Patent GB-355732-A (GB)
Title: Improvements in or relating to the manufacture of sheet materials having a basis of cellulose esters or ethers
IPC: B29C48/03
Filed: 1930-05-21
Abstract: Cellulose esters or ethers are rendered fluid by the action of heat in the absence of any substantial amounts of volatile solvents and are flowed on to or otherwise brought into contact with rolls or other moving surfaces adapted to control or preserve the required thickness of the sheet or film.  Volatile solvents are only employed, if at all, in such quantities that they need not be removed from the products.  With commercial cellulose drivatives, which are liable to decompose at temperatures near their melting-points, it is necessary to use small amounts of plasticizers to reduce the melting or softening point, but cellulose esters not made in the presence of sulphuric acid, for instance those made with the help of halides with or without hydrohalogen acid in accordance with Specifications 308,322, 308,323, 309,201, 312,095, 312,096, [all in Class 2 (ii), Cellulose &c.], 342,738, 342,740, and 343,986, may be used either alone or with plasticizers.  Esters made in presence of sulphuric acid may be used if sufficiently freed from this acid; the primary ester may be ripened in two stages by the addition of successive quantities of water.  As cellulose ethers, those made by the processes of Specifications 164,374, 164,375, 164,377, and 187,639, [all in Class 2 (ii), Cellulose &c.], are particularly suitable.  The plasticizer may be a sulphonamide, sulphonanilide or other sulphonarylide, alkyl phthalate, organic phosphate such as tricresyl or triphenyl phosphate preferably in conjunction with sulphonamides or other plasticizers readily soluble in the cellulose derivative, triacetin, or sulphonic acid ester, in the proportion of from less than 10 to 50 per cent of the cellulose base. Inflammability-reducing agents may be added, for instance minerals such as phosphates, or preferably agents soluble in the cellulose base, such as halogenated compounds, for instance halogenated aromatic amines and their acidyl derivatives, e.g. trichlormethyl-acetanilide and tetrachlorethyl acetanilide; the brominated compounds of Specification 319,073, [Class 2 (ii), Cellulose &c.], for instance 2.4.6-tribromdiacetanilide, are preferred.  These halogen compounds may be used as the sole plasticizing agents or in conjunction with sulphonamides or the like. Small quantities of dicyandiamide or other agents for taking up any halogen liberated may be incorporated.  In addition to or in place of plasticizers may be used liquids which are solvents for the base at high temperatures and are non-solvents and non-solutes in the cold, for instance various glycols, glycerine and its mono-methyl or monoethyl esters, and other polyhydric alcohols.  Thus the base with or without plasticizers may be dissolved in 1 to 4 times its weight of glycerine at 150-190 DEG  C., or in similar amounts of glycol at 120-180 DEG  C.; the liquid separates almost completely on cooling. Incorporation of the plasticizer &c. with the base may be carried out as described in Specifications 354,860 and 354,861, [both in Group V]; for instance the disintegrated base may be treated with a solution of the plasticizer in a liquid such as ether which is afterwards evaporated and the mass worked; or the base may be sprayed with the plasticizer, with or without ether &c. which is evaporated simultaneously or subsequently.  Or water, with or without organic solvents or diluents, may be employed for obtaining a uniform distribution of the plasticizer within the base.  The base with the plasticizer may again be reduced to a fine powder. Natural or synthetic resins may be added, and fillers may be employed up to 3-4 times the weight of the cellulosic base; substances are preferred which are soluble in or compatible with the base, so as not to destroy the transparency of the products. Pigments or dyes may be added for producing coloured sheets, or discoloration may be corrected by a blue or blue-violet dye, such as 1-methylamino-4-hydroxyanthraquinone or 1.2 p dioxy-5.8-diaminoanthraquinone.  In one form of apparatus, the prepared material is fed, for instance automatically, into a cylindrical tank 6, Fig. 1, provided with steampipes 4 and a stirrer, and optionally with baffles.  