A dermatologically-compatible composition comprising a hydrophilic gel which comprises a blend of a chitosan and a hydrophilic poly(N-vinyl lactam) having a K value of less than 60.

This invention relates to the field of poly(N-vinyl lactam)-chitosan gels and more particularly to gels which are absorbent and may be skin adhering, which are flexible and contour-conforming, and which can be used for a variety of applications. The gels of the present invention have K values of below 60.
Chitosan is a deacetylated chitin, and is a linear polysaccharide of deacetylated N-acetyl-D-glucosamine. Chitosan has been used to absorb heavy metals from water and industrial waste streams, and as a dyeing assistant in photographic emulsions. Chitosan derivatives have also been used in cosmetics and conditioning agents, in hair setting lotions and shampoos as, for example, in U.S. Pat. Nos. 4,134,412 and 4,202,881, when neutralized with acids.
Poly(N-vinyl lactam) s such as polyvinylpyrrolidone (PVP) have been used, for example, in pharmaceuticals, in certain types of films and in some cosmetic products.
It has been known that polyvinylpyrrolidone forms complexes with polyurethanes to yield hydrophilic blends or alloys. U.S. Pat. No. 4,642,267 describes hydrophilic polymer blends of polyurethane and hydrophilic poly(N-vinyl lactam) prepared in solvent solution to provide slippery coatings when wet and which are water insoluble to some extent once cured by drying.
European Patent Application 107,376 describes tacky PVP gels which require the use of ionizing radiation for cross-linking. U.S. Pat. No. 4,646,730 describes a PVP/Silver Sulfadiazine hydrogel dressing in which electron beam radiation is required to cross-link the PVP and form a gel. In addition, magnesium trisilicate, hydrogen peroxide and/or polyacrylic acid are added for color stabilization. It is apparent that there would be an advantage in making skin-adhering gels in the absence of expensive equipment and/or processing.
U.S. Pat. No. 5,420,197 describes poly (N-vinyl lactum)-chitosan gels wherein the K values are at least 60.
Ring opening of pyrrolidone groups on PVP was described by H. P. Frank, xe2x80x9cThe Lactam-Amino Acid Equilibria for Ethylpyrrolidone and Polyvinylpyrrolidonexe2x80x9d, Journal of Polymer Science 12, 565-576 (1954), and A. Conix and G. Smets, xe2x80x9cRing Opening in Lactam Polymersxe2x80x9d, J. Poly. Chem.13, 221-229 (1955). The concept of ring-opened pyrrolidone groups is made use of in this invention to unexpectedly attain absorbent gels.
It is therefore an object of the invention to provide dermatologically-compatible gels having a hydrophilic absorbent property and K values of less than 60.
It is a further object to produce gels with K values of less than 60 without a need for expensive equipment and/or processing.
It is another object to provide gels of poly(N-vinyl lactam) and chitosan derivatives with K values of less than 60 which can be used in a variety of products such as cavity dressings, drug delivery patches, face masks, wound dressings and prostheses.
Accordingly, there is provided a stable, hydrophilic gel which comprises a blend of acid-neutralized chitosan and a poly(N-vinyl lactam), with or without a plasticizer, the poly(N-vinyl lactam) having a K value of less than about 60 and mole equivalents of acid groups of at least about 1.4. The gel may be formed into a wound packing or cavity dressing where, unlike hydrocolloid dressings, it is able to absorb exudate without losing its gel structure. It can also be utilized as a drug carrier for transdermal devices and for use in dry skin masks to deliver moisturizers to the skin. It can also be used in prosthetic devices such as breast implants.
The poly(N-vinyl lactam) is preferably a polyvinylpyrrolidone having mole equivalents of acid groups of at least about 1.4 formed by ring opening of pyrrolidone groups.
The gel is prepared by mixing aqueous poly(N-vinyl lactam) solution and acidneutralized chitosan in aqueous solution at a poly(N-vinyl lactam)/chitosan weight ratio of from about 12/1 to about 1/1, preferably from about 10/1 to about 5/1, to form a blend at about 5 wt. % to 40 wt. % total polymer concentration, preferably from about 12.5 wt. % to about 25 wt. % polymer concentration, and allowing the blend to cure until a gel is formed.
The gel preferably includes at least one additional ingredient which may be releasable from the gel. Preferably the releasable ingredient is a moisturizer, drug or other bio-effecting or body-treating material.
Preferred products for which the gel can be used are cavity-filling wound dressings, other wound and burn dressings, drug delivery systems, cosmetic masks, prostheses and wraps.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description, and its scope will be pointed out in the appended claims.
It has been found that poly(N-vinyl lactam) such as polyvinylpyrrolidone (PVP), with a degree of ring-opened pyrrolidone groups, forms hydrophilic gels with chitosans. The gels are flexible and transparent or translucent and may be used alone or with various additives. The gels can be used for wound packing, wound and burn dressings, drug delivery systems, prostheses, cosmetic face and nail wraps, and other applications where the high absorption capacity of the gel and the high heat capacity and transport capacity of water as part of the hydrophilic gel can be utilized. These gels may have either a tacky quality or a non-tacky quality.
Chitosan, a natural product, is derived from chitin. Chitin is an unbranched linear polysaccharide of N-acetyl-D-glucosamine units linked by xcex2-1,4 bonds. It is a polymer of glucose in which the hydroxyl group on C-2 is replaced by the N-acetylamino group xe2x80x94NHCOCH3. In chitosan, the acetyl group is absent. Therefore, chitosan is a deacetylated chitin. Chitosan contains approximately 7% nitrogen and is structurally similar to cellulose. Chitin occurs in nature in the exoskeletons of arthropods such as crabs, lobsters and shrimp. Chitin can be obtained from these sources as an amorphous powder after dissolution of the calcium carbonate with mineral acids and removal of the proteins. It is also found in some fungi, algae and yeast.
Chitosan becomes soluble in water when protonated with acids. The polymer thus formed is positively charged and thus more likely to interact with negatively charged surfaces like skin and hair.
Chitosan derivatives are commercially available as, for example, chitosan neutralized with pyrrolidone carboxylic acid available as Kytamer PCA from Amerchol Corporation; carboxymethyl sodium salt of chitosan available as Chitisol from Muto Corporation; chitosan neutralized with glutamic acid available as Seacure+210 from Protan Corporation; N,O-carboxymethyl chitosan available from Nova Chem Ltd., Canada; and un-neutralized chitosan available from Tokyo Kasei Inc. Suitable chitosan derivatives for this invention are the dermatologically-compatible salts of chitosan such as those with pyrrolidone carboxylic acid, glutamic acid, acetate, etc., and also N,O-carboxymethyl chitosan.
Suitable poly(N-vinyl lactams) have a K value of less than about 60, preferably less than about 45, most preferably from about 25 to about 35, and optimally about 30. The K value represents kinematic viscosity. It is a measure of the resistive flow of a fluid under the influence of gravity. The K value is derived from viscosity measurements and is calculated according to Eikentscher""s formula described by Kline, G. M., xe2x80x9cPolyvinylpyrrolidonexe2x80x9d, Modern Plastics p 157 (November 1945) and is also described in General Aniline and Film Corporation Technical Bulletin 7583-033. The K value is a function of molecular weight. At the same K value or molecular weight, the level of ring-opened poly(N-vinyl lactam) is an important consideration in determining whether a gel forms.
In the invention, poly N-vinyl lactams containing above certain levels of ring-opened pyrrolidone groups, when mixed with certain solutions of neutralized chitosans, form gels which may be mildly tacky. The term tacky is intended to mean having the property of being sticky to the touch or adhesive to a degree that the gel is capable of sticking to the skin while being easily removable when removal is desired.
