Mold having a thin release coat

Abstract: A mold for casting articles, said mold having inner surfaces coated with a release coating consisting essentially of polymerized amphiphilic molecules that are capable of self-assembly and that are self-assembled on said surfaces.

Description: Technical Field This application relates to the art of coating compositions, and to molds with surfaces having improved coatings thereon. The invention is particularly applicable to ultra thin films formed by amphiphilic molecules. Background Art Compositions having ingredients that are capable of forming thin films on substrates are discussed in an article entitled Oleophobic Monolayers, by W. C. Bigelow et al., J. Colloid Sci. I, pages 513-538 (1946); in an article entitled Wettability and Conformation of Reactive Polysiloxanes, by Lieng-Huang Lee, Journal of Colloid and Interface Science, Vol. 27, No. 4, August 1968, pages 751-760; in an article entitled Electrical Conduction Through Absorbed Monolayers, by E. E. Polymeropoulos et al., J. Chem. Phys. 69(5), Sept. 1, 1978, pages 1836-1847; and in U.S. Patent No. 4,539,061 issued September 3, 1985, to Jacob Sagiv, for a Process for the Production of Built-Up Films by the Stepwise Adsorption of Individual Monolayers. These compositions use thin solvents in which a film forming substance is soluble. In general, the solvents are toxic and environmentally unsafe. Highly liquid compositions also lose their usefulness very rapidly when exposed to airborne moisture and/or oxygen. Highly reactive materials tend to form molecular agglomerations and precipitate out of solution. Release coatings comprising three layers, wherein the second layer is a siloxane film made from amphiphilic molecules, are known from EP-A-0 482 613. It would be desirable to have a film forming composition that is not noxious or hazardous to persons or the environment, and that would provide optimum protection and stability for a film forming substance in the composition. At the same time, it would be desirable to provide such a composition that is easily applied to substrate surfaces to form a substantially continuous ultra thin film of substantially uniform thickness thereon. Molds for casting optical lenses are usually provided with a release coating for allowing a cast lens to be easily separated from the mold without damaging the surface of the cast lens. The mold must be thoroughly cleaned and provided with a new release coating for each lens that is cast. It would be desirable to provide a mold with a release coating that could be used for casting a plurality of lens or other articles, and that would require minimal cleaning before being ready for reuse. We have now found it possible to provide an improved coating composition and method for providing ultra thin films on substrate surfaces; to provide a coating composition having a substantially neutral carrier that is environmentally safe and non-toxic to persons; to provide an improved coating composition and method for forming ultra thin films in a manner that does not release hazardous materials to the environment, or create a noxious or hazardous environment for workers; to provide a coating composition containing a film forming substance that is very stable and resistant to deterioration, while being very reactive for film formation; to provide a coating composition having an extremely low moisture content and a very low affinity for moisture; to provide a coating composition that inhibits diffusion of moisture into the composition to thereby minimize deterioration of a film forming substance within the composition; to provide improved substrate surfaces, such as on glass, ceramic and porcelain cookware, laboratory ware, glass and plastic eyeware lenses, and molds made from or lined with glass, porcelain or chrome; to provide a commercially cost effective composition and method for modifying surface properties of substrates by forming substantially continuous ultra thin films of substantially uniform thickness thereon; and to provide an improved mold for casting optical lenses. Statement of the Invention According to the present invention there is provided a mold for casting articles and having inner mold surfaces coated with a hydrophobic release film of polymerized amphiphilic molecules having a thickness not greater than 10 nanometers, said amphiphilic molecules being self-assembled and self-attached by chemically bonding to said mold surface, said amphiphilic molecules being derived from a film forming substance having the general formula RmSiXn where R is one or more of a substituted silane, a substituted siloxane, an apolar alkyl group, an apolar alkyl ether group, an apolar fluorinated alkyl group, or an apolar fluorinated alkyl ether group, the said groups having 6-30 carbon atoms, where m plus n equal four, and where X is selected from halogens, hydroxy and alkoxy. Film forming substances used in the compositions of the present application are capable of forming films and attaching to substrates by reactions and forces of the type discussed in the aforementioned articles by Bigelow et al , L.H. Lee, E.E. Polymeropoulos et al , and J. Sagiv. The film is chemically bound to a surface on which it forms. To prepare the mold of the