Patent GB-1014791-A (GB)
Title: Process and apparatus for casting a synthetic resin film
IPC: B29C48/08
Filed: 1964-01-31
Abstract: 1,014,791. Coated fabrics. UNITED STATES RUBBER CO. Jan. 31, 1964 [April 19, 1963], No. 4114/64. Heading B2E. [Also in Division B5] A solvent-free mixture 15 comprising a liquid room temperature curing resin of short gel life and a cross-linker therefor is poured immediately after its preparation and conversion into a liquid gel through a spout 11, Fig. 1, between the release surfaces of a pair of non-metallic, non-elastomeric carrier webs 13 where it lies to form a bank or reserve 14 of mixture which is taken through the nip rolls 16 by the carrier webs 13 between which at least one layer of fabric is introduced, Fig. 3, and becomes sandwiched between the carrier webs, to produce a fabric containing film having substantially resin free fibres encapsulated by the resin. The resin mixture is preferably poured on to a carrier web 13 from a stationary wide mouth spout covering the width of the carrier between end guards, but may alternatively be poured from a narrow mouth spout which travels back and forth over the width of the carrier between end guards. As the sticky gelled resin mixture 15 is forced to pass under pressure through the calibrated nip of the rolls 16 it liquefies sufficiently to spread over the width of the carrier webs 13 between end guards 17 to form a thin continuous film, the two carrier webs and the film constituting a sandwich or laminate. This is drawn forward by means of a tension controlled (braked) rotating drum 20 having a diameter of, for example, 4 or 5 feet. The drum is preferably removable when full so that it may be replaced by an empty drum and the process of sandwich formation continued while the film is curing on the original drum in a convenient location. The nip rolls 16 and the supply rolls 12 for the carrier webs 13 may be idler rolls or driven metering rolls geared or braked to co-operate with the take-up roll 20. After about an hour the film is sufficiently cured to be separated from the carrier webs by driving the carrier web rolls 12 in a direction opposite to that in which they turned during the film forming operation. The carrier webs are thereby rewound on the carrier web rolls ready for future use and the film is either used directly or wound up on a film roll which may then be stored until the cure is complete. The short gel life of the resin mixtures used in this invention allows the production of films having differently coloured stripes running the length thereof. These stripes are formed by pouring differently coloured resin mixtures at predetermined intervals along the width of the carriers, each differently coloured resin mixture emerging from a different spout and the banks of the mixtures at the inlet side of the roll nip being separated by dividers similar to the end guards 17. The mixtures are sufficiently viscous by the time they pass the dividers that there is little or no mingling of the colours during the passage of the mixtures through the nip or thereafter. The carrier webs may consist of paper or a plastic such as polytetrafluoroethylene, vinylidene chloride, polyvinyl chloride, polypropylene, polyethylene, or polyethylene terephthalate. The carrier webs must present to the film a release surface which may be a property of the carrier itself or may be applied to the operative surface of the carrier as a release agent, such as one of the above listed plastics. The short gel or pot life resins used, after being mixed with a crosslinker or with a mixture of a crosslinker and an appropriate accelerator, gel rapidly (e.g. within 15 and usually within 5 minutes) to form sticky, partially cured, viscous semi-liquids which are capable of being spread into thin films by moderate pressures and have sufficient viscosity to remain in the form of thin films while solidifying. Preferred resins are polyurethane prepolymers (isocyanate-terminated polyethers or isocyanate-terminated polyesters), polysulphide or "Thiokol" resins, organo-polysiloxane resins and polyepoxide resins. The resin is preferably thermosetting and the most preferred resins are polyurethane prepolymers. These and the polyepoxide resins are conventionally cured by diamines such as 4,4<SP>1</SP>- methylene-bis-2-chloroaniline, dichlorobenzidine or any of the polyols. A small proportion of an accelerator such as oxalic or stearic acid may be present in the resin mixture. The process of the invention is preferably performed in the absence of heating or cooling. As shown in Fig. 3, the layer of fabric 31, e.g. open weave nylon, is introduced from a fabric supply roll 30 between nip rolls 16 and drawn along past the bank 14 with and between the carrier webs 13 by the take-up drum 20. The fabric 31 thereby becomes a part of the mixture 15 which is sandwiched between the carrier webs. The viscosity of the resin mixture, the pressure applied by the nip rolls, and the composition, weave and porosity of the fabric may be selected to produce resin layers of any desired thickness on either or both surfaces of the fabric. If the weave of the fabric is very close, resin may be introduced on each side of the fabric by spouts 11 located on each side of the fabric. If the weave of the fabric is very open and it is desired to have resin on both sides of the fabric, it is preferred to coat each side of the fabric in a separate pass through the nip rolls 16 to avoid the entrainment of air bubbles within the interstices of the weave. Two or more layers of fabric may be introduced from one or more fabric rolls. The fabric layers may be kept in close contact prior to their introduction into the nip, or may be separated prior to their introduction into the nip so that there is produced a laminate composed of the following layers: resin, resin-encapsulated fabric, resin, resin-encapsulated fabric and resin. In the preparation of such a laminate an additional resin pouring spout 11 between the layers of fabric may be used advantageously. Because no solvent is present in the resin mixture, the fibres of the fabric do not become impregnated with resin and consequently retain their strength and flexibility. During the removal of the sandwich composed of carrier webs, resin and fabric from the take-up drum 20, the direction of rotation of the fabric roll 30 may be reversed so that the film consisting of fabric encapsulated by cured resin is woundup on the fabric roll 30, just as the carrier webs 13 are simultaneously wound on their respective supply rolls 12.