The term poly(N-vinyl lactam) as used herein shall be understood to include homopolymers, copolymers and terpolymers of N-vinyl lactams such as N-vinylpyrrolidone, N-vinylbutyrolactam, N-vinylcaprolactam, and the like, as well as the foregoing prepared with minor amounts, for example, up to about 20 weight percent, of one or a mixture of other vinyl monomers copolymerizable with the N-vinyl lactams. Copolymers or terpolymers of poly(N-vinyl-lactam) may comprise N-vinyl-lactam monomers such as vinylpyrrolidone copolymerized with monomers containing a vinyl functional group such as acrylates, hydroxyalkylacrylates, methacrylates, acrylic acid or methacrylic acid, and acrylamides. Of the poly(N-vinyl lactam) homopolymers, the polyvinylpyrrolidone (PVP) homopolymers are preferred. Of the poly(N-vinyl lactam) copolymers, vinyl pyrrolidone, acrylamide copolymers are preferred. A suitable poly(N-vinyl lactam) terpolymer is vinylpyrrolidone, vinylcaprolactam, dimethylarninoethyl methacrylate. A variety of polyvinylpyrrolidones are commercially available. It is important, however, for the poly(N-vinyl lactam) to contain a degree of ring-opened lactam groups.
A lactam may be considered to be a cyclic amide produced from an amino acid through the elimination of a molecule of water from the xe2x80x94COOH and xe2x80x94NH2 groups. A lactam, therefore, contains a xe2x80x94NHxe2x80x94COxe2x80x94group in a ring. An N-vinyl lactam has a vinyl group at the ring nitrogen and the monomer can be polymerized through the vinyl group. In a ring-opened poly(N-vinyl lactam), the vinyl backbone may be considered to remain essentially intact, but some lactam rings are opened to make available xe2x80x94COOH groups. The availability of these xe2x80x94COOH groups may be measured through base titration to determine the mole equivalents of base per mole of acid groups in a specific poly(N-vinyl lactam). Because the polymer backbone remains essentially intact, different poly(N-vinyl lactams) having the same molecular weight or K value may have different levels of ring openings. The poly(N-vinyl lactams) useful in forming the gels in the invention have a mole equivalent/mole of acid groups greater than about 1.4, preferably greater than about 2.0. In the absence of opened lactam rings, the gel does not form. The poly(N-vinyl lactams) are preferably of relatively low molecular weight as indicated by a K value less than about 60. Biological systems break down poly (N-vinyl lactams) which have such K values.
Ring opening in poly(N-vinyl lactams) may be effected by heating a solution of the poly(N-vinyl lactam) at a temperature of from about 50xc2x0 C. to about 120xc2x0 C., with from about 60xc2x0 C. to about 100xc2x0 C. preferred, at pressure from about 15 psi to about 150 psi for from about one half hour to about 10 days, with from about one hour to about 24 hours preferred. The solvent for the solution is preferably aqueous and may include a small amount of a weak base such as dilute ammonium hydroxide or dilute sodium hydroxide to result in a solution which is slightly basic, e.g. having a pH of about 7-9, with about 7-8 or 7-8.5 preferred. If time saving is an important consideration as in commercial operations, ring opening may be carried out, for example, for shorter periods of time in a reactor under conditions of high temperature and pressure, e.g. 200xc2x0 C. at 50 psi.
To form the gel, the poly(N-vinyl lactam) is mixed or blended with neutralized chitosan. At certain ratios of PVP/chitosan derivatives, a mixture of these two components forms a highly water-swellable gel within a short time of mixing.
The gel may be prepared by dissolving the poly(N-vinyl lactam) such as polyvinylpyrrolidone in aqueous solution, then adding an aqueous solution of neutralized chitosan with sufficient agitation to attain a homogenous mixture. The solvent used for the gel preparation is preferably substantially aqueous. For example, the gels may be prepared in water or in hydroalcohols such as water/isopropyl alcohol and water/ethanol. The gels form at a ratio of PVP/chitosan of from about 12/1 to about 1/1, preferably from about 10/1 to about 5/1. At higher PVP to chitosan ratios gels are formed but may lead to a sticky residue and may contain uncomplexed PVP which will leach out in water. The total polymer concentration as well as the ratios of the two polymer components at which the gel is made shows an effect on the consistency of the gel, which becomes softer at lower concentrations. Decreasing the total polymer concentration, or decreasing the concentration of the PVP alone, also leads to softer gels at a given PVP-chitosan ratio. The gels may be made with a total polymer content ranging from about 5 to about 40 wt. % solids, preferably from about 12.5 wt. % to about 25 wt. % solids. At lower solids levels, gels may form but they are not as consistent. The blend may be allowed to cure for a time of from a few seconds to about 20 minutes. The time and temperature for curing are not critical. For purposes of convenience, ambient temperature may be used but the time can be shortened at elevated temperatures. The term gel is intended to mean viscous or semi-solid and jelly-like.
The preferred gels are stable and therefore maintain their physical integrity after absorbing large quantities of liquid. The gels can be sterilized by radiation sterilization. The gels are hydrophilic and capable of absorbing many times their weight in water or at least twice their weight in water. For practical application as described herein, a gel absorbs, for example, from about 4 to 10 times its dry weight in water or saline solution (0.9% NaCl), depending on the ratio of PVP/chitosan. For example, at a ratio of PVP/chitosan of about 2/1, the gel absorbs about 4 times its dry weight (i.e. solids weight) in saline solution; at a ratio of 10/1, it can absorb about 10 times its dry weight in saline solution.
While the exact nature of the mechanism by which the gel forms is not known, and while it is not intended to be bound by theory, it is believed to be caused by pervasive and tight hydrogen bonds between chains. The presence of the ring-opened pyrrolidones, in some undetermined way, plays an imperative role in achieving this goal.
Wetting, dispersing agents or surfactants as are known in the art, such as block copolymers of ethylene oxide and propylene oxide, may be added to the blends in an amount of from about 1 to about 5 weight percent, preferably from about 1 to about 3 weight percent, to reduce adherence to the skin.
Glycerine in an amount of from about 5 to about 50 weight percent, preferably from about 10 to about 30 weight percent may be added to the gel preparation to increase tack and pliability after drying. The glycerine is preferably mixed into the PVP solution prior to adding neutralized chitosan solution. Propylene glycol or low molecular weight polyethylene glycol may also be used.
Many different types of additional materials may be incorporated into the gels including organic salts, inorganic salts at low levels, alcohols, amines, polymer lattices, fillers, surfactants, pigments, dyes, fragrances and so forth as long as they do not interfere with gel formation. Many of these materials can be released from the gel.
The gels of this invention are especially useful as carriers for a wide variety of releasable biologically-active substances having curative or therapeutic value for human or non-human animals. Included among the biologically-active materials which are suitable for incorporation into the gels of the invention are hypnotics, sedatives, tranquilizers, anti-convulsants, muscle relaxants, analgesics, antipyretic agents, anti-inflammatory agents, local anesthetics, antispasmodics, antiulcer agents, antivirals, antibacterials, antifungals, sympathomimetic agents, cardiovascular agents, antitumor agents, and so forth. A biologically-active substance is added in pharmaceutically-active amounts.
Particularly preferred as biologically-active additives are nitroglycerine, scopolamine, pilocarpine, ergotamine tartrate, phenylpropanolamine, and theophylline; also antimicrobials tetracycline, neomycin, oxytetracycline, triclosan, sodium cefazolin, silver sulfadiazine, and also salicylates such as methylsalicylate and salicylic acid, nicotinates such as methyl nicotinate, capsicum and benzocaine. When the gel is to be used, for example, for cosmetic treatment, hydrating agents such as sodium pyrrolidine carboxylic acid may be added. For a hydrating purpose, however, the large amount of water alone which can be absorbed by the hydrophilic gel serves a hydrating function to the skin.
Water-soluble and water-insoluble additives such as those described above may be initially mixed with the aqueous solvent before the gel preparation is begun, may be mixed with the aqueous solution of poly(N-vinyl lactam) or mixed with the aqueous solution of neutralized chitosan during the gel preparation. Water-soluble ingredients are preferably mixed in with the PVP prior to admixing with chitosan. Many water-insoluble ingredients can be mixed with chitosan prior to adding to PVP. One can also emulsify water insolubles by adding surfactants to either the PVP or chitosan. Alternatively, additives may be similarly mixed into the gel preparation after the poly(N-vinyl lactam) is blended with the chitosan. Additives may also be applied to the surface of a gel dressing, for example, by spraying, dipping, brushing or rolling.