present invention, the mold is coated with a film forming substance capable of forming a substantially continuous ultra thin film of substantially uniform thickness. The film forming substance may be dispersed in an aqueous carrier. In the present application, amphiphilic molecules form an ultra thin substantially continuous film of substantially uniform thickness, and attach to a substrate surface. In the most preferred arrangement of the present application, the film forming substance consists essentially of amphiphilic molecules. That is, the film formed on a surface using the composition of the present application is formed solely from amphiphilic molecules in the composition. Film formed for use in accordance with the present application is characterized by its substantially uniform thickness not greater than 10 nanometers. Compositions used in the present application have a preferable consistency range at 25°C of 35-400 by the cone penetration test. However, a lower consistency can be used, and the consistency is preferably not greater than 400 at 25°C. The preferred melting point is higher than 30°C, and most preferably higher than 50°C. A preferred melting point range is 30-80°C, although higher melting points can be used by preheating the composition and/or the substrate to which it is applied. Lower melting point compositions are preferred for ease of application, and minimize or eliminate the need to preheat the composition and/or substrate. Compositions used in the present application can employ up to 0.5% by weight of a catalyst, such as zinc chloride, aluminum chloride or mineral acids, to enhance film formation. Compositions used in the present application can employ up to 0.5% by weight of a quencher, such as one or more of amines, aluminum and zinc powder, and metal carbonates for reaction with noxious fumes. For example, if the composition uses materials that react to form acid fumes, the quencher will neutralize the acid fumes by forming a salt. In the present invention the compositions are used on internal surfaces of molds, preferably molds for casting optical lenses of plastic materials. Compositions used in the present application can change the surface energy of surfaces to which they are applied. Preferred films formed in accordance with the present application are substantially invisible unless a dye is added to the composition or incorporated in the amphiphile. The composition used in the present application is applied to a substrate surface, and a substantially continuous ultra thin film of substantially uniform thickness is allowed to form from the amphiphilic molecules in the film forming substance. The molecules also attach themselves to the substrate surface by various forces and bonds as discussed in the aforementioned articles, and are primarily chemically bound to the surface. Subsequently, the excess material is washed away, such as with soap and water. A substantially continuous ultra thin film of substantially uniform thickness remains on the substrate surface, and provides excellent abrasion and stain resistance, along with excellent release properties. The properties imparted to the substrate surface by the film can be varied by selecting different film forming substances. The mold of the present application having a substantially continuous ultra thin film of substantially uniform thickness coated on a substrate surface is essentially prepared in three steps. First, a film forming substance is provided, which may be in the form of a homogeneous coating composition made by dispersing the film forming substance in an aqueous carrier. Small quantities of one or both of a catalyst and quencher may be included. Second, the film forming substance is applied to a substrate surface. Third, the amphiphilic molecules in the film forming substance are allowed to form a substantially continuous ultra thin film of substantially uniform thickness that attaches to the substrate surface. Film forming substances containing polymerizable moieties may be polymerized by heating, photochemical reaction and/or use of a catalyst. Excess coating material is then washed away. Brief Description of the Drawings Figure 1 is a partial side elevational view showing a film forming composition spread on a surface; Figure 2 is a partial cross-elevational view of a surface having a film thereon in accordance with the present application; Figure 3 is a top plan view of a mold for molding optical lenses; and Figure 4 is a cross-sectional elevational view taken generally on lines 4-4 of Figure 3. As used in this application, a film forming substance is one containing amphiphilic molecules that are capable of forming a substantially continuous ultra thin film of substantially uniform thickness on a substrate surface. In this application, a substantially continuous film is one that is substantially unbroken except for the presence of relatively minor defects or imperfections such as pin holes. An amphiphile contains a polar region and a non-polar or apolar region. The non-polar or apolar component typically consists mainly of alkyl and alkyl ethers or fluorinated alkyls or alkyl ethers. These apolar regions may include diacetylene, vinyl-unsaturated, or fused linear or branched aromatic