such as an amine-containing compound, useful for accelerating the cure speed of adhesive compositions, and in particular, cyanoacrylate adhesives. In addition to such an accelerator compound, other materials can be incorporated into the co-solvent solution such as adhesion promoters, stabilizers, viscosity modifiers, odor masking agents, coloring agents, plasticizers and the like, and mixtures of these materials.
In a further aspect, the present invention includes a method of preparing an adhesive promoter composition, which includes the steps of forming a co-solvent composition of fluorinated first component and a substituted benzene second component, both as defined herein and which is liquid at room temperature and adding to said co-solvent composition a material which promotes the cure and/or enhances the adhesion of an adhesive.
The present invention further provides a method of bonding a non-polar substrate to another substrate, which may be polar or non-polar, which method comprises treating the non-polar substrate with an adhesive promoter composition which includes a co-solvent composition comprising the aforementioned fluorinated first component, the aforementioned substituted benzene second component and an adhesive promoter component.
The non-ozone depleting and non-flammable co-solvent compositions of the present invention include a solution of a fluorinated first component selected from the group consisting of perfluorocarbons, dihydropolyfluoroalkanes having from 5 to 7 carbons, trihydropolyfluoroalkanes having from 5 to 7 carbons and mixtures thereof; and a substituted benzene second component selected from the group consisting of parachlorobenzotrifluoride, monochlorotoluene, 3,4-dichlorobenzo-trifluoride, perchloroethylene, alpha, alpha, alpha-trifluorotoluene and mixtures thereof.
In a typical perfluorocarbon compound, fluorine atoms replace all of the carbon-bound hydrogen atoms on the hydrocarbon parent molecule. The strength of the carbon-fluorine bond allows for a high degree of thermal and chemical stability, resulting in low toxicity and low solvency for polar molecules and most hydrocarbons. For a discussion of these properties, see Grenfell, et al., xe2x80x9cPerformance Fluids For Critical Cleaning and Drying Applicationsxe2x80x9d, presented at the National Electronic Packaging and Production Conference. Thus, while their poor solvency for polar molecules and hydrocarbons makes them good choices for use on plastics, they have not been useful as solvents for adhesive promoter compounds. In fact, due to their inertness, few compounds have been known to dissolve in them. However, it has been discovered that the addition of the substituted benzene compounds disclosed herein to the perfluorocarbon greatly improves perfluorocarbon solubility, and results in a newly formed co-solvent composition. This composition can then be used as a carrier for a variety of active ingredients or guest materials. As previously mentioned, perfluorinated compounds have been found to be useful as cleaning fluids for fluorinated greases. Grenfell, et al. attributes this usefulness to the increase in perfluorocarbon solvency capability when azeotropic combinations are formed with specific hydrocarbons. For example, Grenfell, et al. discloses azeotropic mixtures of perfluoro-N-ethyl morpholine (90%) and 2,2,4 trimethylpentane (10%); and azeotropic mixtures of C6F14 (90%) and t-amylmethyether. These mixtures were found to have improved solvency and subsequently improved cleaning ability. These hydrocarbons, however, would not be useful in the present invention due to their flammability and incompatibility with various substrates
In addition to the perfluorocarbons, certain dihydro- and trihydropolyfluoroalkanes have also been found to be useful. These compounds have from 5 to 7 carbons and their preparation is described in U.S. Pat. No. 5,171,902. Examples of these compounds include CF3CHFCHFCF2CF3, CF3CH2CHFCF2CF3, CF3CHFCH2CF2CF3, CF3CHFCHFCF2CF2CF3, CF3CH2CHFCF2CF2CF3, CF3CHFCH2CF2CF2CF3, CF3CF2CH2, CHFCF2CF3, CF3CF2CHFCHFCF2CF2CF3, CF3CHFCHFCF2CF2CF2CF3, CF3CHFCH2CF2CF2CF2CF3, CF3CH2CHFCF2CF2CF2CF3, CF3CF2CHFCH2CF2CF2CF3, and CF3CF2CH2CHFCF2CF2CF3. The preferred compound is 2,3-dihydrodecafluoropentane.
It has been surprisingly discovered that the above-mentioned fluorinated first components can be combined with the aforementioned substituted benzene second component to form azeotropic solutions which are useful as co-solvent carrier compositions for adhesive promoter components. These combinations due to their azeotropic characteristics, have substantially identical vapor and liquid state makeup at their boiling points, thereby acting as a simple substance. The formation of an azeotrope is important to the low flash-point and non-flammability properties necessary for commercial acceptability. For purposes of the present invention the term xe2x80x9cnon-flammablexe2x80x9d will mean a flash-point of greater than about 200xc2x0 F. (94xc2x0 C.), whereby heating is required for the material to catch fire; and the term xe2x80x9cflammablexe2x80x9d will mean the material is ignitable with a spark rather than by heating, and having a flash point of less than about 100xc2x0 F. (38xc2x0 C.). Those compounds which have a flashpoint between 140-200xc2x0 F. are classified as combustible. These definitions are believed to be in accordance with those set by the U.S. Department of Transportation (DOT).
As previously mentioned, the components of the present invention are non-flammable and non-combustible within the definition given above. This is in contrast to other materials, such as isoparaffins or propylene glycol ether, which have been proposed as CFC replacements. These conventional solvent materials, while possessing good solvency and volatility properties, are combustible at temperatures below about 200xc2x0 F. (94xc2x0 C.). Other materials which exhibit excellent solvency properties, such as heptane, acetone, methylethyl ketone, methanol, propanol and the like, are highly flammable, requiring only a spark for ignition.
Thus, the present invention balances the properties of good solvency, non-flammability and non-combustibility, without being ozone-depleting. The co-solvent compositions of the present invention can serve as carriers for a variety of materials. Additionally, the present compositions are sufficiently volatile to serve as excellent carriers or solvents for adhesive promoter compositions, and in particular, amine-containing accelerator compositions. This is due to their ability to dissolve basic compounds such as amines and the like, deposit them onto a substrate surface, and quickly evaporate or flash-off, leaving behind the promoter compounds for reaction with a subsequently applied adhesive composition. The azeotropic vapor composition is non-flammable, non-combustible, non-ozone depleting, and non-toxic.