The gels can be used to make adsorbent wound packing agents or dressings, skin masks or wraps, drug delivery patches, prosthetic devices, such as breast implants, and dry film products.
When the gel is used as a wound packing or cavity-filling wound dressing, it advantageously provides the desired properties of such dressings, such as (1) biocompatability; (2) ability to conform to a wound cavity; (3) non-adherence to the wound; (4) absorbs exudate; (5) removable in one piece from the wound; (6) holds its physical integrity when swollen with exudate; (7) is not too sticky for handling.
When used as a skin-hydrating mask, the gel has excellent hydrating capacity, advantageously contains no alcohol, and is easily and cleanly removed.
When made into a dry film and used as a skin mask, it provides a flexible, clear, hydrophilic film which adheres to the skin when wetted with water. The film can retain active moisturizers and other ingredients close to the skin, helping in their delivery. The film can also be easily peeled off after a period of time without leaving residues.
To obtain the products of the invention, the gel may be packaged by itself in a mold, in a dry film form, or as a two-part system which requires mixing prior to use; or may be provided on a substrate and covered with a release liner to prevent the gel from sticking to itself. The release liner is removed prior to application to skin. The substrate may fulfill one or several functions including providing reinforcement, providing a gas and liquid barrier, providing a support with air permeability, providing protection for the gel and the area of treatment, etc. Substrate selection to provide the desired properties is known to those skilled in the art.
The gel may be coated or spread onto a backing or substrate by any means known in the art. The gel can be combined with and adhered to a virtually unlimited variety of substrates or backings including resins, metal foils, woven and non-woven webs of natural and synthetic fibers, etc. A backing which provides gas and liquid barrier properties may be a polymer film such as polyurethane. Desirable composites with the gel may also be made using films of polyester, polyvinyl alcohol, or polyvinylidene chloride. When the gel has a barrier substrate, the resulting structure has particular utility as a wound and burn dressing. Moisture is kept in and excess exudate is absorbed to promote healing but bacteria are prevented from entering the wound or burn area, and microbial stasis may be maintained through the incorporation of an anti-microbial agent into the gel to prevent infection. For ease of use, the tacky gel on a backing is covered with a release liner which may be a silicone-coated film or polyethylene.
The gel may be coated onto the backing so that the gel occupies all or part of the backing surface. If the gel occupies part of the backing surface, non-gel coated areas of the backing may be provided with an additional adhesive. A dressing of this type is positioned on the skin so that the additional skin adhesive comes into contact with intact skin while the absorbent gel contacts a wound. The additional adhesive provides a dressing with staying power when the absorbent gel has become substantially saturated with wound exudate thus losing some of its adhesiveness through a dilution effect.
In still another embodiment, the gel may be used in cosmetic preparations such as face masks and nail wraps. The gel serves a hydrating function with or without a backing and a cosmetic effect may be enhanced with the incorporation of other ingredients. A kit for a cosmetic gel may comprise a ready-made gel or two components: a poly(N-vinyl lactam) component and a chitosan component. Other cosmetic agents such as hydrating agents, fragrances, etc. can also be supplied to the ready-made gel or to either component. For use, the components may be mixed and applied. The gel advantageously can be easily peeled off after use. It shall be understood that the term cosmetic means a preparation intended to enhance or improve physical appearance.
In a further embodiment, fragrances may be incorporated into the gel. When the gel is kept moist in a suitable vented container, the fragrance is slowly released as an air freshener.
The following examples are intended to illustrate but not limit the invention.

Gels formed by the interaction of polyvinylpyrrolidone with chitosan derivatives


A substrate having an adherent and stain resistant layer having durability and flexibility, said layer comprising the reaction product of a reactive polyester having free carboxylic acid and/or hydroxyl groups, a hydroxyl terminated polymer including repeat units from an oxetane having pendant xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)nxe2x80x94Rf groups (said Rf groups generally being a fluorinated alkyl group) and an amino resin curative. The substrate may be printed or embossed or both. The coated substrate has both stain resistant properties and dry erase properties with dry erase markers. The coated substrate can be used as prepared or applied to other substrates.

This invention relates to laminates having improved stain resistance due to the incorporation of a polymer having repeat units from an oxetane monomer having pendant fluorinated groups into a stain resistant surface layer. The stain resistant layer can also be adhered to a variety of substrates including polyesters, paper, polyolefins etc. The coatings exhibit dry erase characteristics when dry erase markers are used.
U.S. Pat. No. 4,603,074 sets forth a polyester-amino resin composition that can form a stain resistant layer on plasticized polyvinyl chloride substrates. While this coating was very good with respect to stain resistance and abrasion resistance, it would be desirable to have further increases in cleanability without using solvents, while maintaining stain resistance and abrasion resistance.
A variety of polymeric coatings and surface treatments for natural and synthetic materials have been developed to enhance the dirt and stain release characteristics. Some of the more effective ones to date allow for reapplication of the anti-soil treatment after cleaning (such as with carpets) or in tents.
Dry erase boards and ink or marker pens are popular replacements for chalkboards. A variety of relatively nonporous writing surfaces have been developed along with special dry erase markers that are specially designed to leave strong well defined continuous marks that can be erased with a dry cloth or eraser. U.S. Pat. Nos. 3,834,823; 3,922,457; 3,949,132; 4,746,576; 4,988,123 and 5,324,764; disclose such technology and are herein incorporated by reference for their teachings on dry erase systems.
U.S. Pat. No. 5,650,483 describes the preparation of oxetane monomers useful to form oxetane polymers with pendant fluorinated chains. The oxetane polymers were characterized as having low surface energy, high hydrophobicity, and a low coefficient of friction. That patent is incorporated by reference herein for its teachings on how to prepare the oxetane monomers and polymers. In the reference the oxetane polymers could be formulated with isocyanates to form crosslinked compositions. Additional patents issued on variations of the oxetane monomers and polymers. These were U.S. Pat. Nos. 5,654,450; 5,663,289; 5,668,250, and 5,668,251 also incorporated herein by reference.
According to the present invention, an improved stain and abrasion resistant polymeric layer was developed by incorporating a minor amount of a hydroxyl terminated polymer having repeat units from an oxetane monomer having pendant fluorinated groups thereon into a polyester-amino resin composition. The hydroxyl terminated polymer may have other repeat units such as derived from the ring opening polymerization of cyclic ethers including tetrahydrofuran and/or more conventional ring opening polymerization of oxetane or epoxy monomers. Excellent stain release and abrasion release are observed with as little as 0.1, 0.2 or 0.5 to 10 or 15 parts by weight of repeat units from the oxetane monomer with pendant fluorocarbon groups based on 100 parts of polyester resin and amino resin in the dry coating. The coating may be as thin as 0.1 to 2 or 4 mil (thousandths of an inch) thick. One preferred embodiment is a layer of a flexible vinyl chloride polymer coated with said polyester-amino resin composition in solvent and heated to cure and adhere the resin to the vinyl chloride polymer layer with removal of the solvent. This provides the flexible vinyl chloride polymer layer with a coating which is stain resistant or which can readily be cleaned (either dry or with solvent) without significant abrasion to remove stains.
The vinyl chloride layer may be a vinyl chloride polymer, which is a plastisol coated and fused or is a plasticized vinyl chloride polymer composition which has been calendered or extruded. The vinyl chloride may be applied to a backing, substrate or support. In either case the polyvinyl chloride layer (about 1 to 30 or 100 mils thick) can be printed one or more times. The printed layer can be embossed, before and/or after printing, and finally coated with a layer of a solution of a said polyester-amino resin composition and cured to provide the vinyl chloride polymer layer with an outer stain resistant layer about 0.1 to 2 or 4 mils or more thick.
The reactive polyester-amino resin for use as the outer or top coating on a substrate is prepared from a solution of a reactive polyester (alkyd resin) and an amino resin in a solvent (such as methyl ethyl ketone, water, alcohols, or combination thereof) containing a catalyst such as p-toluene sulfonic acid and is applied at a temperature desirably of at least about 150, 200, 250, or 400xc2x0 F. or more (66, 93, 121, or 204xc2x0 C.) to cause curing or cross-linking of the polyester resin and the amino resin. The reactive polyester-amino resin composition may be applied to a substrate (e.g. vinyl chloride polymer, polyester, cellulosic, polyolefin composition) directly or with an intermediate tie layer. The substrate may be with or without a backing or substrate, with or without the printing and with or without the embossing. A preferred embodiment includes the catalyzed reactive polyester-amino resin solution being applied over a tie layer to an embossed and printed compounded and plasticized vinyl chloride polymer composition carried on a suitable backing or substrate. Such vinyl chloride polymer based substrates are readily available from wallcovering manufacturers.
