US3676184A - Method for controlling varying liquid penetration of a continuous paper web - Google Patents

Abstract

A METHOD FOR CONTROLLING COATING LIQUID PENETRATION INTO THE SUBSTRATE OF A CONTINOUS WEB WHICH INCLUDES APPLICATION OF A BARRIER LIQUID TO THE FIRST SIDE OF THE WEB PRIOR TO THE TIME THE COATING LIQUID IS APPLIED TO THE SECOND SIDE OF THE WEB.

Description

fl M M w 1 j TMi W i a. W w M M W n M .r/ M. MM 4 v N w%% 5% W A I W. E. SPEARIN METHOD FOR CONTROLLING VARYING OF A CONTINUOUS P Filed Aug 22 July 11, 1972 United States Patent Office 3,676,184 Patented July 11, 1972 3,676,184 METHOD FOR CONTROLLING VARYING LIQUID PENETRATION OF A CONTINUOUS PAPER WEB Walter E. Spearin and Harold S. Vanderhei, Roaring Spring, Pa., assignors to Combined Paper Mills, Inc.,

Combined Locks, Wis.

Filed Aug. 22, 1969, Ser. No. 852,426 Int. Cl. B05c 9/04 US. Cl. 117-68 4 Claims ABSTRACT OF THE DISCLOSURE A method for controlling coating liquid penetration into the substrate of a continuous web which includes application of a barrier liquid to the first side of the web prior to the time the coating liquid is applied to the second side of the web.

This invention relates to the coating of paper during its manufacture, and specifically to a method for controlling penetration of a liquid or liquids into the substrate of a continuous web, such as a coating liquid applied at a coating station.

Sliding roll coaters are known which include a pair of substantially uniform diameter rolls in a coating station. The rolls, when brought into peripheral contact with one another, form a nip area through which a continuous web of paper to be coated is passed. In a conventional coating station, a positioning roll or other equivalent device may be located upstream from the nip area so as to ensure movement of the moving web vertically downwardly into and through the nip area, the moving web being coated on one or both sides as it moves through the nip area. The positioning roll upstream from the nip area may however be so positioned as to cause the moving web of paper to be lapped against one of the rolls in the coating station, usually the hard surfaced supporting roll, so that only a single pool of coating or other liquid medium is formed, and only one side of the web is coated. In this instance it may be desirable to apply a barrier coat to the surface of the web opposite to the surface to which the coating liquid is applied to prevent strike through of the coating. Various expedients may be employed, one of which involves the formation of a pool of barrier liquid in a nip area formed between a barrier liquid roll which is in peripheral contact with the supporting roll. A thin film of barrier liquid is picked up from the pool by the supporting roll and carried around and applied to the opposite surface of the web as it passes through the coating station nip area at the time the web makes contact with the pool of coating liquid.

Further modifications of the above described system may be employed to advantage, such as the maintenance of a speed differential between the supporting roll and the coating roll in the coating station and the use of a softer surface on the sliding coater roll, and it will be understood that these expedients may be employed concurrently with the employment of the instant invention.

The liquid applied to the web at the coater station, which for convenience will hereinafter be referred to as the coating liquid, may have penetrating qualities with regard to the substrate of the web which may be detrimental to the quality of the final product. The coating liquid may for example contain encapsulated dye materials which should not be permitted to strike through the paper and reach the opposite side because of the possibility of premature rupture of the encapsulated materials and the resultant degradation of the quality of the surface of the paper.

Applying a barrier liquid to the opposite side of the web tends to counteract this penetrating or strike through characteristic of the coating medium. However, when the application of the barrier liquid to the opposite side of the web commences at substantially the same instant the coating material is applied to the web, strike through of the coating material may not be acceptably controlled. The penetrating ability of the coating material is governed by several factors which may vary from coating to coating, such as the nature of the liquid (i.e. the viscosity, temperature, and polarity), the thickness of the film, and the contact time between the liquid and the continuous web. If these factors combine to cause quick strike through, a poor quality paper may result.

Accordingly a primary object of this invention is to provide a method and apparatus for controlling penetration of a liquid or liquids into the substrate of a continuous web, particularly a liquid or liquids applied at a coating station at a paper making machine.

Another object is to provide a method and apparatus as above described which is simple in construction and operation and may be quickly placed into and out of operating position during normal down time of a paper making machine, whereby no additional down time, and expense, due to set up of the system is incurred.

