Patent GB-347647-A (GB)
Title: Manufacture of artificial and compound sheets
IPC: C03C27/10
Filed: 1929-10-21
Abstract: Cellulose or cellulose derivative sheets having a thickness greater than ,005" particularly sheets between ,01" and ,03" thick for use in the manufacture of laminated glass are made by coating a surface with a solution of cellulose or of cellulose derivative and evaporating the solvent from the coating. The sheets may be finally stripped from the surface if desired and may consist of reconstituted cellulose made from viscose or of inorganic derivatives of cellulose such as the nitrate, or of cellulose esters such as the acetate, formate, propionate or butyrate or of cellulose ethers such as ethyl, methyl, and benzyl cellulose.  The volatile solvents for making the solution may comprise one or more of the following:-acetone, benzene, ethyl acetate, methylene chloride, ethylene dichloride, ethyl alcohol, methyl alcohol, chloroform.  The solutions are preferably filtered through fine cloth, paper, &c. or a number of filtrations through the same or different media may be made.  Substances such as carbon black, silica gel, fuller's earth, &c., to aid filtration or absorb colour may be added to the solutions, or the impurities may be removed by centrifuging.  The solutions may contain plasticizers such as triacetin, diethyl tartrate, dibutyl tartrate, diethyl phthalate, and diphenylol propane, or medium boiling solvents such as ethyl lactate, or high boiling solvents such as diacetone alcohol.  Resins such as fusible and soluble phenol aldehyde resins prepared in the presence of an acid catalyst, diphenylol propane aldehyde resins, diphenyl ketone resins, toluene sulphonamide aldehyde resins, or stabilizers such as urea and dyes and/or pigments may also be added. The solution is applied to smooth surface such as glass or polished nickel by brushing, spraying, flowing or dipping.  The sheet may either be made from a single coating or it may be built upon the surface by applying successive coatings and each coat may be dried to any extent before applying the next coat.  The surfaces to be coated may be carried by a conveyer under a spraying, flowing or brushing device.  For making laminated glass the sheets may be separately made, then inserted between glass sheets previously coated with adhesive and finally heated and pressed.  Alternatively, the solution of cellulosic material may be applied directly to the adhesive coated glass.  Two or more sheets of cellulose material may be coated with adhesive and pressed to form a thicker sheet. The adhesive applied to the glass may consist of gelatine or a polymerized vinyl compound or the synthetic resins mentioned above may be employed.  Preferably esters or ethers of cellulose are incorporated in the adhesive.  In some cases an adhesive coated glass sheet may have four or five layers of coating composition each layer being approximately ,002" thick.  In one modification, the solutions for the different coatings may be of different compositions.  The special adhesive coating for the glass may be dispensed with and the first coating for the plastic sheet may be such as to give good adherence to glass while subsequently progressively harder coatings are employed until the centre of the plastic sheet is reached after which the coatings are applied in reverse order.  The sheets may be built up of more than one cellulose derivative.  Thus the outer layers may be cellulose nitrate and the inner layers cellulose acetate, or, if the sheet is built up on glass, the coating adjacent the glass may be cellulose nitrate and the central layers cellulose acetate. The proportion of resins in the different coatings may also be varied.  In some cases, if colouring matter is to be added it may be incorporated in a material such as cellulose nitrate in which it is stable, while the remaining layers may consist of cellulose acetate without colouring matter.  For making translucent but non-transparent glass one opaque or semi-opaque layer may be incorporated in the sheet, or decorative effects in coloured lacquer may be produced in the centre of the sheet.  In another modification, composite sheet of alternate layers of cellulose derivative and adhesive may be built up, and such a composite sheet may be mounted between adhesive coated glass sheets for making laminated glass.  In another example, two glass sheets may be coated on one side with successive layers of cellulose acetate until a sheet ,01" thick has been built up, the coated surfaces being then placed together and the assembly heated and pressed.  Or one of the glass sheets may be coated with adhesive and the other have a cellulosic layer of ,02" thickness built up on it to form a safety glass assembly.  The cellulose derivatives may be bleached with oxidizing-agents.  In some cases, evaporation of the solvent may be retarded to prevent crinkling of the layers, by placing the coated surface in a confined space within a container or by passing the coated sheets on a conveyer through an unventilated tunnel.  The container may be provided with openings to permit the introduction of acetone vapour or other vapours during the drying or the containers may be cooled by water.  In one example a solution of 20 parts of cellulose acetate and 80 parts of acetone is flowed on to a glass sheet to form a layer ,2" thick, the sheet is then placed in an airtight shallow container saturated, if desired, with acetone vapour for 2-3 hours and the container then apertured to allow the escape of the solvents so that the sheet dries in 12-24 hours.  The drying is completed in an oven.  Suitable solutions giving parts by weight for forming a sheet exceeding ,01" in thickness are (a) cellulose acetate 10 parts, acetone 40 parts, plasticizer, such as triacetin, diethyl phthalate, diphenylol propane 6 parts; (b) cellulose acetate 10 parts, acetone 20 parts, benzene 10 parts. If desired 10 parts of diacetone alcohol or ethyl lactate may be added; (c) cellulose acetate 10 parts, synthetic resin 2,5 parts, acetone 20 parts.  The resin may be diphenylol propane formaldehyde resin, phenol formaldehyde resin prepared in the presence of an acid catalyst, or toluene sulphonamide formaldehyde resin.  The cellulose acetate may be replaced by the nitrate.  Examples of solutions for making a reinforcing layer on adhesive coated glass are (a) cellulose acetate 20 parts, acetone 100 parts.  Instead of cellulose acetate the propionate or butyrate may be used.  (b) cellulose acetate or nitrate 20 parts, triacetin 10 parts, acetone 100 parts; (c) cellulose acetate 25 parts, triacetin 5 parts, diethyl phthalate 5 parts, acetone 80 parts, benzene 10 parts, ethyl acetate 10 parts, diacetone alcohol 5 parts.  For making a number of layers by spraying or dipping the following solutions may be used; (a) cellulose acetate 10 parts, acetone 50 parts, alcohol 25 parts, benzene 25 parts, diacetone alcohol 15 parts, triacetin 6 parts.  The triacetin may be wholly or in part replaced by diethyl phthalate, diphenylol propane, or mono ethyl xylene sulphonamide, and the diacetone alcohol replaced by ethyl lactate, ethyl oxybutyrate or tetrachlorethane; (b) cellulose nitrate 10 parts, ethyl acetate 25 parts, ethyl alcohol 25 parts, benzene 25 parts, butyl alcohol 20 parts, butyl acetate 20 parts, camphor 4 parts.