The polyester resins (alkyd resins) are made by a condensation polymerization reaction, usually with heat in the presence of a catalyst, or a mixture of a polybasic acid and a polyhydic alcohol. Fatty monobasic oils or fatty acids, monohydroxy alcohols and anhydrides may be present. The polyester contains active hydrogen atoms, e.g., carboxylic acid groups and/or hydroxyl groups for reaction with the amino resin. Example of some acids to use to form the alkyd resin or reactive polyester are adipic acid, azelaic acid, sebacic acid, terephthalic acid, phthalic anhydride, and so forth. Examples of some polybasic alcohols include ethylene glycol, propylene glycol, diethylene 3 glycol, dipropylene glycol, glycerine, butylene glycol, 2,2-dimethyl-1,3-propanediol, trimethylol propane, 1,4-cyclohexanedimethanol, pentaerythritol, trimethylolethane and the like. Mixtures of the polyols and polycarboxylic acids can be used. An example of a suitable reactive polyester is the condensation product of trimethylol propane, 2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, phthalic anhydride and adipic acid. Mixtures of these reactive polyester or alkyd resins can be used. Alkyd resins are well known as shown by the xe2x80x9cEncyclopedia of Polymer Science and Technology,xe2x80x9d Vol. 1, 1964, John Wiley and Sons, Inc., pages 663-734; xe2x80x9cAlkyd Resins,xe2x80x9d Martens, Reinhold Publishing Corporation, New York, 1961 and xe2x80x9cAlkyd Resin Technology,xe2x80x9d Patton, Interscience Publishers, a division of John Wiley and Sons, New York, 1962. Some unsaturated polybasic acids and unsaturated polyols may be used in the condensation reaction but are generally undesirable. The reactive polyester (alkyd resin) is usually added to the amino resin while dissolved or suspended in a solvent, e.g. such as a mixture of polyester in a ketone and an alkyl acetate at about 60-80% solids or a mixture of polyester in alkyl alcohols and alkylene glycol alkyl ethers.
Alternatively to using a separate polyester and hydroxyl terminated polymer including repeat units from an oxetane monomer having a pendant pendant xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)nxe2x80x94Rf one can react said hydroxyl terminated polymer into the polyester thus replacing two components with a single component. The hydroxyl terminated polymer is more completely bound into the network as a result of prereacting the polyester forming components with the hydroxyl terminated polymer and is therefore less likely to be removed from the coating by wear or cleaning. In the claims the polyester including the repeat units derived from copolymerizing said hydroxyl terminated polymer into said polyester is described as a reactive polyester resin including therein at least one repeat unit derived from copolymerizing into said polyester a hydroxyl terminated polymer including repeat units from an oxetane having a pendant xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)nxe2x80x94Rf group. One skilled in the art would be able to optimize reaction conditions for forming such a polyester such that the oxetane repeat units are incorporated into the polyester. Such reaction conditions may include prereaction of the dibasic acid and the oxetane polymer having a pendant xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)nxe2x80x94Rf in a separate reaction and then adding the remaining diacids and polyols to complete the polymerization of the polyester.
The amino resin to be reacted with the reactive polyester is an alkylated benzoguanamine-formaldehyde, an alkylated urea-formaldehyde or, preferably, an alkylated melamine-formaldehyde resin. Mixtures of these resins can be used. The alcohol used to modify the benzoguanamine-formaldehyde, urea-formaldehyde or melamine-formaldehyde resin can be n-butanol, n-propanol, isopropanol, ethanol or methanol and so forth. These amino resins are well known and include those set forth in xe2x80x9cAminoplastics,xe2x80x9d Vale et al, lliffe Books Ltd., London, 1964; xe2x80x9cAmino Resins,xe2x80x9d Blair, Reinhold Publishing Corporation, New York, 1959, xe2x80x9cModern Plastics Encyclopedia 1980-1981,xe2x80x9d pages 15, 16 and 25 and xe2x80x9cEncyclopedia of Polymer Science And Technology,xe2x80x9d John Wiley and Sons, Inc., Vol. 2, 1965, pages 1 to 94.
Sufficient amounts by weight of the reactive polyester and amino resin are employed to provide a stain resistant, layer having good durability and flexibility and having good adhesion to the substrate. These materials are desirably cured at temperatures of at least 150, 200, 250 or 400xc2x0 F. or more (66, 93, 121, or 204xc2x0 C.) for effective times in the presence of a minor amount by weight of an acidic catalyst such as boric acid, phosphoric acid, acid sulfates, hydrochlorides, phthalic anhydride or acid, oxalic acid or its ammonium salts, sodium or barium ethyl sulfates, aliphatic or aromatic sulfonic acids such as p-toluene sulfonic acid (preferred), methane sulfonic acid and the like. It is important that the stain resistance imparted by the polyester and amino resin be optimized by controlling things such as glass transition temperature, crosslink density and the presence of molecules that may act as plasticizers or other molecules that may transport or attract staining molecules in the coating. Prior to curing flatting agents or other additives can be added to the mixture of the reactive polyester and amino resin.
The hydroxyl terminated polymer(s) including repeat units from an oxetane having a pendant xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)nxe2x80x94Rf group are prepared. These can be prepared according to the teachings of U.S. Pat. Nos. 5,650,483; 5,668,250 and 5,663,289 hereby incorporated by reference for those teachings. The oxetane monomer desirably has the structure
wherein n is an integer from 1 to 3 and Rf, independently, on each monomer is a linear on branch alkyl group of 1 to 20 carbon atoms with a minimum of 25, 50 or 75 percent of the H atoms of said Rf being replaced by F and optionally up to all of the remaining H atoms being replaced by l, Cl or Br, or each Rf, independently, being an oxaperfluorinated polyether having from 4 to 60 carbon atoms; R being H or an alkyl of 1 to 6 carbon atoms; preferably Rf has at least 85 and more preferably at least 95% of said H atoms replaced by F. Preferably said linear or branched alkyl group is of from 1 or 3 to 7 or 10 carbon atoms.
The repeat units from said oxetane monomers desirably have the structure
where n, Rf, and R are as described above.
The hydroxyl terminated polymer(s) including repeat units from said oxetane monomers can have one or more terminal hydroxyl groups. They desirably have number average molecular weights from about 250; 500; 1,000 or 5,000 to about 50,000 or 100,000. The polymer(s) can be a homopolymer or a copolymer of two or more different oxetane monomers. The polymer may also be a copolymer of cyclic ether molecules having from 2 to 4 carbon atoms in the ring such as tetrahydrofuran and one or more oxetane monomers as described in the previously incorporated U.S. Pat No. 5,668,250. The copolymer may also include copolymerizable substituted cyclic ethers such as substituted tetrahydrofurans. The repeat unit from a tetrahydrofuran monomer has the formula to xe2x80x94(Oxe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94). The hydroxyl terminated polymer(s) optionally includes a cyclic tetramer of said oxetane monomer, which may be a byproduct of the polymerization. In some embodiments, said hydroxyl terminated polymer includes up to 10, 20, or 30 wt % of said tetramer based on the weight of said hydroxyl terminated polymer(s).
It is desirable that the polymer including repeat units from an oxetane having a pendant xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)nxe2x80x94Rf group has one or more hydroxyl group in that this provides a possible mechanism for this polymer to be chemically bound into the polyester-amino resin composition. It is acknowledged that the amount of such bound polymer has not been measured in the examples and it may be a small or large percentage of the total polymer with said oxetane repeat units. In some embodiments it may be desirable to prereact the hydroxyl terminated polymer with the polyester component to increase the percentage of hydroxyl polymer bound into the coating. It is also acknowledged that the percentage of the polymer with said oxetane repeat units and the oxetane repeat units themselves may not be uniformly distributed through the bulk of the coating. Said oxetane repeat units may be disproportionately present at the surface of the coating due to the low surface tension of those repeat units.