The molten material flows over a partition into a compartment 8, in which is a separate heating coil thermostatically controlled, and thence between steam-heated lips 9, a sliding door 11 being lowered to interrupt the flow when required. Heating of the lips 9 may be thermostatically controlled.  From the lips 9, which preferably give a streamline flow, the material passes between hollow adjustable rolls 13, 14 and then over three hollow rolls 16, 17, 18 on to a conveyer 26; the rolls 16, 17, 18 are carried by a frame pivoted about the axis of the last roll, so that the angle of contact of the sheet with the series of rolls may be adjusted, or the rolls swung out of action.  The band of material ejected from the heating tank may be of the final thickness required, or slightly more, but preferably the thickness is reduced by one or more sets of rolls, which may be heated or cooled.  To allow cooling and conditioning of the sheet of material, the conveyer 26, Figs. 1 and 1a, is perforated or of grid form.  The conveyer traverses the lower compartment of a conditioning chamber 25.  In the upper compartment air from a blower 28 is brought to the required temperature and humidity by steam heating pipes and steam jets, and then passes through the lower compartment in counter-current to the sheet.  Other treating agents may be employed, for instance air containing vapour, preferably unsaturated, of solvents such as acetone, benzene-alcohol, tetrachlorethane, or methyl or ethyl formate, or of non-solvents such as benzene, methyl or ethyl alcohol, or diethyl ketone.  If the liquid constituent of the sheet material is sufficiently hygroscopic, ordinary air may be sufficient.  A final adjustment of the thickness of the sheet may be made by rolls 36.  In another form of apparatus, the molten material is drawn up between rolls 42, Fig. 2, partly immersed in the material, and is guided by hollow rolls 45 on to a large bending roller 46, both pairs of rolls serving to cool and reduce the thickness of the sheet. Operation may be begun by means of a piece of flexible material to which the melt can adhere.  In a modification the material is drawn up from the melt by rolls immediately above a slit which may be adjustable, and may be constituted by pivoted jaws within the liquid.  In another form two watercooled rolls are placed adjacent a hole in the side of the tank. Fig. 5 shows adjustable steam-heated jaws 64 and adjustable rolls 72 immediately below a hole in the bottom of the tank, which may be closed by a sliding door 66.  In Fig. 6 the material issues laterally through an aperture over which is a pivoted steam-heated door 74, adjustable by a screw 78.  In another form the liquid, preferably containing glycols, glycerine, or the like, flows over a steam-heated weir and down an inclined surface, being kept hot by a hood, on to a large roll and between this and a small roll.  When liquids are used which are only solvents at high temperatures, the sheet may be carried between 4 or 5 pairs of rollers and maintained for some time at 50-100 DEG  C., to allow the liquid to escape.  In order to avoid undue strains in rolling out the band to the required width, the material may be delivered from the tank in a series of bands spaced apart along the rolls, which then unite them to a single sheet.  The sheet may be stretched by a series of rollers run at different speeds.  Polishing may be effected by buffing or by hot surfaces, or a mat finish imparted by sandblasted surfaces. Engraved rollers may be employed for embossing the sheet.  Metal may be sprayed on, for instance by Schoop pistols.  The sheets may be cut up by circumferential and longitudinal knives on a pair of rollers 79, Fig. 6, and the pieces delivered into a synchronized rack conveyer 80, which may pass through a conditioning chamber. Cut sheets may be delivered between two glass sheets coated with adhesive material such as gelatine, cellulose nitrate or ethers or synthetic resins, as in Specification 326,520, [Class 140, Waterproof &c. fabrics], or a single sheet of glass may be placed between two of the plastic sheets.  Or the glass sheets may be placed above and below the travelling sheet and pressed thereon, the plastic sheet being then cut and its projecting edges softened and used as a seal.  Two or more cellulosic sheets may be united, in some cases with a white or coloured fabric, or wire netting or suspended metal between them. Such laminated products may be used for gramophone records. Specifications 174,660 and 179,208, [both in Class 2 (ii), Cellulose &c.], also are referred to.