moieties. In addition the apolar region may contain organic dyes with or without metal, such as pthalocyanines, porphyrins and phenol blues. The film forming substance consists essentially of RmSiXn where the non-polar R is an alkyl or alkyl ether or fluorinated alkyl or alkyl ether group of 6-30, and most preferably 12-30, carbon atoms long. The film forming substance, and particularly the alkyl or fluorinated alkyl group, may include one or more of polymerizable moieties, dyes or dipoles. In the above formula, X is selected from halogens, hydroxy and alkoxy. In the formula m plus n equal 4. In still another preferred arrangement, R may be a substituted silane or siloxane. Obviously, the film forming substance can be a mixture of a plurality of different types of RmSiXn in any proportion, such as one where R is 10, one where R is 12 and one where R is 14. These can be mixed in various amounts, such as, by way of example only, 30% where R is 10, 50% where R is 12 and 20% where R is 14. The film forming substance may be thoroughly mixed and uniformly dispersed in an aqueous carrier to provide a substantially homogeneous composition. A small quantity of a catalyst may be uniformly mixed with the film forming substance to enhance film formation. For example, up to 0.5% by weight of one or more of zinc or aluminum chloride or mineral acids may be added. A small quantity of a quencher may also be added to the composition for neutralizing any acid fumes that may be generated during film formation. For example, up to 0.5% by weight of one or more of an amine, aluminum or zinc powder, or metal carbonates may be added to the composition as a quencher that will neutralize acid fumes by forming a salt. When more than one quencher is used, the total amount of quencher material is not more than 0.5% by weight of the entire composition, and the same relationship is used for the catalyst. The film forming substance and composition used in the present application have a preferred consistency or firmness as determined by a cone penetration test. Examples of consistency will be given as determined by ASTM designation D937-87 approved October 30, 1987, and published in December 1987. The film forming substance and composition used in the present application preferably have a consistency at 25°C that is in the range of 35-400, although a lower consistency can be used when the substrate and/or composition is heated before application of same to a surface. In the cone preparation test for consistency, higher numbers mean that the material is softer because the cone penetrates further. Thus, a material having a consistency of 35 is much firmer and resistant to penetration than a material having a consistency of 400. The consistency of the film forming substance and composition is preferably less than 400. A more preferable range is 150-300. The preferred melting point of the film forming substance and composition is higher than 30°C, and most preferably higher than 50°C. A preferred melting point range is 30-80°C, although higher melting points can be used by heating the film forming substance and composition and/or substrate. Lower melting points are preferably for ease of application of the composition to a surface, while eliminating or minimizing the need to preheat the composition and/or substrate. The melting point may be determined in accordance with ASTM designation D127. The film forming substance and composition used in the present application can be applied to substrate surfaces in any suitable manner, such as by wiping, brushing, rolling, spraying, dipping or the use of a doctor blade. The film forming substance and composition can also be foamed as it is applied to a substrate surface or as the mold to be coated with film is passed through the foam. To form a substantially continuous ultra thin film of substantially uniform thickness on a substrate surface, the surface is completely covered with the film forming substance and composition. The film forming substance and composition is allowed to remain on the surface for a sufficient period of time to allow the film to form and attach to the surface. The amount of time required for film formulation and bonding to the surface depends upon the type of substrate, the consistency of the film forming substance and composition, the temperature and the particular film forming substance being used. Where the film forming substance contains a polymerizable group, the film may be cured by either heating or exposure to a light source, preferably an ultraviolet light source. Polymerization can be initiated at anywhere from 20° to 150°C. Heat may be applied by blowing hot air on the surface, by passing the articles through an oven, or by immersing the article in hot water. Polymerization may be effected during a time period up to about 30 minutes. When X in RmSiXn is a halogen, polymerization can be completed in less than one minute and, when a non-halogen, can be substantially completed in up to 30 minutes. Once the film has formed and is attached to the substrate surface, the excess film forming substance and composition is washed away. The excess film forming substance and composition may be removed with a suitable solution, such as soap and water, and then rinsed. A