The amount of the various components in the coating will be generally specified in relationship to 100 parts by weight of the polyester resin and the amino resin crosslinking agent. The weight ratio of polyester resin (neat) to amino resin (neat) can vary widely but desirably is from about 10:90 to 90:10 and more desirably from about 20:80 to 80:20. Generally it is more desirable to match the moles of reactive groups on the polyester to within 10 to 20% to the number of moles of reactive groups on the amino resin. The number of moles of reactive groups can be determined by dividing the weight of the component by the equivalent weight for the component. The term xe2x80x9cneatxe2x80x9d after polyester and amino resin does not exclude using polyesters and amino resins that are received dissolved in solvents but rather specifies that the amount used is to be recalculated based on the weight without the solvent. For the purposes of this disclosure no distinction will be made whether the amino resin crosslinks the polyester resin or visa versa.
The amount of carriers and/or solvent(s) in the coating composition can vary widely depending on the coating viscosity desired for application purposes, and solubility of the components in the solvent. The solvent(s) can be any conventional solvent for polyester-amino resin systems. These carriers and/or solvents include but are not limited to water, alkyl alcohols of 1 to 10 carbon atoms, ketones of from 3 to 15 carbon atoms e.g. methyl ethyl ketone or methyl isobutyl ketone, alkylene glycols and/or alkylene glycol alkyl ethers having from 3 to 20 carbon atoms, acetates and their derivatives, ethylene carbonate, etc. Illustrative U.S. patents of the carrier and/or solvent systems available include U.S. Pat. Nos. 4,603,074; 4,478,907; 4,888,381 and 5,374,691 hereby incorporated by reference for their teachings both of carriers and/or solvent systems and of polyesters and amino resins. The amount of solvent(s) can desirably vary from about 20 parts by weight to about 400 parts by weight per 100 parts by weight of total polyester resin and amino resin.
The amount of the oxetane repeat units having a pendant CH2xe2x80x94Oxe2x80x94(CH2)nRf group is desirably from about 0.1 or 0.2 to about 10 or 15 parts by weight and more desirably from about 0.5 to about 10 or 15 parts by weight per 100 parts total weight of said polyester resin and amino resin. Of course if the hydroxyl terminated polymer(s) including repeat units from said oxetane has a significant amount of repeat units from tetrahydrofuran or other repeating unit therein, the hydroxyl terminated polymer""s weight will exceed that of said oxetane repeat units.
The amount of catalyst is an amount that effectively catalyzes the mutual crosslinking of the polyester and amino resins under the crosslinking conditions chosen (usually elevated temperatures). As the crosslinking temperature increases above 150, 200, 250, or 400xc2x0 F. (66, 93, 121, or 204xc2x0 C.) the amount of catalyst can be reduced. Effective amounts of catalyst can vary from about 0.1, 0.5 or 1 to about 6 or 8 parts by weight and preferably from about 2 or 3 to about 6 parts by weight per 100 parts by weight total of said polyester and amino resins.
Conventional flattening agents can be used in the coating composition in conventional amounts to control the gloss of the coating surface to an acceptable value. Examples of conventional flattening agents include the various waxes, silicas, aluminum oxide, alpha silica carbide, etc. Amounts desirably vary from about 0 or 0.1 to about 5 or 10 parts by weight per 100 parts by weight total of said polyester and amino resins. For most embodiments high gloss is preferred.
Additionally other conventional additives for polyester and amino resin compositions or for other clear coating applications in general can be used in the composition. Examples include viscosity modifiers, antioxidants, antiozonants, processing aids, pigments, fillers, ultraviolet light absorbers, adhesion promoters, emulsifiers, dispersants, etc.
While this disclosure generally teaches applying the dry-erase coating directly to a substrate, it also provides for intermediate coating(s) between the substrate and the dry erase coating. These intermediate coating(s) can be decorative coatings to provide a colored background or a printed (patterned) background. Alternatively or additionally they can be a buffer between the substrate and the dry-erase coating preventing interaction between the dry-erase coating and the substrate. Or they can prevent interaction between components in the substrate and components in the dry-erase coating (e.g. keeping plasticizer from the substrate from migrating into the coating). An intermediate coating(s) may also function to improve adhesion of the dry erase coating to the substrate when adhesion is a concern. An example where adhesion might be improved is with a polyolefin (polyethylene or polypropylene) substrate which may be plasma or corona surface treated or have a hydrocarbon intermediate adhesive layer applied thereto before the dry-erase coating is applied.
The substrates may be any material which would benefit from a stain resistance or dry-erase coating. Examples include cellulosic products (coated and uncoated paper, boardstock, cardboard, wood and paneling), fibers, synthetic polymers (including polyolefins, polyesters, polycarbonates, polystyrene, poly (methacrylates) and especially highly filled or highly plasticized ones which are more permeable towards stains e.g. polyvinyl chloride), metals (requiring temporary or permanent protection from stains), and ceramics.
The coating composition can be prepared by a variety of mixing techniques. Most of the components can be prediluted or precombined with other components. When the catalyst, polyester resin, and amino resin are combined, they can begin to crosslink. A convenient formulation procedure is to combine the polyester resin, solvent(s), amino resin, and any non catalyst additives in one container. In a separate container the catalyst and optionally solvent can be stored. Shortly before application the catalyst can be combined and mixed with the other components.
The substrate with stain resistant layers of the present invention re particularly useful as dry erase writing surfaces (including boards, posters, papers, clipboards, menus, etc.) wallcoverings, anti graffiti surfaces e.g. in public areas including restrooms, and in kitchens and food preparation areas. However, these stain resistant laminates, also, can be used in the manufacture of tablecloths, shoe uppers, luggage exteriors, upholstery, vehicle interiors and seats, golf bags and other sporting goods and so forth.
The polyvinyl chloride can be an emulsion (plastisol grade) or a suspension grade vinyl chloride polymer. The vinyl chloride polymer can be polyvinyl chloride homopolymer (preferred) or a copolymer of a major amount by weight of repeat units from vinyl chloride and a minor amount by weight from a copolymerizable monomer selected from the group consisting of vinyl acetate, vinylidene chloride and maleic ester. Bulk and solution vinyl chloride polymers, also may be used. Mixtures of vinyl chloride polymers can be used. Vinyl chloride polymers and copolymers are well known and include those set forth in xe2x80x9cVinyl and Related Polymers,xe2x80x9d Schildknecht, John Wiley and Sons, Inc., New York, 1952; Sarvetnick, xe2x80x9cPolyvinyl Chloride,xe2x80x9d Van Nostrand Reinhold Company, New York 1969; Sarvetnick, xe2x80x9cPlastisols and Organosols,xe2x80x9d Van Nostrand Reinhold Company, New York, 1972 and xe2x80x9cModern Plastics Encyclopedia 1980-1981,xe2x80x9d October, 1980, Volume 57, No. 10A, McGraw-Hill Inc., New York.
The amount of plasticizer used to plasticize the vinyl chloride polymer to make it flexible may vary from about 20 or 30 to about 100 parts by weight per 100 parts by weight of total vinyl chloride polymer resin more desirably from about 20 or 30 to about 50 or 60 parts by weight for wallpaper applications and from about 60 to about 100 parts by weight for upholstery type applications per 100 parts by weight of total polyvinyl chloride. Any conventional plasticizer for PVC can be used. Examples of plasticizers which may be used are butyl octyl phthalate, dioctyl phthalate, hexyl decyl phthalate, dihexyl phthalate, diisooctyl phthalate, dicapryl adipate, dioctyl sebacate, trioctyl trimellitate, triisooctyl trimellitate, triisononyl trimellitate, isodecyl diphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, polymeric plasticizers, epoxidized soybean oil, octyl epoxy tallate, isooctyl epoxy tallate and so forth. Mixtures of plasticizers may be used.