The particular promoter component used will depend for the most part on the adhesive composition to be employed as well as the type of substrate to be bonded. For example, cyanoacrylates, anaerobics, acrylics, epoxies and olefins each have classes of compounds which activate, accelerate or otherwise promote their cure and/or enhance adhesion.
The co-solvent compositions of the present invention have been found to be particularly useful with accelerator compounds for cyanoacrylate adhesive compositions. Cyanoacrylate adhesives are rapid setting materials which have excellent utility in bonding a variety of materials. The polymerization of cyanoacrylate adhesives is catalyzed using basic, i.e., anionic compounds, such as hydroxyl- or amine-containing compounds. In the present invention, the adhesive promoter may be selected from a wide variety of compounds capable of catalyzing or initiating the polymerization or enhancing the affinity for a substrate process. For example, among those compounds to be included are:
a) organic or inorganic substituted and unsubstituted amines such as primary, secondary and tertiary amines and their salts;
b) N-substituted alkanoamines;
c) acylated N-substituted alkanoamines;
d) polyamines, such as diamines;
e) heterocyclic amines such as the diazabicyclo or triazabicyclo compounds disclosed in U.S. Pat. No. 4,869,772.
(f) tertiary ammonium carboxylate compounds disclosed in U.S. Pat. No. 5,066,743 and having the formula:
xe2x80x83wherein R1, R2, R3 and R4 may each vary independently of each other and may be selected from the group consisting of alkyl, alkenyl, alkynyl, alkylaryl and arylalkyl, and preferably wherein at least one of R1, R2 and R3 is a long chain alkyl moiety having 6-20 carbon atoms and R4 is selected from the group consisting of alkyl and alkenyl;
g) phosphazene compounds including ring or chain polymers containing alternating phosphorus and nitrogen atoms, such as disclosed in U.S. Pat. No. 4,496,686;
h) ethylenediamine compounds such as those disclosed in U.S. Pat. No. 5,314,562 and having the formula:
xe2x80x83wherein each R5, which may be the same or different, represents hydrogen, an alkyl, alkenyl or alkoxy group having 1 to 8 carbon atoms, an aryl group having 6 to 8 carbon atoms, a nitrogen-, silicon- or silicon-substituted group having 1 to 8 carbon atoms or a heterocyclic group having up to 8 carbon atoms which may be unsubstituted or substituted with hydroxy, ether oxygen or sulphur.
i) quaternary ammonium compounds useful as primers for improving the adhesion, as disclosed in U.S. Pat. No. 5,079,098, having the formula:
xe2x80x83wherein R1, R2, R3 and R4 may each vary independently of the others and are selected from the group consisting of alkyl, hydroxyalkyl, aryl, alkaryl, aralkyl and alkenyl, optionally substituted with heteroatoms; and Axe2x88x92 is an anion whose pKa value in deprotonation equilibrium reaction is greater than about 0.
The above-mentioned U.S. Pat. Nos. 4,869,772, 5,066,743, 5,079,098, 4,496,686 and 5,314,562 are herein incorporated by reference.
Other useful amines include those disclosed in U.S. Pat. No. 3,260,637, used as accelerators for cyanoacrylates.
BF3/amine salts have also been found to be useful as adhesive promoter compounds. These BF3/amine complexes may be formed prior to adding to the adhesive primer composition, or formed in situ in the adhesive primer composition. In the latter case, BF3 in etherate or acetic acid medium, is reacted with an amine.
Tertiary amine/BF3 salts are preferred. The addition of specific ratios of amine to BF3, e.g., 5:1, allows for control over fixture time and can prevent or minimize blooming. Blooming is a cosmetic nuisance which results when adhesive vapor vaporizes and polymerizes on the edge of the bondline. The BF3/amine salt may be employed in effective promotor amounts and when used as a promotor for cyanoacrylate adhesives are effective in amounts of about 0.01 to about 4.0% by weight.
Among the preferred class of amines are those selected from the group consisting of tridodecylamine (TDDA), 1,8-diazobicycloundecene (DBU), trihexadecylamine, hexamethyldisilazane, tertiary amine/BF3 complexes and mixtures thereof. The compounds have been found to be particularly useful in the present invention to form an activator composition for cyanoacrylate adhesive compositions, and the like.
The co-solvent compositions of the present invention can be used with a variety of adhesive systems and are compatible with metallic and non-metallic surfaces. Adhesive promoter systems formed from the co-solvent compositions can be used on numerous types of bonding surfaces, such as steel, plastic, glass and wood. The co-solvent carrier compositions of the present invention provide a more environmentally friendly alternative to conventional solvents and, due to their inertness are compatible with, i.e. do not attack, most engineering plastics. In addition to being non-ozone depleting and non-flammable, the co-solvent carrier compositions of the present invention are low in toxicity, fast drying, i.e. quick evaporating, and can be commercially produced in a cost effective manner.
As previously mentioned, the present co-solvent compositions are formed by co-dissolving at least one halogenated and preferably fluorinated first component, such as a perfluorocarbon selected from the group consisting of perfluoromethylmorpholine, perfluoroalkanes having from 5 to 8 carbon atoms, dihydro- or trihydropolyfluoroalkanes having from 5 to 7 carbons, with an aliphatic hydrocarbon second component.
In one preferred embodiment of the invention, the co-solvent composition includes a combination of: I) a fluorinated compound having the empirical formula C5F11NO, or C5H2F10 and ii) parachlorobenzotrifluoride. The fluorinated compound may be present in amounts of about 60 to about 93% by weight, preferably about 70 to about 80% and most preferably, about 75 to about 78% by weight. In general, the parachlorobenzotrifluoride may be present in amounts of about 7.0 to about 40% by weight, preferably about 10 to about 25% by weight, and most preferably about 15 to about 20% by weight. In general, the co-solvent composition is prepared by co-dissolving, for example, about 7.0 to about 40% by weight of the substituted benzene second component, i.e., parachlorobenzotrifluoride or 3,4-dichlorobenzotrifluoride and the like in the fluorinated first component.
