GB2235142A

GB2235142A - Coating of substrates

Info

Publication number: GB2235142A
Application number: GB8918181A
Authority: GB
Inventors: Philip Derek Young
Original assignee: Courtaulds PLC; Courtaulds Textiles Holdings Ltd
Current assignee: Courtaulds Textiles Holdings Ltd; Akzo Nobel UK PLC
Priority date: 1989-08-09
Filing date: 1989-08-09
Publication date: 1991-02-27
Anticipated expiration: 2009-08-09
Also published as: GB8918181D0; GB2235142B; DE4024851A1

Abstract

Apparatus for applying a coating material, eg a foamable material, to a substrate 25, which moves past a coating head 20, comprises a holding tank 22 for the coating material, a load cell 23 for weighing the coating material in the tank 22 and a pump 24 for supplying the coating material at a controlled rate from the tank 22 to the coating head 20. The pump 24 is controlled by an electronic control unit 34, which is responsive to a first control signal 30 from the load cell 23 and a second control signal 29 from a tachogenerator 28 measuring the speed of movement of the substrate 25 past the coating head 20. The control unit 34 may also receive a control signal from a sensor 41 representative of the width of the substrate 25 and a reference signal indicative of the desired percentage of solids in the foamed compounds. In this way the desired weight "add on" of coating material can be controlled to a predetermined value. <IMAGE>

Description

1 COATING OF SUBSTRATES This invention relates to apparatus for and a

method of applying a liquid coating material to a substrate. In particular, but not exclusively, the invention relates to the application of a thin coating of foam material to the back of a flexible web material. Typically, for example, used for oroviding a fire retardina the invention can be backing to fabric materials such as those used, for example, in car upholstery and internal finishes of motor cars; for stiffening fabric matOrials, e.g. those used in blinds and for the application of foamed rubber materials and foamed plastics materials to the backs of carpets or other floor coverings.

In all of these applications there is a need to be able to control accurately, not only the amount of coating material but also the density of the coating material as it is applied to a continuously moving web.

In some applications it is necessary to monitor and control very closely the application of a coating material to a moving web and there is a need to be able to do this in real time as the web moves past a coating head. If the finished coated web is a flame retardant material, it is desirable to be able to determine the precise thickness and density of the coating material applied to the web over its entire area. It is also highly desirable to be able to locate in a batch length of the coated web any linear extent of the coated web in which the coating material has a thickness and/or density which is outside tolerable limits. If the monitoring and control of the coating process can be effected on a continuous basis and used to locate the exact amount and density of coating material applied to a specific linear extent of the web then this would greatly assist in determining issues (such as product liability) in the event of any subsequent allegation that the coated web failed to meet a given specification, or

2 was not fit for the purpose for which it was provided.

Present coating techniques are not very reliable and are imprecise. one known method of coating a web of fabric with a thin covering of foam material comprises the use of positive displacement pumps such as, for example, monopumps which displace a given volume of foamable product to a foaming or coating head for a given area of fabric which passes the coating head in a given time. To simplify the control of the coating method, it js usual to pass a given width of fabric past the coating head, at a given linear speed, and to control the speed of operation of the positive volume displacement pumps so that the foamable product is supplied to the coating head at the desired rate.

We have found problems with this known method since, although a pump operates fairly reliably when new it becomes almost impossible to control the amount or density of the applied foam material with any accuracy when the pump begins to wear. In general, with batch processes a given volume or weight of foamable product is supplied to a hopper and pumped to the foaming or coating head, the speed of rotation of the pumps being set initially so as to be directly related to the speed of the web moving past the coating head. Consequently as soon as the pumps wear, one cannot be sqre of the exact volume and/or density of foamable product pumped to the coating head and either too much or too little foam material is coated on the web.

Another problem with the known technique is that the apparatus once set up is incapable of coping with different densities of foamable product and the varying pressure head as the foamable product is used up from the supply hopper.

A further problem has been the large amount of waste coated web which results when setting up known coating apparatus for a batch run. It has been the practice in the 1 3 past to cut very accurately sized samples of the coated web and to weigh the sample to derive a measure of the weight of coating material applied to the web. The speed of the pump is then adjusted to take account of the results of the sampling and further samples are cut and weighed. During this sampling procedure, coated web is being produced which may not have the correct amount of coating material applied to it. Many hundreds of metres of coated web may be wasted by this sampling procedure.

An aim of the present invention is to provide an ap- paratus and method for coating substrates in which there is improved control over the amount of coating material applied to the substrate.

According to one aspect of the present invention apparatus for controlling the application of a compound to a substrate is set out in the ensuing claim 1.