Other vinyl chloride polymer compounding ingredients are desirably incorporated in the vinyl chloride polymer compositions. Examples of such ingredients are the silicas such as precipitated silica, fumed colloidal silica, calcium silicate and the like, calcium carbonate, ultra violet light absorbers, fungicides, carbon black, barytes, barium-cadmium-zinc stabilizers, barium-cadmium stabilizers, tin stabilizers, dibasic lead phosphite, Sb2O3, zinc borate, molybdates such as ammonium octa-molybdates, aluminum oxide, aluminum trihydrate and so forth and mixtures of the same. TiO2, red iron oxide, phthalocyanine blue or green or other color pigments can be used. The pigments and the other dry additives preferably are dispersed or dissolved in one or more plasticizers before adding to the plasticized vinyl chloride polymer compositions. These compounding ingredients are used in effective amounts by weight to control color, mildew, stabilization to ultra-violet light and heat, viscosity and so forth of the plasticized vinyl chloride polymer.
The vinyl chloride polymer composition may contain suitable blowing or foaming agents such as sodium bicarbonate, and the organic agents like 1,1-azobisformamide, 4,4-oxybis (benzene sulfonylhydrazide), p-toluenesulfonyl hydrazide, or water and so forth to form a cellular or foamed vinyl chloride polymer composition layer or sheet on fusing. The blowing agents may require an activator. Such blowing agents are well known.
Vinyl chloride polymer blending or extender resins, also, can be used in the compositions in a minor amount by weight as compared to the vinyl chloride polymer composition.
The ingredients forming the vinyl chloride polymer composition may be charged to and mixed together in any one of several mixing devices such as a Ross Planetary mixer, Hobart dough type mixer, Banbury, 2-roll rubber mill, Nauta mixer and ribbon blender and so forth.
The vinyl chloride polymer composition can be formed into layers of films, which can be unsupported or supported (preferred). Where a vinyl chloride polymer plastisol composition is used, it may be cast on a release surface and heated to fuse it to form a film. Where a plasticized suspension grade vinyl chloride polymer composition is used, it can be calendered or extruded and fused to form a film. Temperatures may vary from about 200 to about 400xc2x0 F. (93-204xc2x0 C.). However, it is preferred that in either case the compounded vinyl chloride polymer compositions be supported or have a backing. In the case of the supported vinyl chloride polymer composition, the substrate can be a woven fabric (drill, scrim, cheesecloth, and so forth), a knit fabric, a non-woven fabric, paper etc. The fabric can be continuous, discontinuous, woven, nonwoven, bundled etc and made of cotton, cellulose, nylon, polyester, aramid, glass, rayon or acrylic fibers or cords or mixtures of the same. It may be necessary in some instances to treat the fabric with an adhesive coating or dip to adhere or improve adhesion of the fabric to the vinyl chloride polymer composition.
The vinyl chloride polymer composition film or layer, supported or unsupported, is preferably printed on the surface with a suitable vinyl chloride polymer receptive ink to form desirable and novel pattern and/or design. Such inks are well known and can be applied by various methods of printing such as by gravure, flexography, screen printing, jet printing, web printing, non-impact printing and so forth as for example, set forth in xe2x80x9cModern Plastics Encyclopedia 1980-1981,xe2x80x9d pages 464-465. The printing operation may be repeated for up to five times or more to vary the colors and designs at temperatures of desirably from about 150 to about 165xc2x0 F. (66-74xc2x0 C.) for each printing step.
The vinyl chloride polymer composition film or layer, supported or unsupported, printed or unprinted, is preferably embossed to texture the vinyl chloride layer to provide a pattern or design for esthetic or functional purposes. Embossing of thermoplastic films, layers or sheets is well known and is usually carried out by passing the film between an embossing roll and a backup roll under controlled preheating and post-cooling conditions. See xe2x80x9cModern Plastics Encyclopedia 1980-1981,xe2x80x9d pages 454-45. Additional decorating or printing can sometimes be done with the above stated inks over the embossed vinyl chloride polymer surface for better aesthetic purposes.


The present invention is a wellhead system for use in completing at least two well bores from within a single conductor housing. The wellhead system comprises at least one wellhead housing which is supported on the conductor housing and which comprises a top portion that is adapted to be connected to a lower portion of a wellhead component, a casing hanger which is supported within the wellhead housing and from which a casing string is suspended, and a connector for securing the wellhead component to the wellhead housing. In accordance with the present invention, the connector is selected from the group consisting of a latch ring and a segmented clamp assembly.

The present invention relates to a side-by-side wellhead system which may be used to drill and complete a number of hydrocarbon wells. More particularly, the present invention relates to a side-by-side wellhead system which comprises one or more high strength, low profile connectors to secure the wellhead housing component of the system to certain other components, such as a drilling riser or a christmas tree.
Prior art side-by-side (SXS) wellhead systems are commonly used to drill and complete a number of hydrocarbon wells from within a single conductor housing. As shown in FIG. 5, such a wellhead system may comprise a base plate 74 which is welded to the top of a conductor housing 70, two casing strings 76a and 76b which are each suspended from the base plate, and a landing support ring 72 which is bolted to the top of the base plate. In this example, the well on the right hand side of FIG. 5 is covered by an abandonment cap 78, which is connected to the top of the landing support ring 72 with a bolted flange connection that comprises a number of bolts 80. In addition, a wellhead housing 60 is installed in the well on the left hand side of FIG. 5 and is connected to the landing support ring 72 using a bolted flange connection which includes a number of bolts 66, only one of which is shown. Furthermore, in the drilling mode of operation of the SXS wellhead system shown in FIG. 5, a drilling riser 62 is connected to the top of the wellhead housing 60 via a bolted flange connection which comprises plurality of bolts 64, only one of which is shown.
The bolted flange connections which are used to connect the various components of prior art SXS wellhead systems are time consuming to install and remove. In addition, the offset loading inherent in SXS wellhead systems limits the maximum operating pressures such bolted flange connections can safely withstand. Furthermore, the flanges themselves occupy a substantial portion of the available cross-sectional area of the wellhead housing, thus reducing the maximum diameter of well casing which can be used in the SXS wellhead system.
These and other limitations in the prior art are addressed by providing a wellhead system for use in completing at least two well bores from within a single conductor housing. The wellhead system comprises at least one wellhead housing which is supported on the conductor housing and which comprises a top portion that is adapted to be connected to a lower portion of a wellhead component, a casing hanger which is supported within the wellhead housing and from which a casing string is suspended, and a connector for securing the wellhead component to the wellhead housing. In accordance with the present invention, the connector is selected from the group consisting of a latch ring and a segmented clamp assembly.
In one embodiment of the invention, the wellhead component comprises a christmas tree which includes a lower connection portion that is received within the top portion of the wellhead housing and the connector comprises a radially expandable latch ring which is disposed between the lower connection portion and the wellhead housing. In addition, the latch ring is supported on the lower connection portion and is expandable into a groove which is formed on the wellhead housing to thereby secure the christmas tree to the wellhead housing.
In another embodiment of the invention, the wellhead component comprises a drilling riser and the connector comprises a segmented clamp assembly which is secured around the wellhead housing and the drilling riser. In addition, the segmented clamp assembly extends around the wellhead housing and the drilling riser an angle of less than 360xc2x0. Furthermore, where the wellhead system comprises three wellhead housings, the segmented clamp assembly extends around the wellhead housing and the drilling riser an angle of approximately 225xc2x0. Moreover, the segmented clamp assembly is preferably supported on the drilling riser prior to being engaged with the wellhead housing.
Thus, the SXS wellhead system of the present invention uses a segmented clamp assembly during the drilling mode of operation, and an internally latching connector during the completion and/or temporary abandonment mode of operation. These types of connectors offer several advantages over the bolted flange connections used on existing SXS systems. Both the segmented clamp assembly and the internally latching connector allow for greater operating pressures within the system because they are able to withstand greater bending moments than the bolted flange connections used on existing SXS systems. In addition, the reduced profile of the internally latching connector allows for larger casing strings to be suspending in a given wellhead housing. Furthermore, the use of an internally latching connector in the production mode of operation provides a cost effective method for connecting the tree to the wellhead housing, since there is no need to leave a permanent segmented connector on the wellhead housing.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.