Another embodiment of the invention discloses a non-ozone depleting, non-flammable delivery system wherein the co-solvent serves as a carrier for actives or guest materials which are dispersible or dissolvable therein to form a homogeneous mixture or solution. In preferred applications, the guest material is an amine-containing compound, useful for accelerating the cure speed for adhesive compositions.
Other conventional additives useful in adhesive promoter compositions may be incorporated into the co-solvent compositions. These include, without limitation, stabilizers, viscosity modifiers, odor masking agents, coloring agents, plasticizers, and mixtures thereof.
The co-solvent compositions of the present invention may be formed into adhesive promoter compositions by the addition of an adhesive promoter component. In such a case, the adhesive promoter composition would include the co-solvent composition, and an active such as an adhesive promoter component. The present invention, when combined with an adhesive promoter component and employed as an adhesive promoter composition is intended to be applied to the surface of a metallic or non-metallic surface to be bonded, followed by application of the adhesive thereover, and finally, pressing together of the surfaces. These compositions are generally termed primer compositions. Such compositions are most effective when the surface free-energy of the solvent is close to that of the substrate surface to be adhesively bonded.
The concentration of the promoter component in a particular adhesive promoter composition may be determined by the type of adhesive, particular substrate surface, the promoter selected and the desired function or result. Generally, the promoter component is present in the adhesive promoter composition in amounts which are effective to produce the required cure speed and tensile strength. For example, amounts of from about 0.01% to about 10% by weight of the adhesive promoter composition are useful, with preferred amounts being about 0.01 to about 2%, and most preferably, about 0.25 to about 0.60% by weight. It is preferred to apply the adhesive promoter composition at the lowest effective concentration to decrease cost and increase ease of application, as well as allow the accelerator to be close to the thickness of a monomolecular layer. Typically, one application of the adhesive promoter on one side of the substrate is sufficient, although in certain instances it may be advantageous to coat both substrates. Multiple coatings may be applied where larger bond gaps and thicker adhesive layers are used.
The adhesive promoter composition comprising the co-solvent composition and the promoter component may be applied to the substrate surface to be bonded with the cyanoacrylate, or other adhesive, in any manner that is satisfactory to effect the desired result, e.g., to initiate or accelerate cure or enhance substrate adhesion. For example, spraying, dipping, brushing, swabbing, wiping, roller coating, etc. of the adhesion promoter composition onto one or more of the substrate surfaces prior to application of the adhesive, is preferred.
The thickness of the adhesive promoter composition and adhesive layer may vary widely, depending on the character and composition of the substrate surfaces, the particular adhesive and accelerator to be employed, as well as the end use of the final bonded assembly. With any given set of parameters, acceptable and optimum thicknesses may be determined by tensile shear strength values for particular samples at various primer and adhesive layer thicknesses. The adhesive layer of about xe2x80x9c0xe2x80x9d to about 5 mils and as great as about 10 mils have been found to be generally satisfactory for many substrates.
The co-solvent compositions of the present invention can be safely applied to a large variety of polymeric substrates, including thermosets and thermoplastics. Examples of thermoplastic materials include, without limitation, polycarbonate (PC), polyphenylene ether alloy, polyphenylene sulfide, polyphenylene oxide, nylon, melamine, polyacetal, polycarbonate, polyesters such as polybutyleneterephthalate (PBT) and polyethyleneterephthalate (PET), acrylic, acrylonitrile butadiene styrene (ABS), cellulose acetate, ethylene vinyl acetate (EVA), ionomer, polyaryl ether, and polyolefins such as polyethlene, polypropylene, polybutylene and polyallomer, polymethylpentane, polystyrene, polysulfone, polyvinyl chloride (PVC), styrene acrylonitrile (SAN), and styrene butadiene; thermosets such as epoxides and phenolics, among others, are also useful. Polytetrafluoroethylene (PTFE) has also been successfully bonded to using co-solvent compositions of the present invention. Composites, such as epoxy glass substrates, may also be used in conjunction with the inventive adhesion promoter and co-solvent compositions.
Other substrates, such as wood, metal, rubber, leather, cloth, paper or ceramics, are of course contemplated, since the co-solvent compositions of the present invention may be customized for a particular application by incorporation of the desired accelerator component.
As previously mentioned, the co-solvent compositions of the present invention are especially useful as carriers for cyanoacrylate adhesive promoter compositions, particularly for enhanced adhesion. Suitable cyanoacrylate adhesives are represented by the general formula:
wherein R6 is alkyl, alkenyl, cycloalkyl, aryl, alkoxalkyl, aralkyl, haloalkyl or other suitable group. The lower alkyl alpha-cyanoacrylates are preferred. In particular, these include methyl, ethyl, n-propyl, n-butyl, isobutyl, isopropyl, allyl, cyclohexyl, methoxyethyl, methoxypropyl, cyclohexyl, n-pentyl, allyl, and ethoxyethyl cyanoacrylates.
If a structural or engineering adhesive is to be employed, such as an anaerobic, the co-solvent composition can contain an anaerobic accelerating component which interacts with an initiator present in the adhesive composition to speed the cure. Tertiary alkyl amines, rhodamine and organic hydrazides, alkoxy amines, as well as ferrocene compounds are conventionally used as anaerobic accelerators.
Acrylic adhesives are typically two part systems; the first part containing the monomer and initiator component; and the second part containing the accelerator or curative component, which in the context of the present invention would be carried in the co-solvent composition. Other two part systems, such as epoxy systems, may also employ the co-solvent compositions of the present invention for carrying the curing agent, e.g. amines, anhydrides and the like.