According to another aspect of the present invention a method of applying a coating material to a substrate is set out in the ensuing claim 5.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:- Figure 1 illustrates a fabrics and, known apparatus for coating Figure 2 illustrates apparatus constructed in accor dance with the present invention for coating webs.

Referring to Figure 1 of the drawings there is shown a prior known apparatus for coating a web of fabric material with a foam material. TIne apparatus comprises a coating head 10 to which is supplied a foamable compound. Tne foamable compound is fed from a hopper or tank 12 to the 4 head 10 by means of a volume displacement pump 14, such for example, manufactured by Monopumps Limited.

as, The web of fabric material to be coated is taken from a supply roll 16 and is pulled over'a base plate 15 past the coating head 10 which extends across the width of the web and which applies a thin coating of coating material to the web, and taken through a stenter 11 where the applied foam material is dried. The coated fabric material is then taken around rolls 18, 19 and coiled up on a motor driven take-up spool 17.

The pump 14 is geared directly to the take;.-up spool 17 (see the chain line link 13) so that it delivers foamable compound at a pre-set volumetric rate from the tank 12 to the coating head 10 for a given linear speed of the web of fabric material passing the coating head. In this way the amount of foam material applied is related to the area of the web of fabric material passing the coating head in a given time.

Unfortunately with this prior known apparatus once the pump 14 begins to wear the unique relationship between the linear speed of the web of fabric material passing the coating head 10 and the volumetric rate of foamable compound supplied to the coating head changes. As wear increases this change in the relationship becomes unacceptable. The main problem with the apparatus of Figure 1 is that it does not measure the actual volumetric rate that the foamable compound is supplied to the coating head but instead it assumes a theoretical volumetric rate displaced by the pump 14 which is only accurate when the pump is new. When the pump wears, less foamable compound (by as much as 10 per cent or even more) is pumped to the coating head and this loss is not compensated for.

Referring to Figure 2 there is shown aPparatus according to the present invention comprising a coating 1 k head 20 to which is supplied a liquid coating material, e.g. a foamable compound such as, for example, an acrylic compound. The coating head 20 typically comprises a "Foam Coater" supplied by Texicon.

The coating material is stored in a tank 22 and the amount or weight of coating material in the tank 22 is continuously monitored by a load cell 23. The coating material is supplied from the tank 22 by means of a separately controlled volume displacement pump 24 which is not geared at a fixed ratio to the speed of the web 25 of fabric material moving past the coating head 20, but which can be controlled automatically to take account of wear in the pump 24 and to take account of other factors as explained below.

The web 25 of fabric material, for example a polyester fabric, to be coated is unwound from a supply roll 26 and is passed beneath the coating head 20, which extends across the width of the web, and over a support base 40. The web, with a thin coating of coating material applied thereto, is then passed through a stenter 21 and around a series of rolls before being wound on to a motor driven take-up spool 27. The speed of rotation of. the take-up spool 27 is conveniently controlled to maintain a constant linear velocity of the web 25 past the coating head 20. The linear speed of the web 25 is monitored by a tachogenerator 28, positioned downstream of the coating head 20 on one of the shafts of the previously mentioned series of rolls, which generates a control signal 29 representative of the linear web speed which is supplied to a microproces- sor control unit 34.

The microprocessor control unit 34 also receives a control signal 30 from the load cell 23, and input signals 31 and 32 indicative, respectively, of the width of the web of fabric passing the coating head 20 and the "per cent of solids" required in the foamed coating to give a predeter- 1 6 mined dry weight "add on". As coating material is withdrawn from the tank 22 during a coating operation, the value of the control signal 30, representative of the weight of coating material in the tank, will change.

From the values of the control signals 29 and 30 and the input signals 31 and 32, the control unit 34 is able to generate a control signal 33 for controlling the speed of the pump 25 so as to apply to the web of fabric material a predetermined weight of coating material per unit area of the web to form a uniform coat4ng of coating material on the web of fabric material. Since the weight of the tank 22 is continuously being monitored, the amount of coating material pumped by the pump 25 from the tank 22 to the coating head 20 is continuously taken into account by the control unit 34. The control unit 34 also takes account of the area of the surface of the web 25 to be coated which passes the coating head 20 in a given period of time and which is a function of the web width and the linear speed of movement of the web past the coating head 20. The control signal 33 from the control unit 34 is supplied to a variable speed control 36 which controls the speed of the pump 24, and hence the density or amount of the coating material supplied to the coating head 20 is automatically controlled.

In the embodiment shown, the width of the web 25 is sensed by means of.a sensing device 41 which supplies the input signal 31 to the control unit 34. This input-signal 31 may also be used to ensure that the coating material is applied via the coating head 20 across the full width of the web 25. Although it is preferred to provide such a sensing device 41, it should be realised that information regarding the width of the web 25 could be pre-set,. e.g. in a manner similar to that for providing the input signal 32.

