US2936733A

US2936733A - Apparatus for coating

Info

Publication number: US2936733A
Application number: US721503A
Authority: US
Inventors: Duggins Ray Brown
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1958-03-14
Filing date: 1958-03-14
Publication date: 1960-05-17
Anticipated expiration: 1977-05-17

Description

May 17, 1960 R. B. DUGGINS APPARATUS FOR COATING Filed March 14, 1958 INVENTOR RAY BROWN DUGGINS QM 7Z% ATTORNEY This invention relates to coating non-fibrous, organic sheet materials and more particularly, to an apparatus for coating films, webs and-sheets of regenerated cellulose. Regenerated cellulose sheet material, as it comes from the casting machine, possesses properties which limit its utility essentially to ornamental and sanitary protective applications. However, the prior art is replete with coating compositions which serve to make'the film commercially more attractive. There arecoatings to control the moisture andgas permeabilities of the film, to increase its chemical resistance, to improve its heat-sealability, to add durability to the film and to improve surface slip and crease resistance of the film.

The coatings are usually applied from solutions or aqueous dispersions by passing the regenerated cellulose film through a vessel, the dip tank, containing the solution or dispersion. Thereafter, the coated film is passed through a doctoring or smoothing device which regulates the amount of the coating composition left onthe film. The film is then dried, usually byheating to evaporate the volatile solvent or the aqueous dispersant. ,p I

More specifically, the film in the form of a continuous web' is led over a guide roll' into an ordinary tank in which a rod or roll or other guide means is located. The guide roll is submerged in the liquid inthe tank and thefilm web is led around it. The web emerges from the 'tank:in a substantially vertical'direction and; is then led to locations where it is heated and dried. Prior to leaving the dipping location, the web is passed through the nip of doctor rolls to remove excess coating liquid. These rolls may be located below, at, orabove the surthe face of the liquid in the tank. To prevent premature gelation of the coating, it is preferred to partially" submerge the doctor rolls-in the tank.

'The above-described'dlp-coatmg proeess has operated successfully for many years (refer to U.S. Patent No. 1,826,697, issued October 6, 1931). However, with the advent of high speed casting, i.e., 1'00 yards/minute and above, with the accompanying necessity for coating at 7 high speeed, important problems have arisen. The appearance of coating smears on the surface of the-film with the necessity for discarding such footage has'made the increase in production almost futile. The smears are at their worst when the doctor rolls, to prevent premature gelation of the coating, are disposed at least partially below the surface of the liquid. The use of an aqueous dispersion rather than a solution as the coating composition, while being economical in the use of water rather than an organic solvent, further intensifies the smear problem.

An object of the invention, therefore, is to provide an apparatus to reduce coating smears substantially. Other objects will appear hereinafter.

The objects are accomplished by an apparatus comprising a vessel adapted to contain a coating composition liquid; guide means located in said vessel below the level 2,936,733 Patented- May 17, 19 0 of the liquid therein adapted to submerge the travelling web of film and to change its direction of travel from downwardly to substantially vertically upward; means located above the guide means and at least partially below theliquid level in said vessel adaptedto regulate the amount of coating liquid on the surface of the emerging travelling'film; means disposed within'the pocket formed by the film web travelling downwardly and then substan tially upward adapted to feed coating liquid continuously into said vessel; and meansfor removing excess coating liquid from the vessel disposed at the upper periphery of said vessel. Q

Figure 1 is a plan view ofrone embodiment of-the' apparatus of the present invention;

Figure 2 is a'sectional view along line 22 of Figure 1; and

Figure 3 is a plan view of another embodiment of the apparatus of the present invention.

Referring to the drawing, uncoated regenerated cellulose film- 10, the so-called base film, is unwound from roll 11 and is guided over roll 12 into the dip tank'13 which contains a bath of the coating composition. Sub merged in the coating bath 14 of Figure 1 is a guide or dip rod 15,. around which" the film web is led in'th'e tank; The coated film as itemerges from the coating bath 14 passes through the nip of the juxtaposed doctor rolls" 16 and 17 whereby excess'coating solution is removed from the surface of the film. The doctor rolls are mounted on

rotatable shafts

18 and 19, each of which extends at one end through the walls of the tank to be rotated by means not shown, and which at the other end is journaled in a suitable hearing. The shafts are adjustable in the horizontal'plane for regulating the nip between thedoctor rolls and providing the desired coating thickness. The film 10, after passing between the doctor rolls,

is led into a dryer not shown wherein the solvent or the dispersant for the coating composition is evaporated.

* The coating composition, either as a dispersion or in a solution, is led into the tank through a slotted distributor tube 20 critically located in the envelope formed by the film and the doctor roll 16. Alternatively, as shown in Figure 3, the dip rod may be'hollow' and suitably slotted to be a combination dip rod-distributor tube 21; However, the use of a distributor tube separate from the dip rod as in Figure 1 permits removal and cleaning of the distributor tube without disturbing the" dip rod. It is also desirable that the slot 22 in Figure- 1 or 23in Figure 3 be located so that coating liquid feeds upwardly, substantially against roll 16. The coating liquid thus flows upwardly andthe excess flows over the outer rim or p'eriphery of the vessel 13. ..--Additional inlets" for bath in the base or walls of the tank, although not necessary to the present invention, may be used at start-up or to supply supplementary bath.