Non-ozone depleting co-solvent compositions

deceasedby Tehyi Liu legal representative


A novel enzymatic approach for analytical method development is disclosed. A process wherein enzymes replace commonly used reagents/chemicals in a method/procedure. This approach increases the speed of analysis, reduces the usage of reagents/solvents, decreases the quantities of wastes generated, reduces the overall cost of drug testing/analysis in pharmaceutical or other related industries. The approach can be used to assay or analyze an active/inactive ingredient present in a solid, liquid, or semi-solid dosage forms of a drug.

The present invention relates generally to a novel approach to quantify/measure/assay an active or inactive ingredient in a drug or a formulation either in solid, semi-solid, or liquid dosage forms. The approach described herein utilizes enzymes that would lead to many advantages when compared to current/conventional non-enzymatic analytical methods/procedures development. This invention also applies to various analytical methods used in related industries like biotechnology, bioprocesssing, and chemical industries.
Analytical method development is carried out on a daily basis in many industries including pharmaceutical industries. Methods or procedures are developed for assays, identification, or estimation of the quantity, purity, or contaminants of a component or components of a product. Drug analysis or assay of actives/inactives in a formulation is performed regularly in pharmaceutical industries. These methods are used to test the stability or the integrity of a finished product and the reasons for the analysis of drugs include: to estimate the uniformity of the drug preparation to establish or release a bulk manufactured product; to estimate the shelf life or stability of the product; to check the quantity of active/inactive remaining in a drug/formulation after a certain period of time. These testing or analysis are carried out on solid, semi-solid, and liquid dosage forms.
The methods, though routine, are performed by a trained group of analysts solely dedicated for this task. These approaches use reactive compounds, organic solvents, or water and some of the common steps of a procedure are physico-chemical in nature such as titration, extraction, chromatography, or in general separation techniques. Though this approach works well, certain features are not desirable. Therefore, there is a need to improve or completely eliminate these negative features. The drawbacks are: use of large quantities of solvents/reagents/water, sequence of numerous analytical steps in analysis, disposal of large quantities of solvents/reagents, a large lab space to work and for storage of chemicals, disposal fee for solvents, more analysts"" time or man-hours requirement, to name a few. Conventional drug/pharmaceutical formulation analyses have other negative features apart from the above mentioned. The requirement of additional steps in a method would lead to more analysts"" errors. This certainly would lead to an extra amount of man-hours, resources (chemicals, reagents, solvents, water), exposure to hazards, and more importantly other projects accumulate thus affecting the deadlines and economics of drug manufacture itself. This becomes more clear with a detailed description of examples for acetaminophen and aspirin, comparing prior art and the present invention. Some of the examples where present invention can be applicable include: naproxen, ibuprofen, docusate sodium, hydrocortisone, pseudoephedrine, etc. to name a few.
There are numerous biochemicals and chemicals in nature that can be produced naturally or synthetically which are also biodegradable. These degrade over a period of time with the help of non-biological environmental factors such as air, pn rain, and sun. Apart from these factors, microorganisms like bacteria and fungi, also play a major role in degrading or destroying many of these biochemicals or chemicals that are disposed of into the environment.
Microorganisms accomplish this task with the help of enzymes present in them. Enzymes are an integral part of a microorganism""s mechanism to act on a substance or a suitable substrate to degrade it for food or nutrition. The enzymes are either intracellular or extracellular to microorganisms. The substrate or a chemical in the environment can be degraded outside or inside of a microorganism. Enzymes are involved in either situations. Some of the examples of enzymes are amylases, lipases, oxidases, dehydrogenases, cerulases, and hydroxylases.
Enzymes are highly specific in their reactivities toward chemicals. They combine or react with chemicals using the sites present on them. Besides specificity, enzymes react very quickly in comparison to a reaction between any two chemicals. Enzymes are powerful biocatalysts and they can be used in much smaller quantities to get the same kind of reactivity that is obtained with non-enzymatic chemical compounds. Therefore, a small amount of enzyme is capable of reacting with large amounts of chemicals at a faster rate. In other words, high specific nature of enzymes help them in converting or reducing a reactant to a product quickly. Enzymes are also reusable and easily biodegradable. The reaction product can be monitored and measured with the help of the product""s absorbance. Usually, the concentration of the product formed is directly proportional to absorbance (a linear relationship) and can be quantified with a spectrophotometer or a calorimeter.
Enzymes are also used in the field of immunology, where qualitative and quantitative analyses are performed on biologically active substances such as blood, saliva, or urine. The present disclosure is primarily aimed at non-biologically active substances such as drugs, formulations, or chemicals that have to be quantitatively assayed in various industries.
The present invention eliminates or reduces to a great extent most of the above problems through the use of enzymes. This approach has many decisive advantages which include simplicity, accuracy, less time consuming, cheaper, and non or less polluting.
It is a primary object of the present invention to provide a novel approach to quantify or measure an active or inactive ingredient in a drug/formulation through an enzymatic route. It is a further object of the present invention that by following this approach one can realize many advantages over current analytical/method development procedures namely:
a) faster analysis
b) lower chemicals/reagents usage and cost
c) fewer man-hours
d) smaller lab space
e) fewer health/safety hazards
f) cheaper approach
g) less strain on the environment due to fewer pollutants
The examples given below illustrate the benefits of enzymatic approach. The cumbersome methods that are being followed can be replaced by a simpler, faster, cheaper method. Since the drug testing is routinely performed throughout the world, one or more positive features of enzymatic approach could save millions of dollars in disposal requirements, reagents cost, and total testing time. Saving testing time could also mean more testing of batches in a short amount of time and a faster release of products into the market at a lower price. A reduction in harmful and dangerous reagents and solvents usage would reduce the exposure amount for an analyst and enhances the working conditions in the laboratories.