Yet another object is to provide an apparatus which will accomplish the foregoing objects and which can be fabricated by a relatively slight, and inexpensive, change in the basic equipment currently used in many paper mills.

Other objects and advantages of the invention will be apparent from the following description of the invention.

The invention is illustrated more or less diagrammatically in the accompanying figures, wherein:

FIG. 1 is a schematic view of a portion of a paper making machine which includes the present invention, and

FIG. 2 is an end view, partly diagrammatic in nature, to an enlarged scale of an exemplary apparatus for practicing the invention.

Like reference numerals will be used to refer to like parts throughout the following description of the figures.

Referring first to FIG. 1, a web having a substantial moisture content is indicated generally at 60 passing through a dryer section 61 in a paper making machine. After leaving the drying section 61 the Web 60 enters a breaker stack, indicated generally at 62, after which it enters a coating station which might be a size press indicated generally at 63. After leaving the size press 63 the web 60 enters additional drying means, indicated at 64, after which it enters a first calendar stack 65, then a second calendar stack 66, and finally into reel section 67.

Referring now to FIG. 2, the size press section 63 includes a supporting roll 68 and a coating or applicator roll 69. The supporting roll may be a hard surfaced roll such as, for example, a steel Walled cylindrical shell covered by a thick 304 stainless steel cover 70, the entire assembly being approximately 26" in diameter. Preferably the surface is ground to a fine finish with a flat profile. The applicator roll 69 is of the same diameter and may for example be constructed of a steel walled cylindrical shell 3 covered with about a 1" thick rubber cover which may for example be equivalent to Stowe-Woodward Micromate S brand with a rubber hardness of nominal 35 P and J Plastometer (92 Shore A Durometer). The rubber cover 71 is prepared by grinding to a fine final finish with a slight crown.

The nip 72 formed by the peripheral contact of these two rolls is controlled in width by the amount of force exerted along the horizontal plane 73 passing through the axes of the rolls by a lever system actuated by any suitable mechanism, such as a piston-cylinder arrangement indicated diagrammatically at 59. As a specific example, a nip pressure of approximately 80 lbs. per linear inch may be used. The piston-cylinder arrangement 59 functions to move applicator roll 69 from the solid line coating position to the dotted line disengaged position. A pool of liquid, which may for purposes of description be considered to be a coating liquid, is indicated at 74. Any suitable means may be employed for replenishing the pool as the coating is applied to surface 75 of the moving web 60.

Means are indicated at 77 for applying a liquid medium to the side 76 of the web in contact with supporting roll 68 so as to provide a sealing or barrier action and/or curl control at the same time that the coating liquid 74 is applied to the opposite sides 75 of the web. The application of a film of sealing or curl-control liquid, 78, which will hereafter be referred to as a barrier liquid, is accomplished by forming a pool 79 of the barrier liquid in the nip between rolls 77 and 68. The barrier liquid may be supplied from any suitable means such as the header 80 which is indicated schematically. The barrier liquid cylinder 77 is moved into and out of nip forming engagement with roll 68 by an air piston-cylinder arrangement indicated generally at 81. Roll 77 may for example be a slightly crowned steel-wall cylindrical shell covered with approximately a 1" thick layer of neoprene self-skinning rubber with a P and J Plastometer reading of 80 (Shore A Durometer reading of 63). In operation, a typical nip loading may be on the order of about 23 lbs. per linear inch.

A web positioning roll is indicated generally at 84. In its illustrated position roll 84 causes web 60 to make contact with roll 68 along a lapped area subtended by an are indicated at c. It will be noted that the coating liquid in nip 72 contacts web 60 in that portion of the total lapped area represented by the arc subtended by angle a, and that web 60 contacts roll 68, but not the coating liquid 74, in that portion of the total lapped area represented by the arc subtended by angle b.

Roll 84 may however be positioned at any desired location by adjusting means 85, indicated diagrammatically as a piston-cylinder arrangement. If for example the equipment is required to operate as a conventional coater roll 77 may be moved to the disengaged position, and adjusting mechanism 85 actuated to move roll 84 to a position in which web 60 passes vertically downwardly to the nip area 72, the web then receiving a coating on both sides.