suitable solvent such as mineral oil may also be used to provide an initial rinse for washing away the excess film forming substance and composition. The substrate surface is left with a film having excellent abrasion and stain resistance, along with excellent release properties. The film is substantially invisible unless a dye has been added to the film forming substance and composition or incorporated in the amphiphile. The film forming substance and composition and method used in the present application are particularly advantageous for providing a film of the type described on non-porous substrates, such as glass, plastics, ceramics, porcelain, fiberglass and metals. Film applied in accordance with the present application is relatively permanent in nature, and resists all common household solvents and chemicals, along with food products and cosmetics. The film is hydrophobic, and also has excellent water beading and anti-stick properties. The film is used for a mold release coating. The film is particularly advantageous when applied to inner surfaces of molds used for casting optical lenses of plastic materials. In the arrangement of the present application, the sole material that forms the film in-situ on a substrate surface consists essentially of amphiphilic molecules. That is, the sole material in the finished film consists essentially of amphiphilic molecules from the film forming substance. The film is characterized by its highly uniform thickness of not more than 10 nanometers. The film is advantageous as a release coating on mold surfaces, particularly mold surfaces used in casting optical lenses from such materials as aliphatic polycarbonate and other plastic resins. Figure 1 shows a substrate A having a surface 12 completely covered by a continuous thin coating of composition B used in the present application. Composition B has amphiphilic molecules dispersed therein, and only a few of same are specifically identified by letter C. Each amphiphilic molecule C has a polar end 18 and an opposite non-polar end. The natural environmental atmosphere of the earth always contains some moisture, and objects within such atmosphere also have moisture thereon. Therefore, surface 12 of substrate A has moisture thereon even though it is in such small quantities as to be undiscernable to the eye or touch. Polar ends 18 of amphiphilic molecule C are attracted toward surface 12 and migrate through composition B until they attach to surface 12. Amphiphiles chemically react with hydroxy groups on a glass surface to form a covalent chemical bond. Composition B is simply left on surface 12 for a sufficient period of time to allow enough molecules C to migrate toward and attach to surface 12 and to one another to completely cover surface 12 with a continuous film of molecules C. The amphiphilic molecules normally comprise 0.1-20% by weight of the entire composition B, and more preferably 1-5% by weight of the entire composition B, although larger or smaller amounts can be used. Amphiphilic molecules in the amount of 2% by weight of the entire composition have been used with good results. Obviously, substantially larger amounts by weight of the amphiphilic molecules can be used. However, larger amounts of the amphiphilic molecules are not necessary and it is generally wasteful to provide substantially larger quantities. The amount of time required for the molecules to form a continuous film on surface 12 will vary depending upon the amount of amphiphilic molecules in the composition, the viscosity of the composition, the type of substrate, and the temperature conditions. After passage of sufficient time to form and cure a continuous thin film, composition B is washed from surface 12 as with soap and water to leave a continuous thin film of amphiphilic molecules C bonded thereto and to one another. Figure 2 shows a substrate D having a surface 22 covered with a continuous film E consisting essentially of amphiphilic molecules applied as previously described. A substrate surface to which the film is applied may have some depressions and other irregularities as generally indicated by numerals 24, 25 and 26 in Figure 2. It is believed that film E used in the present application follows the contours of such irregularities as shown in Figure 2 so that the film is of substantially uniform thickness throughout its entire extent. That is, the film is not self-leveling, and is in contrast to films or coating that are self-leveling and completely fill irregularities in a surface so that the coating or film has many areas of different thickness. It is possible that some areas of the substrate surface, particularly microscopic or fissures, may be filled with the molecules so that a greater thickness would exist. Film E seals the pores of the surface to which it is attached. Figure 3 shows a mold assembly G for casting optical lenses using plastic material, such as aliphatic polycarbonate. The mold includes an elastomeric ring H that is deformable and stretchable. As shown in Figure 4, the inner peripheral surface 30 of elastomeric ring H has a pair of axially spaced-apart circumferential grooves 32, 34 therein. A pair of glass molds I, I' have their outer peripheral portions closely received and gripped within grooves 