It is critical to the present invention that the coating composition liquid be forced to overflow at a point or points on the rim of the dip tank 13 remote from the place of emergence of the coated film from the tank. The means used to receive the overflow liquid is not important. In Figure 1 an appropriately sloped trough 24 surrounds the vessel 13. Overflow liquid is led through the trough and pipe 26 to the supply tank, not shown, located at a lower level wherein the coating composition is replenished and pumped into the dip tank 13 through the distributor rod as described previously. In Figure 3 a vessel 25 having an opening in its base completely encases the vessel 13 to receive overflow liquid and to pass the liquid to the supply tank.

It is believed that the success of the present invention may be attributed to the critical locations of the entrance and exit of coating composition liquid to and from 3 the dip tank, i.e the critical, location of the distributor tr be in the previously mentioned pocket or envelope and the use ofthe overflow as a means of circulating the coating composition liquid. At the high coating speeds required in the present competitive market, much foam. is created by air whipped into the coating composition liquid by the rapidly moving film and by the agitation of the liquid by the rotating doctor rolls. It is believed that this foam which accumulates on the surface. of the liquid in the dip tank passes into the nip of the doctor rolls and is squeezed into various areas on the surface of the film. It is these areas which may become visible after drying as coating smears. By the use ofthe present invention, any foam formed on the surface of the coating composition liquid will be caused, to flow over the sides of the dip tank away from the travelling The apparatus is particularly advantageous for high speed" coating regenerated cellulose film with aqueous dispersions of vinylidene chloride polymers as described in, US. Patent No. 2,684,919,. In actual tests wherein regenerated cellulose film was coated with vinylidene chloride polymers, a 35% reduction in the amount of rejected for coating smears was noted when coating at speeds of 100-150 yards/minute; a. 100% reduction was. noted at speeds above 150 yards/minute over the prior art method wherein coating liquid was brought into the tank solely from-outside the aforementioned pocket and excess liquid left through an outlet in the bottom of the tank.

Besides coating regenerated cellulose film, the invention; is applicable to coating other non-fibrous organic sheet materials such as polyester films, cellulose ester films, polyamide films, polyethylene films, etc. with a variety of film-forming coatings from aqueous dispersions or organic solvent solutions. More specifically, the aqueous dispersions described in US. Patent Nos. 2,278,415,; 2,570,478; and 2,684,919 and the solvent solutions described in U.S Patent Nos. 1,826,696; 1,997,583; 2,079,395; 2,205,210; 2,147,180; 2,236,546; 2,462,185; 2,686,744; and 2,726,171 may be used to coat regenerated cellulose, cellulose acetate, ethyl cellulose, cellulose nitrate, vinylidene chloride polymers, nylon, polyethylene and polyethylene terephthalate films using the apparatus :13; the present invention. The sheet materials coated in the apparatus of the present invention are suitable for use as packaging materials for food stufis, textiles, hard.- ware, etc., as tank linings, bottle cap seals, etc.

Since many widely different embodiments of the apparatus can be designed without departing fromthe spirit and scope of this invention, it is, understood that the invention is not limited except as defined; by the appended claims.

What is claimed is:

15. Apparatus for coating a travelling-web ofzfilrn com,-

tion liquid; means disposed in said vessel below the level of liquid therein adapted to guide a travelling web of film therearound; means disposed above said guide means adapted to regulate the amount 'of'coating composition liquid on the surface of the emerging web of film; means disposed solely within the pocket formed by the web travelling around said guide means to feed coating composition liquid continuously; and means disposed at the periphery of said vessel for removing excess coating compositionliquid from. said vessel.

2; An apparatus as in claim 1. wherein the guide means disposed in said vessel is hollow, slotted and adapted also to serve as the means for feedingcoating composition liquid continuously.

3. An apparatus as in claim 1 wherein said means adapted to regulate the amount of coating composition liquid on the surface of the emerging web of film is composed of two rotatable rolls spaced from each other in juxtaposition to provide a nip, theweb offilm passing through the nip therebetween.

4. An apparatus as in claim 3 wherein said rolls. are at least partially submerged in the coating composition liquid in the vessel. I

5. Apparatus for continuously'coatingatravelling web of film comprising a vessel adapted to contain a coating composition liquid; guide means disposed in said vessel below the level of'liquid therein adapted to submerge a travelling web of film and to change the direction of travel of said film from downward to substantially vertically upward; two rotatable rolls in juxtaposition to provide a nip therebetween disposed above the guide means and at least partially below the level of liquid in the vessel-adapted to receive the emerging web of film therebetween and to regulate the amount of coating composition liquid on the surface of the emerging web of film; an inlet for coating composition liquid disposed solely within the envelope formed by the web of film travelling around said guide means adapted to. feed coating composition liquid'substantially upwardly and sub.- stantially toward one of said rotatable rolls; and means disposed around the rim of said'vessel remote from the emerging web of film adaptedto receive overflowing coating coposition liquid.

6'. An apparatus as in claim 5 wherein said guide means is hollow, slotted and adapted to serve also asthe inlet for coating composition liquid.

Koch Mar. 30, 19.26 2,357,536 .Sept., 5, 1944. 2,542,064 Feb. 20, 1951