A guide roll is indicated at 86, and a spreader roll at 87. Roll 87 may be a steel Walled cylindrical shell covered with a thin Teflon film to provide easy release and self cleaning properties as the wet web passes over its surface. In addition the roll 87 may be grooved along its surface in spiral fashion emanating from the center line in each direction to provide a spreading action as the web passes over the surface. The imparting of a spreading action tends to remove any wrinkles in the web caused by expansion of the web due to Wetting action resulting from application of liquids by coating roll 69 and liquid barrier roll 77.

The use and operation of the invention is as follows.

The nature and intensity of the liquid coat applied in nip area 72 will be determined by several factors, in-

4 cluding the nature of the liquid (viscosity, temperature, and polarity). If the nature of the coating liquid is such that strike-through to surface 76 is a problem a liquid barrier is applied from the surface of roll 68, the liquid barrier being a film drawn from the replenishable pool 79 of a barrier fluid.

If the coating material 74 has quick strike through characteristics the placement of the liquid barrier coating on web surface 76 may not be effective if web 60 comes in contact With roll 68, at the same instant the web contacts coating pool 74. That is, if Web 60 makes contact with roll 68 along an area defined by the arc subtended by angle a, the liquid barrier may not be completely effective to prevent penetration into the substrate of the web 60.

To ensure formation of a liquid barrier which will prevent penetration of coating material 74 into the substrate of the web 60, positioning roll 84 is placed in the illustrated position so as to cause web 60 to be lapped against the surface of roll 68 along the additional distance indicated by the arc substended by angle b. Thus, as any point on the web moves along are I) it is absorbing barrier liquid from the surface of roll 68, and by the time any given point reaches that point at which contact with coating liquid 74 commences, the barrier liquid will be formed and partially dispersed on the surface 76 of the web. The barrier liquid will of course continue to strike in as the web moves from the initial contact point with liquid 74 down to the apex of the nip area at which time contact is broken with roll 68. The effect of the barrier coat is to fill the pores of the web starting from the surface 76, and thereby prevent undesirable strike through of the coating liquid 74 starting at a later time from surface 75.

The magnitude of angle b is definite, but variable, as determined by placement of roll 84 with respect to roll 68. By controlling the lap area of the web against roll 68 the contact time between the liquid and the continuous web may be controlled, and the control of this contact time represents the primary means for controlling penetration of the liquid derived from pool 74.

It will be understood that various modifications may be made within the spirit and scope of the invention by those skilled in the art. Accordingly it is intended that the foregoing description be taken as illustrative only, and not definitive, the scope of the invention being defined by the scope of the hereinafter appended claims when interpreted in the light of the foregoing specification and the pertinent prior art.

What is claimed is:

1. In a single station paper coating method the steps of applying a film of penetration controlling barrier liquid to a first roll in a two roll coating station, initiating transfer of said film of penetration controlling barrier liquid to one side of a moving web of paper by contacting said film bearing first roll with said one side of said moving Web of paper while the other side of said moving web of paper is uncoated, and

thereafter, and prior to drying of said barrier liquid, contacting said other side of said moving web with a liquid coating material having substantially instant strike through capability,

initial contact of said barrier liquid with said web occurring at the coating station at a point in time sufficiently prior to contact of said coating liquid with said web such as to enable penetration of the sub strate of the moving web by the barrier liquid and thereby preclude any substantial strike through of thebcoating liquid to said one side of the moving we 2. The method of claim 1 further characterized in that the barrier liquid is applied in the same coating unit in which the coating liquid is applied.

3. The method of claim 2 further characterized in that the barrier liquid is applied by one of the rolls forming the nip area at which the coating liquid is applied.

5 4. The method of claim 3 further including the step of lapping the web against the roll which applies the barrier liquid to the web, the initial point of contact of the web with said r011 being upstream from the point at which said web initially contacts the coating liquid.

References Cited UNITED STATES PATENTS 668,301 2/1901 Wells et al 1171 l1 UX 1,195,888 8/1916 Wheelwright 117--68 UX 1,402,288 1/ 1922 Fisher 117-68 2,229,316 1/1941 Van Clecf 11768.5

Muggleton 117--68 X Bright 117--68.5 X Muggleton 117-68 X Hruby et al. 117-68 X Streb et a1. 117-111 X Korpman 117-155 X Bergstein 11760 WILLIAM D. MARTIN, Primary Examiner 10 B. D. PIANALTO, Assistant Examiner U.S. Cl. X.R.

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