The control signal 30 supplied to the unit 34 provides an indication of the rate at which the coating material is Y 7 withdrawn from the tank 22 at any instant of time and the control signal 29 provides an indication of the rate at which a pre-set or sensed width of web of fabric material passes the coating head 10.

If desired, the control signals 29 and 30 and the input signals 31 and 32 can be recorded so that a record of various parameters of the coating process along the whole length of a batch of fabric material can be kept for further reference.

4 8

Claims

1. Apparatus for controlling the application of a compound to a substrate, the apparatus comprising a coating head for applying the compound to the substrate; means for effecting relative movement between the coating head and the substrate in a direction past the coating head; holding means for holding a quantity of the compound; controllable pump means operable to pump the compound from the holding means to the coating head; first means for generating, throughout the application of the compound to the substrate, a first control signal representative of the amount of compound in the holding means, second means for generating a second control signal representative of the rate of relative movement between the coating head and the sub- strate and electronic control means having first and second inputs to which said first and second control signals are respectively supplied and an output for delivering an output control signal for controlling the rate at which the pump means pumps said compound to the coating head.

2. Apparatus according to claim 1, in which the first means comprise weighing means for continuously generating said first control signal which is representative of the weight of compound in the holding means at any time.

3. Apparatus according to claim 1 or 2, wherein the measuring means comprises a tachogenerator for measuring the velocity of the substrate passing the coating head and which generates said second control signal.

4. Apparatus according to claim 1, 2 or 3, wherein the electronic control means has a third input for receiv- ing information on the width of the substrate passing the coating head.

5. Apparatus according to any one of the preceding 0 4 9 claims, wherein the coating head is a foaming head for receiving a foamable compound and means are provided for inputting to the electronic control means a reference signal indicative of the desired percentage of solids in the foamed compound applied by the foaming head.

6. A method of applying a liquid coating material to a substrate comprising the steps of pumping the coating material from a holding means to a coating head for application of the coating material to the substrate, effect- ing relative movement of the substrate past the coating head, deriving throughout the coating operation a first control signal representative of the amount of coating material contained in the holding means and a second control signal representative of the speed of relative movement of the substrate past the coating head and controlling the rate of pumping of the coating material to the coating head in dependence on the first and second control signals thereby to control the amount of coating material applied to the substrate throughout the coating operation.

7. A method according to claim 6, in which the coating material is stored as foamable material in the holding means and is applied at the coating head as foam material.

i Amendments to the claims have been filed as follows 1. Apparatus for controlling the application of a compound to a substrate, the apparatus comprising a coating head for applying the compound to the substrate; means for effecting relative movement between the coating head and the substrate in a direction past the coating head; holding means for holding a quantity of the compound; controllable pump means operable to pump the compound from the holding means to the coating head; first means for generating, throughout the application of the compound to the substrate, a first control signal representative of the amount of compound in the holding means, second means for generating a second control signal representative of the rate of relative movement between the coating head and the substrate and electronic control means having first and second inputs to which said first and second control signals are respectively supplied and an output for delivering an output control signal for controlling the rate at which the pump means pumps said compound to the coating head.

5. Apparatus according to any one of k the preceding 11 claims, wherein the coating head is a foaming head for receiving a foamable compound and means are provided for inputting to the electronic control means a reference signal indicative of the desired percentage of solids in the foamed compound applied by the foaming head.

6. A method of applying a liquid coating material to a substrate comprising the steps of pumping the coating material from a holding means to a coating head for application of the coating material to the substrate, effect- ing relative movement of the substrate past the coating head, deriving throughout the coating operation a first control signal representative of the amount of coating material contained in the holding means control signal movement of the substrate past the coating head and controlling the rate of pumping of the coating material to the coating head in dependence on the first and second control signals thereby to control the amount of coating material applied to the substrate throughout the coating operation.

and a second representative of the speed of relative 7. A method according to claim 6, in which the coating material is stored as foamable material in the holding means and is applied at the coating head as foam material.

8. Apparatus for controlling the application of a compound to a substrate substantially asherein described with reference to Figure 2 of the accompanying drawings.

9. A method of applying a foamable liquid coating material to a substrate substantially dsherein described with reference to Figure 2 of the accompanying drawings.

Published 1991 at ne Patent Office, State House. 66/71 High Holborn. IA)ndonWClR4TP. Further Copies maybe obtained from Sales Branch, Unit 6. Nine Mile Point. Cwrnfelinfach, Cross Keys, Newport NPI 7HZ. Printed by Multiplex techniques lid, St Mary Cray, Kent.