High pressure side-by-side wellhead system


A hologram is fabricated by opening a volume phase reflection hologram formed in a recording medium such as a positive photoresist. The opening occurs by forming a second hologram, such as an off-axis hologram, in the same recording medium. The opened hologram can be replicated in metal and the metal can be used to emboss the fringe pattern of the opened hologram into plastic. A full range of colors in the visible spectrum may be obtained by metallizing the embossed plastic structure and then by overcoating it with appropriate clear dielectric layers.

A hologram is a recording of an interference fringe pattern between two beams of light. One of these beams usually comprises light reflected from a real object and is called an "object beam," while the other beam is usually a pure and unmodulated beam and is called a "reference beam." If the object beam is pure and unmodulated like the reference beam, then a set of regular interference fringes is recorded and the hologram is referred to as a holographic diffraction grating. When a hologram is illuminated with only the reference beam, the object beam is exactly reproduced in phase and amplitude.
There are two types of holographic recording configurations that are in prevalent use today. The first is called an off-axis, or "Leith-Upatniaks," hologram. In forming this type of hologram, the object beam and the reference beam impinge upon a recording medium from the same side and from directions which are separated by a small angle. As shown in FIG. 1, the planes of the resulting interference fringes, which planes bisect the angle, are formed substantially perpendicular to the surface of the recording medium. Holographic diffraction gratings and embossed display holograms in use today are predominantly formed from this type of hologram.
This hologram is considered to be an improvement over the original hologram invented by Gabor, before the advent of the laser and its coherent light made off-axis configuration possible. With the Gabor, or in-line hologram, the object and reference beams fall in a line on the same axis. Because of the considerable difficulties involved in separating these beams, this hologram never came into wide use. As shall be seen later, however, one embodiment of the present invention exploits this configuration to useful advantage.
Embossed display holograms are typically formed from off-axis holograms in a multi-step process. The first step usually involves making a primary off-axis hologram where the real object is positioned some distance from the surface of the recording medium and the reference beam is a collimated or parallel beam. The second step usually involves illuminating the primary off-axis hologram with a collimated beam of light to project a real image of the object into space. A second hologram is then made by positioning a new recording medium at the position of the projected real image and by introducing a new reference beam at an angle. After development, the second hologram can be viewed under ordinary white light instead of laser light because color blurring is minimized for a focused image. Such a process is described in an article entitled "The Newport Button: The Large Scale Replication Of Combined Three- And Two-Dimensional Holographic Images," by J. J. Cowan, Proc. of SPIE, Vol. 462 Optics in Entertainment II, 1984, pp. 20-27.
In the second step described above, if the primary hologram is illuminated with a narrow slit of light instead of with a full aperture beam, the real image is brighter and deeper, but it exhibits parallax in the horizontal direction only and in a spectral hue of colors from blue to red in the vertical direction. The resulting "rainbow" hologram is the particular type of off-axis hologram which is most widely used today for embossed holograms.
In making embossed holograms, the recording medium used in the second step described above is typically photoresist. Photoresist is a material which, when developed, yields a surface profile whose depth is proportional to the intensity of the incident interference fringes. Since the intensity of the interference fringes of most holograms is essentially sinusoidal, the etch depth profile of the surface of a developed hologram resembles a sine wave when viewed on edge.
The third step of making an embossed hologram usually involves coating the surface of the photoresist of the hologram made in the second step with a conducting metal like silver and immersing the coated hologram in an electroplating bath to plate a layer, such as a layer of nickel, thereon. The fourth step involves using the nickel plate layer as a hard master to emboss the interference pattern into plastic that has been softened by heat, pressure, solvents or some combination thereof in a continuous fashion Finally, in the last step, after embossing, the plastic is typically coated with a highly reflecting metal, like aluminum, to enhance the diffraction efficiency of the embossed hologram.
The second type of hologram in prevalent use today is a volume phase reflection (VPR), or "Denisyuk," hologram. In forming this type of hologram, the object beam and the reference beam impinge upon the recording medium from opposite sides and from opposite directions. As shown in FIG. 2, the planes of the resulting interference fringes are formed substantially parallel to the surface of the recording medium. These planes are spaced apart within the recording medium at a distance which is equal to one-half the wavelength of the recording light divided by the index of refraction of the recording medium. Typical recording media used in the art are fine grained silver halide emulsions--for which the interference fringe planes comprise regions of high density of developed silver--or dichromated gelatin or photopolymer--for which the interference fringe planes comprise regions of slight differences in the index of refraction in comparison with lower exposed regions When a VPR hologram is illuminated with white light, only light having the same wavelength as that of the light that was used in recording is reflected back to the viewer. This occurs because the interference fringe planes that are stacked a half wavelength apart will only coherently backscatter light of that wavelength, i.e., they allow constructive interference. All other wavelengths destructively interfere and are scattered out of the field of view because they do not match the spacing of the planes.
A VPR hologram advantageously allows viewing at full parallax and in a single color, rather than the whole spectrum of colors which is characteristic of an off-axis hologram. Further, high diffraction efficiencies can be achieved without requiring a reflective metallic coating. Still further, a VPR can be viewed from almost any angle of illumination, whereas an off-axis hologram can usually be viewed only with overhead illumination.
Notwithstanding the above-described advantages of a VPR hologram, it has not generally been considered to be feasible to replicate this structure by embossing because the fringe structure comprises a stack of parallel planes disposed within the body of the recording medium. This occurs because development of a photoresist necessarily stops at the first layer. Consequently, VPR holograms are presently replicated by optical, rather than mechanical means, and only then by using a laser. The presently known, and conventional, method of replicating VPR holograms comprises the following steps: (1) making a master hologram recording plate by directing an object beam and a reference beam to impinge upon a first recording medium from opposite sides; and (2) placing a second recording plate in front of the developed master plate and passing a second reference beam therethrough--the object light from the master is reflected and passes in the opposite direction to the second reference beam in the second recording plate and a new VPR hologram will be recorded in the new recording plate. Conventional VPR holograms can be mass replicated.
As a result, there is a need in the art for a volume phase reflection hologram which can be easily replicated.


A motor-driven stair climbing device (10) to carry equipment and goods, more particularly wheel chairs (9) with disabled persons. The wheel chair (9) can be detachably fixed to the stair climber (10) and essentially comprises a stable frame (101) with an energy source (8.1, 8.2), a drive shaft (18), a drive control, feelers (7,131,132), sensors (7) and a lifting mechanism to climb the steps. The stair climbing device is characterized in that a support device (30, 33) is provided, which is supported on the following step of the stairs (1.2, 1.3) and in that the entire center of gravity (5) of the stair climber (10), the wheeler chair (9) and the disabled person is located between the support points of the running wheel (12) or the support device (30, 330) on the steps of the stairs (1.1, 1.2, 1.3).

The invention relates to motor-driven stair climbing devices for conveying equipment and goods, in particular wheelchairs with handicapped persons, in connection with which the wheelchair is attached removably to the stair climber, according to the introductory clause of claim 1.
Motor-driven stair climbing devices are known. Two construction principles are widely known for conveying wheelchairs with handicapped persons. One construction principle uses numerous wheels that rotate not only around their own axle but at the same time around an axle shared by all wheels. Cf. DE-C 37 13 564 or DE-C 32 26 294. On these devices, on the one hand it is advantageous that only rubber-tired wheels come into contact with the stairway and particularly the edge of the stairs, such that damage is largely ruled out; on the other hand, it is very dangerous that the wheels can only engage the steps to a limited depth. Operating these devices thus requires special cautious and circumspection, last but not least because the load consists of a person. In reality, however, stairways come in many designs: they range from relatively flat stairways running completely straight to narrow, steep winding stairways. Climbing stairways with stair climbers based on the multiple-wheel principle is not risk-free, because the apparatus can tilt over. The stair climber, the wheelchair and the person therefore have to be kept balanced by a strong operator.
The second widely known principle of construction uses two parallel crawlers. The crawlers are long enough that at least three stairs can be grasped at the same time. Accidental tipping over of the wheelchair and the person is thus no longer possible, thus eliminating falls with resulting injuries or even cases of death. Because of the length of the crawlers, however, these stair climbers have problems moving on narrow and curved stairways.