Anyone skilled in the art of method development would appreciate the potential benefits of the enzymatic approach. The scope of the approach is not just limited to the analysis of a single active or inactive ingredient in one step, but unlimited to many active or inactive ingredients testing simultaneously with the help of one or more enzymes.
The method is also amenable to automation. Once the analytical method is validated the amount of chemicals required, man-hours saved, and the overall method ruggedness play vital roles in cutting down the cost of product or raw material testing. This means the overall product cost will decrease and in return the consumers can buy drugs/pharmaceuticals for a lower price. Further, the introduction of enzymatic approach can lead to exciting new avenues in the field of analytical method development. Some examples such as simultaneous testing of two or more ingredients, information on the interplay between enzyme-active-excipient, and the application of the latter in medicine and health, etc.
The following two examples describe the differences between the current or conventional approach in drug and pharmaceutical industries and the enzymatic approach of the present invention. First example describes the testing of a drug component acetaminophen and the second example illustrates the testing performed on aspirin, which is also a drug component. It is clear from both examples that the advantages of the present disclosure over the conventional approach are not only useful but essential in saving time, keeping the environment clean, and accelerating the drug testing process.

Enzymatic approach for analytical method development


The invention provides well drilling and servicing fluids comprising an alkaline aqueous liquid containing chitosan, an anhydride, and an aldehyde therein. The invention further provides a method of drilling a well wherein there is circulated in the wellbore during drilling a drilling fluid comprising an alkaline aqueous liquid containing chitosan and an anhydride, and optionally an aldehyde therein.

The invention pertains to the in-situ modification of chitosan to produce viscosifiers (thickeners, gellants) for aqueous liquids, and to viscosified aqueous well drilling and servicing fluids containing such modified chitosans dispersed therein, and to methods of drilling a well utilizing such fluids.
Many viscosifiers for, and methods of, increasing the viscosity of aqueous liquids are known. Such viscosifiers may be so-called water-soluble polymers such as biopolymers, gums, cellulose derivatives, alginates, and other polysaccharides or polysaccharide derivatives, and various synthetic polymers. Representative polymers are set forth in the book xe2x80x9cHandbook of Water Soluble Gums and Resins,xe2x80x9d Robert L. Davidson, Ed., 1980.
Noticeably absent from this book is any mention of chitosan or derivatives thereof.
Viscoelastic fluids are characterized as having a rheological profile which is shear thinning, having a high viscosity at extremely low shear rates and a low viscosity at high shear rates. Thus such fluids are pseudoplastic having a high yield stress.
This type of rheology is produced by hydrating in the fluid certain water soluble polymers. These polymers presently known are biopolymers, i.e., microbially produced polysaccharides or heteropolysaccharides, and are well known in the art.
There is a need for fluids which exhibit a high low shear rate viscosity which are shear thinning.
Chitosan is a partially or fully deacetylated form of chitin, a naturally occurring polysaccharide. Structurally, chitin is a polysaccharide consisting of beta-(1xe2x86x924)2-acetamido-2-deoxy-D-glucose units, some of which are deacetylated. The degree of deacetylation usually varies between 8 and 15 percent, but depends on the species from which the chitin is obtained, and the method used for isolation and purification.
Chitin is not one polymer with a fixed stoichiometry, but a class of polymers of N-acetylglucosamine with different crystal structures and degrees of deacetylation, and with fairly large variability from species to species. The polysaccharide obtained by more extensive deacetylation of chitin is chitosan.
Like chitin, chitosan is a generic term for a group of polymers of acetylglucosamine, but with a degree of deactylation of between 50 and 100 percent. Chitosan is the beta-(1-4)-polysaccharide of D-glucosanine, and is structurally similar to cellulose, except that the C-2 hydroxyl group in cellulose is substituted with a primary amine group in chitosan. The large number of free amine groups (pKa=6.3) makes chitosan a polymeric weak base. Both chitin and chitosan are insoluble in water, dilute aqueous bases, and most organic solvents. However, unlike chitin, chitosan is soluble in dilute aqueous acids, usually carboxylic acids, as the chitosonium salt. Solubility in dilute aqueous acid is therefore a simple way to distinguish chitin from chitosan.
Chitosan is unique in that it is a polysaccharide containing primary amine groups. Chitosan forms water-soluble salts with many organic and inorganic acids.
It is known to prepare chitosan derivatives by attaching various groups to one or more hydroxyl groups of the chitosan, as in various cellulose derivatives, and/or in attaching various groups to the primary amino group of chitosan. Thus it is disclosed in Hall and Yalpani U.S. Pat. No. 4,424,346 that chitosan can be reacted with various aldehydes by Schiff base formation with the primary amino group. The reaction is conducted in the presence of a reducing agent, specifically sodium cyanoborohydride, to reduce the imino group formed to a secondary amino group, i.e., the chitosan undergoes reductive alkylation. The aldehyde reactants include aldose or ketose sugars, or sugars oxidizable or hydrolyzable to aldoses or ketoses, for example, glucose, galactose, arabinose, xylose, N-acetylglucosamine, lactose, cellobiose, maltose, and melibiose, and aromatic aldehydes containing at least one hydroxyl or carboxyl group. Example 5 specifically discloses the reductive alkylation of chitosan with lactose at weight ratios of lactose/chitosan of 2.4 (Product A), 3.0 (Product B, Product C), and 6.0 (Product D), to form products having the groupxe2x80x94NHRxe2x80x2 therein, where Rxe2x80x2 is an aldose or ketose residue. When the reaction was carried out in the absence of the sodium cyanoborohydride reducing agent at a weight ratio of lactose/chitosan of 8.0, the resulting product was minimally reacted with a degree of substitution of only 0.1. The reactions were carried out at room temperature. A paper which discusses the preparation and characteristics of the chitosan derivatives set forth in the Hall et al. U.S. Pat. No. 4,424,346 is xe2x80x9cSome Chemical and Analytical Aspects of Polysaccharide Modifications. 3. Formation of Branched-Chain, Soluble Chitosan Derivatives,xe2x80x9d M. Yalpani and L. D. Hall, MACROMOLECULES 1984, 17, 272-281. These chitosan derivatives are disclosed to offer a wide range of solubility, gelling and compatibility properties.
