GB1021310A - Improvements in coating method and apparatus - Google Patents

Abstract

1,021,310. Web coating apparatus. CHAMPION PAPER CO. Ltd. June 2, 1964 [Oct. 30,1963 ], No. 22790/64. Heading D1L. A moving web of material is coated with a fluid coating by supplying coating material to a point adjacent the web, applying a portion of the coating directly to the web, removing a further portion of the supplied coating, subjecting the removed coating to a frictional grinding to reduce agglomerates and contaminating constituents therein, and returning the further portion of the coating to the point of application adjacent the web. In one embodiment, Fig. 1, the web W passes in contact with a driven applicator roll 1 and upwardly over a guide roll 3 to a nip formed between a press roll 5 and a heated casting drum 7. The lower portion of the roll 1 is immersed in a pool of coating C in a pan 9. Excess coating carried to the nip between the roll 5 and the drum 7 is returned to the pool C by a baffle 11. Coating from a preparation system S is pumped or flows into a supply line 13 which discharges into a "closed loop" system 10 which comprises a line 21, a pump 23, a line 25, grinding means 30, a line 29, a distribution trough 31 formed integrally with the pan 9, the pan 9 and a line 33. The line 13 is provided with a regulatory valve 15. Immediately upstream of the juncture of the line 13 with the system 10 is a dilutent supply line 17 provided with a regulatory valve 19. The valves 15, 19 may be manually controlled or monitored automatically via an automatic control which may comprise a strain gauge to measure by weight the coating in the pan 9 and to regulate both coating and dilutent supply to the system 10 in response to the measured weight. The variable speed pump 23 receives at its inlet side fresh coating from the line 13 and coating from the pan 9 and discharges coating to the means 30 comprising an attrition mill. Coating supplied to the trough 31 flows over a weir 32 into the pan 9 so as to prevent foaming and undue agitation of the coating in the pan 9. The attrition mill 30, Fig. 3, comprises a frustro-conical grinding tank 47 surrounded by a jacket 50 through which a suitable fluid cooling medium is circulated. The tank 47 is filled with spherical grinding elements 63 formed of a suitable hard material, e.g. steel or ceramic material. An agitator comprises a vertical shaft 65 driven by a motor E and provided with vanes 67 varying in length so that their terminals are uniformly spaced from the tank 47 throughout its interior. The coating introduced into the tank 47 via an inlet 49 intermingles with and is crushed and pulverized by the spheres 63. The ground coating passes through a screen 59 into a collection manifold 55 and thence through an outlet 61 into the line 29. In a further embodiment, Fig. 2 (not shbwn), the web W extends over an applicator roll 1<SP>1</SP> dipping in a coating in a pan 9<SP>1</SP> which is extended to support a blade B forming a nip with a back-up roll R, the blade B doctoring excess coating from the web W. Fresh coating is not fed directly into the "loop" system, comprising a pump 23<SP>1</SP>, a line 25<SP>1</SP>, an attrition mill 30<SP>1</SP>, a line 29<SP>1</SP>, a trough 31<SP>1</SP>, the pan 9<SP>1</SP> and a line 331, but is fed via a pump 73 and a line 71 through an attrition mill 40 directly into the trough 31<SP>1</SP>. In another embodiment, Fig. 5 (not shown), a driven applicator roll 79 rotates in a coating pan 75 in which a weir 85 is formed to divide the pan from a distribution trough 87 the trailing edge of which is extended upwardly at 89 and has fixed thereto a baffle 91. A doctor blade 100 in the form of a rotating blade, trailing blade or bull-nose blade is mounted on the baffle 91. A back-up roll (not shown) may be provided. The bottom of the pan 75 slopes from one end wall 77 toward the other end wall 77<SP>1</SP>, Fig. 4 (not shown), and is provided with a drain opening 93 covered with a perforated cover 95 and communicating with a housing 97 forming the jacket of an attrition mill 110. The latter comprises a driven shaft 101, Fig. 4 (not shown), carrying radially extending vanes 109 along the length thereof and spherical grinding elements 111 being provided. The coating from the pan 75 enters the mill 110 through the opening 93 and flows horizontally along the length of the mill and passes through an outlet 113 to a pump 115 which returns the coating through a conduit 119 to the trough 87. Fresh coating enters the mill 110 through an inlet 123 and mixes with the recirculated coating therein. A level sensing float 131 in the pan 75 generates signals to control valves 130, 133 controlling the supply of fresh coating and dilutent, respectively. A temperature control chamber 137 surrounds the bottom of the pan 75 and a major part of the housing 97 and a coolant or heating fluid may be circulated therethrough. The invention is applicable to a coating machine having an air-knife doctor or to a machine in which the coating is sprayed on to the web. The coating may be applied to a paper web at a stage in the paper machine or may be applied as a separate operation. The coating may be an aqueous base, mineral pigment, adhesive coating, e.g. a clay or casein coating to which defoaming agents, wetting agents, setting agents solvents and dyestuffs may be added.