Finally, a stair climbing device has already been proposed that works with a spider-like leg system. However, such a device requires a highly complicated system of touch and position sensors and corresponding actuators that can only be controlled by means of a highly complex computer program in order to prevent the occurrence of missteps or dangerous inclinations of the platform carrying the wheelchair. A practical implementation of this spider leg principle is not yet known.
The present invention is based on the technical problem of indicating a stair climbing device of the type mentioned in the beginning that is not only so light and space-saving that it can be attached removably to any desired goods to be conveyed and in particular to wheelchairs, but also offers a particularly high degree of safety.
This technical problem is solved by a stair climbing device with the features of claim 1.
Thanks to the present invention, the stair climber always stands on two steps, namely either on the next steps or, if the stairway is not too narrow or too winding, on the steps after the next ones. The person operating the stair climber is thereby relieved as much as possible in terms of force; henceforth he/she only has guiding and steering tasks. Using the construction principle according to the invention, it would even be possible to build operator-free stair climbers.
A further advantage is that the support device can be built relatively short because it only needs to bridge over one or two stairs. Since it can also be built very narrow, narrowly winding stairways do not pose problems either.
According to an advantageous design of the invention, the support device is attached to the stair climber. In this way the object conveyed, in particular the wheelchair, remains unmodified.
According to a first design of the invention, the support device executes a linear lift movement. Linearly moving support devices can be one or more telescoping feet or also one or more scissor legs.
This action is comparable to a healthy person""s climbing of stairs.
If the support device is designed advantageously in such a way that it can execute a swinging movement, in addition to the linear lift movement if necessary, this results in considerably greater flexibility with regard to the stairs to be climbed.
According to a first variant of this, a mounting system is provided on the stair climber or on the wheelchair; it is equipped with a hinge pin on which the support device is mounted swiveling. Provided between the support device and the mounting device is a braking and blocking device that is controlled by a sensor in such a way that it blocks the support device as soon as the stair climber threatens to topple over the stairway, and releases the support device as long as the stair climber is properly inclined relative to the stairway.
With this construction, under normal circumstances the support device is fully and freely movable relative to the stair climbing device or the object conveyed. In this way, it can be freely adapted to stairways of any steepness or flatness. Flat landings do not cause difficulties either. For conveying on level surfaces, the support device can even be-folded up under the object conveyed, in particular the wheelchair. Only when the stair climber device takes up a position such that there is a danger of tilting over is the hinge of the support device blocked, namely until the operator has brought the stair climbing device back into a safe position.
Devices, preferably support feet made of an elastic, stairway-protecting material attached in the lower end area of the support device, advantageously provide a support action impacting largely vertically on the stepping surface of one of the next steps down when the swinging motion is blocked. It has been shown that the support on the stepping surface of the stairs is far safer and more reliable than support on the front edge of the stairs. The jolt caused when the hinge is blocked is thus optimally intercepted.
As an alternative to this, a continuous creeper band is attached at the free end of the support device. This creeper band is short enough that it only needs to bridge over two stairs. Also, only a single, narrow creeper band is needed in the middle of the stairway so that curve-negotiating characteristics are ensured.
According to a third variant, a turnstile with at least two, preferably three support wheels is attached at the free end of the support device. Constructions of a turnstile and support wheels are already used in stair climbing devices.
According to a fourth variant, a paternoster-like lift mechanism is attached to the support device.
According to an advantageous further development of the invention, there is the possibility for the foot or scissor leg executing a linear lift movement, the creeper belt, the turnstile or the paternoster to be motor-driven, preferably synchronized with the lift mechanism of the stair climber itself. In this case, the object conveyed, in particular the wheelchair, is conveyed up and down the stairs with only minimal vibrations. The operator henceforth only has a guiding function and no longer a holding function. Such stair climbers can thus be operated by less powerful persons. The constantly active braking and blocking system prevents the stair climber from tipping over with the wheelchair and the handicapped person in case of a danger.
According to a first variant, the braking and blocking system consists of a ratchet wheel and a ratchet as a heeling sensor. In this connection, the center of the ratchet wheel is preferably situated in the center of the hinge pin and the ratchet is designed as a pendulum and mounted swinging on the mounting device. As soon as the stair climber tips forward, the ratchet engages the teeth of the ratchet wheel and blocks the hinge. Such a blocking system is mechanically simple and operationally reliable.
In this regard, the ratchet advantageously consists of a low-mass part that quickly engages the ratchet wheel due to its low mass, and a high-mass part that is responsible for maintaining the vertical direction under the action of gravity. Both parts are held together by a spring which, however, is weak enough that it does not delay the ratchet""s rapid engaging in the ratchet wheel.
In this regard, the angle of the ratchet wheel relative to the support device is advantageously adjustable. Shifting of the overall center of gravity brought about by the different dimensions and weights of the stair climber, the wheelchair and the handicapped person are thereby balanced out.
Another variant of the braking and blocking system consists of a lockable tension bar of finite length between the support arm on the one hand and the mounting device or stair climber on the other hand.
According to a third variant, a shoe brake is provided as the braking and blocking system.
According to a fourth variant, a spring band brake is provided as the braking and blocking system. These brakes operate very quickly and reliably and already have the necessary free-wheeling operation.
An electrical coupling or a shoe brake is also suitable.
According to another variant, the braking and blocking system is designed as a lockable cylinder piston unit. This is preferably a cylinder piston unit with an internal fluid circuit and, in the fluid circuit, a check valve controlled by the heeling sensor. Hydraulic oils as well as gases can be considered for the fluid.
According to an advantageous further development of the invention, there is a support spring between the support arm and the mounting plate or stair climber. This support spring must be designed in such a way that it is powerless when the stair climbing device is in the properly inclined position relative to the stairway. If the stair climber leans backward toward the stairway, the spring presses it back into the normal position. If the stair climber tends to tilt dangerously forward, the spring draws it back into the correct position. The support spring thereby relieves the operator""s strength in both cases.
To further relieve the operator and to also be able to convey heavy loads quickly and, above all, safely over the stairway, a drive is provided parallel to the braking and blocking system. This can be an electric motor with gears, a hydraulic cylinder, an electric cylinder or the like. In each case, the drive is controlled contingent upon the differences between the desired values and actual values of the position of the support device relative to the stair climber and/or of the pressure forces of the support device on the stairway.
It is clear that considerable space and weight can be spared if, according to a further development, the drive is integrated into the braking and blocking system.
Several variants of construction are also possible for the lift mechanism of the stair climber itself.
According to a first variant, the lift mechanism essentially comprises a straight-line mechanism, a lifting frame mounted movably on it and at least one flap mounted on the lift frame and able to be swung in and out. A continuous chain with a push lever between the chain and the flap is provided as the drive source for the flap. Support feet of a nonskid, stairway-protecting material on the lower edge of the flap complete the construction.
An electric motor with gears is preferably suitable as the drive source.
According to a second variant, the lift mechanism essentially comprises two continuous chains circling parallel and in paternoster-like manner, at least one foot element on each chain and an electric motor with gears as the drive source, and the foot elements stand on the stairway. Such a construction requires relatively little power, and this clearly relieves the source of electric power carried on the stair climber. There is only little load on the material, such that the overall construction can be designed particularly easily.
The foot elements preferably stand with a rounded edge on the stairway. If the foot elements also have a nonskid, abrasion-proof coating, optimal conditions are obtained.
Safety is obviously optimal when the stair climber is drawn as far as possible into the stair. To ensure this, feelers in the form of contact bars are attached on the rear of the stair climber on the right and left; they are actuated only when the stair climber is standing at the next stair edge upward. Only then is the drive source activated for the next climbing lift.
Other sensors measure the upper and lower end position of the flap, the lift frame or the foot elements. In this way, it is ensured that each lift step, whether up or down the stairs, starts from a defined position of the lift mechanism and ends at a defined position.
The proper process control of all drives, i.e. the lift mechanism on the stair climber, the drive on the support device and, where applicable, the drive between the stair climber and the support device, is best ensured by a microprocessor.

Otto Bock Orthopaedische Industrie Besitz-und Verwaltungs-Kommanditgesellschaft