32, 34 in elastomeric ring H. Glass molds I, I' have inner surfaces 40, 40' that are highly polished to an optically flat finish, and are also curved for providing desired predetermined characteristics to a lens cast in the mold. Inner surfaces 40, 40' are provided with a continuous thin film E, E' of amphiphilic molecules in accordance with the present application. The film is formed on surfaces 40, 40' before assembling glass molds I, I' to ring H. A radial hole 50 in elastomeric ring H located intermediate axially spaced-apart glass molds I, I' is provided for filling the mold cavity with plastic material. The mold cavity between inner surfaces 40, 40' of glass molds I, I' is completely filled with the plastic material, and the entire mold assembly is then submerged in a hot water bath at a temperature of 60°-180°C for about 1-24 hours. This polymerizes the plastic used to cast the lens. The mold assembly is then cooled, and the elastomeric ring H is severed and separated from the glass molds and the cast lens. The glass molds are then separated from the cast lens. The inner surfaces of the glass molds having the release coating of film E thereon are then mildly cleaned and assembled with a new elastomeric ring H for use in casting additional lenses. The release coating provided by film E eventually deteriorates due to oxidation and abrasion but can be reused as a release coating to cast not less than 10 lenses and preferably more than 20 lenses before renewal of the release coating is necessary. Thus, film E minimizes the amount of cleaning necessary before the mold can be reused, and the release coating does not have to be renewed after each lens is cast. A composition useful in the present application consists essentially of a film forming substance and an aqueous carrier for the film forming substance. The film forming substance and composition may include extremely small amounts of non-essential ingredients such as a catalyst, a quencher or a dye. The film forming substance, which may be dispersed in the aqueous carrier, consists essentially of polymerizable amphiphilic molecules that automatically separate from and migrate through the carrier and self-assemble into a substantially continuous film of substantially uniform thickness not greater than 10 nanometers. The film chemically bonds to surfaces on which it forms. The remainder of the film forming substance and composition is readily removable and washable from a surface to which it is applied so that only the thin film remains on the surface. The film forming substance and composition used in the present application is particularly characterized by the absence of any solid particulate materials that would make it impossible to allow a film to form on a surface in a continuous coating of substantially uniform thickness. When applied to a mold surface, the film of the present application has a substantially uniform thickness not greater than about 10 nanometers. It is particularly advantageous to apply the film of the present application to mold surfaces of glass, ceramic, porcelain or chrome. However, it will be appreciated that such a film can be applied to a mold of other materials. When it is desired to renew the coating, heat and/or a strong base solution, such as sodium hydroxide, may be used to remove all of the original coating. The surface is then washed, dried and a new coating applied thereto for forming a new film thereon.

Claims: A mold for casting articles and having inner mold surfaces coated with a hydrophobic release film of polymerized amphiphilic molecules having a thickness not greater than 10 nanometers, said amphiphilic molecules being self-assembled and self-attached by chemically bonding to said mold surface, said amphiphilic molecules being derived from a film forming substance having the general formula RmSiXn where R is one or more of a substituted silane, a substituted siloxane, an apolar alkyl group, an apolar alkyl ether group, an apolar fluorinated alkyl group, or an apolar fluorinated alkyl ether group, the said groups having 6-30 carbon atoms, where m plus n equal four, and where X is selected from halogens, hydroxy and alkoxy. The mold of claim 1 wherein R includes one ore more polymerizable moieties, dyes or dipoles. The mold of claim 1 wherein R includes one or more of diacetylene, vinyl-unsaturated, or fused linear or branched aromatic moieties. The mold of claim 1 wherein the hydrophobic release film contains a catalyst and/or quencher. The mold of claim 1 wherein said mold surfaces are highly polished to an optically flat finish. The mold of claim 1 wherein said mold is of a material selected from glass, ceramic, porcelain and chrome. The mold of claim 1 wherein said mold has separable parts that include a pair of spaced-apart generally opposite glass molds having curved inner surfaces with said release film of amphiphilic molecules thereon. The mold of claim 7 wherein said mold parts include an elastic peripheral ring for separably holding said glass molds in predetermined spaced-apart relationship.

Inventors: SINGH BRIJ P, SUBRAMANIAM RAJ, SINGH, BRIJ P., SUBRAMANIAM, RAJ
Applicants: NANOFILM LTD, NANOFILM, LTD.
Application year: 1991
Main classification: C09D5
IPC codes: C09D4, C03C17, B05D1