A paper entitled xe2x80x9cChitosan Derivatives Bearing C10-Alkyl Glycoside Branches: A Temperature-Induced Gelling Polysaccharide,xe2x80x9d K. R. Holme and L. D. Hall, Macromolecules 1991, 24, 3828-3833, discloses chitosan derivatives having mixed hydrophobic/hydrophilic branches.
U.S. Pat. No. 3,879,376, incorporated herein by reference, discloses chitosan derivatives formed by acylation of chitosan with a saturated or unsaturated organic diacid anhydride and their use as a skin-moisturizing agent in cosmetic compositions.
The following papers disclose the reaction of chitosan with various anhydrides, each incorporated herein by reference: (1) xe2x80x9cFormation and Characterization of a Physical Chitin Gel,xe2x80x9d L. Vachoud et al., Carbohydrate Research 302 (1977), 169-177; (2) xe2x80x9cChitosan Film Acylation and Effects on Biodegradability,xe2x80x9d Jin Xu et al., Macromolecules 1996, 29, 3436-3440; (3) xe2x80x9cN-Acetylchitosan Gel: A Polyhydrate of Chitin,xe2x80x9d Shigehero Hirans et al., Biopolymers 15 (1976), 1685-1691.
There is disclosed in co-pending U.S. patent application Ser. No. 09/222,293 filed Dec. 28, 1998, well drilling fluids containing chitosan and aldose or ketose sugars, and/or oligosaccharides of such sugars.
We have now determined that aqueous alkaline fluids useful in oil and gas well operations, such as drilling, fracturing, sand control, lost circulation control, completion, workover and the like can be formulated to contain chitosan and an anhydride modifier. The chitosan and anhydride react to increase the viscosity of the fluid. Optionally, the fluids can contain an aldehyde modifier to increase the viscosity or enhance the stability of the fluids.
Thus, it is an object of the invention to provide aqueous alkaline well drilling and servicing fluids containing chitosan and an anhydride modifier.
It is another object of the invention to provide aqueous well drilling and servicing fluids containing chitosan, an anhydride modifier, and a modifier selected from the group consisting of an aldehyde, pyruvic acid, and mixtures thereof.
Another object of the invention is to provide a method of drilling a well comprising circulating in a wellbore during drilling an aqueous alkaline fluid containing chitosan and an anhydride modifier therefore.
Still another object of the invention is to provide a method of drilling a well comprising circulating in a wellbore during drilling an aqueous alkaline fluid containing chitosan, an anhydride modifier, and a modifier selected from the group consisting of an aldehyde, pyruvic acid, and mixtures thereof
Yet another object of the invention is to provide aqueous alkaline fluids useful in oil and gas well operations comprising an aqueous liquid having incorporated therein chitosan, an anhydride modifier, optionally an aldehyde modifier, optionally pyruvic acid, and an alkalizing additive.
These and other objects of this invention will be apparent to one skilled in the art upon reading this specification and the appended claims.
While the invention is susceptible of various modifications and alternative forms, specific embodiments thereof will hereinafter be described in detail and shown by way of example. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the invention is to cover all modifications and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.
The compositions can comprise, consist essentially of, or consist of the stated materials. The method can comprise, consist essentially of, or consist of the stated steps with the stated materials.
The invention provides oil and gas well drilling and servicing fluids containing chitosan which is modified in-situ with one or more anhydrides and, optionally, one or more aldehydes and/or pyruvic acid. The fluids are useful in various operations such as drilling, fracturing, sand control, lost circulation control, completion, workover, and the like. The preferred fluids are alkaline aqueous pseudoplastic fluids having a Brookfield 0.5 rpm viscosity (hereinafter sometimes referred to as xe2x80x9clow shear rate viscosityxe2x80x9d or xe2x80x9cLSRVxe2x80x9d) of at least 5,000 centipoise and a shear thinning index (hereinafter sometimes referred to as xe2x80x9cSTIxe2x80x9d) greater than about 10. The STI is the ratio of the Brookfield viscosity at 0.5 rpm to the Brookfield viscosity at 100 rpm and is an indication of the shear thinning, pseudoplastic characteristic of the fluids. Preferably the LSRV is at least about 10,000 centipoise, most preferably at least about 20,000 centipoise.
The chitosans useful in the fluids will have at least 50% of their amino groups deacetylated, i.e., the degree of deacetylation is at least 50%, preferably at least 70%, and most preferably from about 85% to 100%.
The concentration of chitosan in the fluids will be sufficient, when reacted in-situ with the anhydride(s) and aldehyde(s) and optional pyruvic acid, to impart to the fluids the rheological characteristics desired. Generally the concentration of chitosan will be from about 0.5 lb/bbl (0.143 % w/v) to about 5 lb/bbl (1.429% w/v), preferably from about 1 lb/bbl (0.286 % w/v) to about 4 lb/bbl (1.143 % w/v).
The fluids are initially preferably prepared by forming an acidic aqueous chitosan solution/dispersion containing the anhydride modifier, wherein the pH is from about 2 to about 6, preferably from about 3 to about 5.5, and thereafter raising the pH to basic, i.e., to a pH of about 7.5 or above, preferably from about 8 to about 11.
A wide variety of acids can be used to solublize chitosan. Such acids include inorganic acids such as hydrochloric acid, nitric acid, and sulfamic acid, and water soluble organic acids represented by the formula: Rxe2x80x94(COOH)n wherein n has a value of 1 to 3 and R represents a mono- or divalent organic radical composed of carbon, hydrogen, and optionally at least one of oxygen, nitrogen, and sulfur. Exemplary organic acids are the mono- and dicarboxylic acids such as formic, acetic, N-acetylglycine, acetylsalicylic, glycolic, lactic, malic, 2-pyrrolidone-5-carboxylic, salicylic, glutamic, glutaric, malonic, and thioglycolic acids.
The preferred acid used to prepare the acidic chitosan solution is selected from the group consisting of (a) monocarboxylic acids containing from one to three carbon atoms, (b) substituted monocarboxylic acids containing at least one radical per molecule selected from the group consisting of hydroxyl, amino, chloro, and thio, and containing from one to three carbon atoms, and (c) mixtures thereof.
The concentration of acid should be sufficient to decrease the pH of the solution to less than about 6.0, preferably 5.5 or less.
The basic compound used to raise the pH to the alkaline range can be any compatible base which can be determined by routine testing. Preferred basic compounds are the alkali metal and ammonium hydroxides, carbonates and bisulfites, and mixtures thereof. Organic bases such as low molecular weight amines and hydroxyamines, such as ethanolamine and the like, can be used to raise the pH, also in combination with an inorganic basic compound. Preferred bases are the alkali metal carbonates.
The water base borehole fluids and well servicing fluids of this invention generally will contain materials well known in the art to provide various characteristics of properties to the fluid. Thus the fluids may contain one or more viscosifiers or suspending agents in addition to the chitosan, weighting agents, corrosion inhibitors, soluble salts, biocides, fungicides, seepage loss control additives, bridging agents, deflocculants, lubricity additives, shale control additives, pH control additives, and other additives as desired.
The borehole fluids may contain one or more materials which function as encapsulating or fluid loss control additives to restrict the entry of liquid from the fluid to the contacted shale. Representative materials known in the art include partially solublized starch, gelatinized starch, starch derivatives, cellulose derivatives, humic acid salts (lignite salts), lignosulfonates, gums, biopolymers, synthetic water soluble polymers, and mixtures thereof.
The oil and gas well drilling and servicing fluids of this invention preferably have a pH in the range from about 7.5 to about 11.5, most preferably from 8 to about 11.
If desired, water soluble potassium compounds can be incorporated into the fluids of this invention to increase the potassium ion content thereof. Thus it is known to add potassium chloride, potassium formate, potassium acetate, and the like to fluids to enhance the shale stabilizing characteristics of the fluids.
The well drilling and servicing fluids of this invention contains an aqueous phase which may be fresh water, a natural brine, sea water or a formulated brine. The formulated brine is manufactured by dissolving one or more soluble salts in water, a natural brine, or sea water. Representative soluble salts are the chloride, bromide, acetate and formate salts of potassium, sodium, calcium, magnesium and zinc. The preferred salts contain a monovalent cation.
The borehole fluid of this invention is circulated or spotted within a borehole during well drilling or servicing operations as is well known in the art. Fracturing fluids are used to hydraulically fracture subterranean formations as is well known in the art.
The anhydride modifiers suitable for use in the present invention are saturated or unsaturated organic diacid anhydrides, substituted products of such anhydrides, and mixtures thereof, wherein the substituted products contain one or more functional groups selected from the group consisting of hydroxyl, carboxyl, alkenyl, amino, and mixtures thereof. Exemplary saturated anhydrides are succinic anhydride (preferred), acetoxysuccinic anhydride, methylsuccinic anhydride, diacetyl tartaric anhydride, tartaric anhydride, glutaric anhydride, glutamic anhydride, and the like. Exemplary unsaturated anhydrides used can be maleic anhydride (preferred), itaconic anhydride, citraconic anhydride, dodecenylsuccinic anhydrides, octadecenylsuccinic anhydride, other alkenyl succinic anhydrides, and the like wherein the alkenyl group contains from about 2 to about 20 carbon atoms, and mixtures thereof.
The concentration of anhydride in the fluid is from about 10% to about 250% of the weight of chitosan in the fluid, i.e., the weight ratio of anhydride to chitosan is from about 0.1 to 1 to about 2.5 to 1. It is preferred that the weight ratio of the succinic anhydride to chitosan is from about 0.1 to 1 to about 1.5 to 1.
Alkanoic acid anhydrides (alkanoic anhydrides) such as acetic anhydride, propionic anhydride, butyric anhydride, dodecanoic anhydride, and the like can be used together with the organic diacid anhydrides.
The fluids of the invention can also optionally contain one or more aldehydes to react with the chitosan and the acylated chitosan derivatives present in the fluids. Representative aldehydes include alkanals containing from 1 to 20 carbon atoms, substituted alkanals containing one or more functional groups selected from the group consisting of hydroxyl, carboxyl, amino, keto, aldehydo (xe2x80x94CHO), and mixtures thereof, benzaldehyde, substituted benzaldehydes wherein the benzene ring contains one or more functional groups selected from the group consisting of hydroxyl, carboxyl, and mixtures thereof, aldose or ketose sugars and oligosaccharides of the sugars containing up to about 10 sugar groups per molecule, and mixtures thereof Exemplary alkanals are formaldehyde, propional, butanal, dodecanal, and the like. Exemplary substituted alkanals contain such substituent groups as hydroxyl, carboxyl, amino, keto, xe2x80x94CHO, and the like, such as glyoxal, glutaraldehyde, glyceraldehyde, and pyruvaldehyde. Exemplary substituted benzaldehydes include salicylaldehyde, 4-carboxybenzaldehyde, 4-hydroxybenzaldehyde, vanillin, 3-formyl-2-hydroxybenzaldehyde, and the like. Representative sugars are selected from the group consisting of arabinose, galactose, glucose, mannose, xylose, and mixtures thereof. Oligosaccharides containing from about two to about ten combined sugar units from the above group may be present in the fluids of the invention.
A preferred oligosaccharide is lactose, a disaccharide containing one glucose sugar unit and one galactose sugar unit per molecule. Other suitable oligosaccharides include such disaccharides as dextrose, maltose, melibiose, and cellobiose.
A mixture of oligosaccharides (hereinafter sometimes referred to as xe2x80x9cOSMxe2x80x9d) useful in the present invention is obtained from the thermal hydrolysis of lignocellulose materials. The thermal hydrolysis may be carried out in any one of several manners such as by subjecting wood of trees and woody materials of corn stalks, cane, and other vegetable growths to the action of steam under elevated temperatures and pressures. The OSM may also be obtained by acid hydrolysis of lignocelluloses as well as by saccharification of wood. Preferably, however, the thermal hydrolysis is carried out by charging wood chips to a closed chamber (e.g., a gun as set forth in Mason U.S. Pat. No. 1,824,221, incorporated herein by reference), subjecting the chips to pressure of about 200-1200 pounds per square inch and a temperature of about 200-300xc2x0 C. for approximately 30 minutes to 5 seconds, respectively, in the presence of steam, and then discharging the woody material from the gun through a constricted discharge means therein into a zone of lower pressure, preferably atmospheric pressure, thereby exploding the wood chips into comparatively finely divided elongated fibers. Under this treatment the wood undergoes hydrolysis, and water-insoluble and readily hydrolyzable constituents thereof are rendered soluble or dispersible in water. These water solubles are removed from the fiber, which may be accomplished by washing the fiber in water or by squeezing the fiber with rolls and/or screws and the like apparatus. See for example Boehm U.S. Pat. No. 2,224,135, incorporated herein by reference. The water solubles can be concentrated or rendered solid by removing water therefrom, as by evaporation, drying, etc.
Water solubles resulting from such hydrolysis of lignocellulose materials as a class are applicable to this invention. A typical analysis of the water solubles, the OSM of this invention, made from pine wood is as follows: hexosans, 40% by weight; pentosans, 30% by weight; lignin, 15% by weight; non-sugar carbohydrates, 10% by weight; and gums, 5% by weight. The constituents of the OSM will vary somewhat depending on the type of lignocellulose material hydrolyzed and the conditions, e.g., time, temperature, pressure, etc. Depending upon these conditions, the constituents of the OSM can vary roughly as follows: pentosans and hexosans, 60-80% by weight; lignin, 5-25% by weight; non-sugar carbohydrates, 5-15% by weight; and gums, 2-8% by weight. From the above description it will be seen that the major proportion of the water solubles consists of carbohydrate material. A more detailed analysis of the water solubles has indicated that the carbohydrate mixture is composed of oligosaccharides consisting of mannose, arabinose, glucose, galactose, and xylose sugar units. The crude water solubles from which relatively all of the suspended material has been removed consists almost entirely of the above described oligosaccharide mixture. There is a relatively small fraction present, about up to about 15% thereof, of monosaccharides. A larger fraction of the dissolved solids, i.e., greater than about 50% thereof, consists of hexose and pentose oligosaccharides containing from 2 to 5 of the corresponding monosaccharide sugar units which are predominantly those named above. The remainder of the dissolved solids has been found to consist of oligosaccharides having more than about 6 sugar units of the same 5 and 6 carbon characters. In most instances, the filter water solubles contain only from about 3 to about 5% of lignin.
Other oligosaccharide mixtures useful in the practice of this invention include cane syrup solids, corn solubles, and the like.
Generally the concentration of the aldehyde will be from about 0.7 kg/m3 (0.25 ppb) to about 57 kg/m3 (20 ppb), preferably from about 0.7 kg/m3 (0.25 ppb) to about 43 kg/m3 (15 ppb).
As indicated hereinbefore, the fluids of this invention can contain pyruvic acid. Generally the concentration of pyruvic acid, if present, will be from 0.1 kg/m3 to about 2.85 kg/m3 (1 ppb).
Mixtures of chitosan and the anhydride, optionally with the optional aldehyde and optional pyruvic acid, can be prepared for addition to the alkaline fluids of this invention for maintenance of the properties thereof, or indeed, for preparing the initially prepared acidic oil and gas well drilling and servicing fluids before adding the alkalizing additive thereto. Preferably the mixture of chitosan and the anhydride are treated such that the chitosan and the anhydride are at least partially reacted prior to addition to the fluid.
As indicated hereinbefore, the fluids set forth herein are useful in drilling a well wherein there is circulated in a wellbore (borehole) a drilling fluid during the drilling thereof. Such processes are well known in the art. Generally, the method of drilling a well penetrating a subterranean formation comprises circulating an aqueous alkaline chitosan and anhydride-containing fluid as set forth herein through the well by introducing the drilling fluid into the well and into contact with the formation and withdrawing the drilling fluid from the well to remove cuttings therefrom. The fluids can be formulated for use as spotting fluids for use in releasing stuck pipe or tools within a borehole wherein the fluid is circulated to the depth in the borehole of the stuck pipe or tool and in a volume sufficient to displace the fluid in the borehole over the entire stuck area, and allowing the spotting fluid to soak for a period of time sufficient to release the stuck pipe or tool. The fluids can be formulated to provide viscous gels to overcome lost circulation problems in a wellbore as is known in the art.
In order to more completely describe the invention, the following non-limiting examples are given. In these examples and in this specification, the following abbreviations may be used: ml=milliliter; g=gram; cp=centipoise; ppb=pounds per 42 gallon barrel; OS=off-scale; PV=API plastic viscosity in centipoise; YP=API yield point in pounds per 100 square feet; rpm=revolutions per minute; API=American Petroleum Institute; LSRV=low shear rate viscosity in centipoise as determined with a Brookfield Viscometer at 0.5 rpm; STI=the shear thinning index obtained with a Brookfield Viscometer, which is the ratio of the 0.5 rpm viscosity to the 100 rpm viscosity; OSM=oligosaccharide mixture obtained from thermally hydrolyzed wood; DDSA=dodecenylsuccinic anhydride; lb/bbl=pounds per 42 gallon barrel; bbl=42 gallon barrel; lb/gal=pounds per gallon; lb/100 ft3=pounds per 100 square feet; kg/m3=kilograms per cubic meter.

Viscosified aqueous chitosan-containing well drilling and servicing fluids