Creping process using two-position adhesive application

Mechanical creping of fibrous webs is improved by employing two creping adhesives applied at different points in the papermaking process and having relatively different adhesive properties for adhering the web to the creping surface. The process crepes the web from a conventional creping surface by applying a layer of a first creping adhesive directly onto the creping surface while applying a second creping adhesive to the web, followed by pressing the web onto the already formed layer of first creping adhesive and then creping the web from the creping surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention concerns mechanical creping of wet-laid or dry form 
(air-laid) webs. More particularly this invention concerns controlling the 
mechanical creping process by employing two creping adhesives having 
properties different then each other. 
2. Description of the Prior Art 
Paper webs are conventionally softened by working them in different ways 
such as by mechanically creping them from a surface, usually a drying 
surface such as a Yankee dryer with a creping doctor blade. Such a process 
disrupts and breaks many of the inter-fiber papermaking bonds in the paper 
web which are formed during drying. These inter-fiber bonds are the 
principle source of strength in ordinary paper since very little strength 
results from the physical entanglement of the fibers. 
Creping adhesives have been employed for adhering the webs to the creping 
surface sometimes in combination with release agents in order to control 
the degree of adhesion between the web and the creping surface. Control of 
the adhesion permits the continuous production of creped webs having 
substantially uniform characteristics imparted by the creping process. 
Creping adhesives have also been used for adhering relatively dry paper 
webs to a creping surface since such dry webs do not have the usual 
natural adherence obtained by pressing wet webs to a creping surface. 
The softness of paper webs has been increased by chemically impeding or 
preventing the inter-fiber papermaking bonds with a chemical debonder 
which also tends to weaken the sheet. Usually a wet or dry strength 
chemical is added to the sheet to make up for the strength loss caused by 
the chemical debonder. Unfortunately, the chemical debonders also tend to 
interfere with proper adhesion of the fibrous webs to a creping surface 
which tends to prevent creping of a chemically debonded web. 
Creping adhesives have been added to the paper sheet or directly on to the 
creping surface to overcome the effect of the chemical debonder and obtain 
proper adhesion between the chemically debonded fibrous sheet and the 
creping surface. 
The nature of the finished paper depends upon the mechanical forces at the 
locus of removal of the web from the cylinder, and also upon the angle of 
removal. Without a doctor blade or with a doctor blade substantially 
tangent to the circumference of the cylinder, the paper tends to have a 
smoother, "machine-glazed" finish. If the doctor blade is at an angle to 
the tangent, the finished paper is creped and this procedure is known as 
"creping off the Yankee drier." 
In spite of the many desirable advantages which accrue in creping from 
Yankee driers, there is often much difficulty in maintaining smooth 
removal of the web by the doctor blade. This operation requires a delicate 
balance between the adhesive forces holding the web uniformly on the 
cylinder surface and the releasing forces occurring at the source of 
contact with the doctor blade. The creping forces can get out of balance. 
Too great of an adhesive force can result in "pickouts" of paper, or 
fibers remaining with the dryer surface and the inability of the cleaning 
doctor to remove sufficient adhesive from the dryer to avoid buildup of 
adhesive and an irregular surface. On the other hand, too little of an 
adhesive force can result in the paper being removed from the creping 
surface without sufficient creping action being applied to the web. Many 
attempts have been made to attain this needed balance but none have been 
entirely satisfactory. The present invention provides the desired control 
and balance. 
SUMMARY OF THE INVENTION 
A method is provided for mechanically creping a web from a creping surface 
by applying a layer of a first creping adhesive directly onto the creping 
surface, applying a second creping adhesive to the web, pressing the web 
onto the already formed layer of first creping adhesive to contact the 
second creping adhesive with the first creping adhesive for adhesively 
attaching the web to the creping surface, and creping the web from the 
creping surface. The invention also provides for the first creping 
adhesive to be relatively softer than the second creping adhesive so that 
when creping the web from the creping surface with a creping doctor blade, 
the blade tends to shear the layer of first creping adhesive rather than 
the second creping adhesive. The mechanical creping action can be 
controlled by adjusting (1) the quantity of first creping adhesive applied 
to the creping surface, (2) the quantity of second creping adhesive 
applied to the web and (3) the ratio of first and second creping adhesives 
.

DETAILED DESCRIPTION OF THE INVENTION 
The drawing illustrates one type of conventional Fourdrinier papermaking 
machine with which the present invention can be used. The papermaking 
machine is illustrative of the double-felt type, on which paper furnish 10 
flows from a headbox 11 through a slice 12 onto the substantially 
horizontal surface of a Fourdrinier wire 13 through which water is 
withdrawn and upon which web formation takes place. Wire 13 is entrained 
around breast roll 14 and over a plurality of table rolls 15 to a wire 
turning roll 16. It is then fed around a lower couch roll 17 and around to 
other guide rolls 18 back to breast roll 14. One or more of the 
above-described rolls is driven and propels the Fourdrinier wire 13 
through the desired path so that the upper surface or flight moves from 
the breast roll 14 to the lower couch roll 17 and returns along the 
bottom. In addition, one or more vacuum boxes, deflectors, and hydrofoils 
(not shown) may be employed between table rolls 15 to assist in the 
removal of water from the web during its formation. 
The wet web formed on the upper surface of Fourdrinier wire 13 is 
transferred to a pickup felt 20, which is pressed into engagement with the 
web on wire 13 by means of an upper couch roll 21. The pickup felt 20 
meeting wire 13 moves in the same direction as the wire 13, as indicated 
in the drawings, and at substantially the same speed. Pickup felt 20 
carrying the newly formed web is advanced through the nip of a press 
assembly, indicated generally by reference numeral 22. Felt 20 is then 
moved around a pressure roll 23 which may be of the suction type, and 
hence, is entrained around a plurality of guide rolls 24 back to upper 
couch roll 21. A guard board 25 and shower (not shown) are employed 
adjacent the surface of felt 20 in front of the point where it contacts 
the newly formed sheet and accomplishes pickup. Guard board 25 and the 
showers clean and condition the felt to receive the wet web. 
Press assembly 22 comprises a upper press roll 26 and a lower press roll 
27, one of which is a suction press roll. A wet felt 28 is entrained over 
a plurality of guide rolls 30 and over lower press roll 27. One or more of 
the rolls contacting wet felt 28 and pickup felt 20 is driven to insure 
movement thereof at the proper speed. Moisture is removed from the newly 
formed web in the nip of a press assembly 22 and transferred into wet felt 
28. It is normally removed from wet felt 28 by a wringer roll 29. 
The formed and pressed web on felt 20 issuing from the nip of press 
assembly 22 is then pressed into engagement with the surface of the 
rotating drying cylinder 31 of a conventional Yankee dryer. The Yankee 
dryer includes a hood 32 surrounding a portion of the surface of cylinder 
31 contacted by the web. Hood 32 includes therein a plurality of air input 
nozzles 33 and an exhaust means 34 for removing air from the chamber 
enclosed by hood 32. This flow of air within hood 32 over the surface of 
the web carried on the drying cylinder 31 assists in removing moisture 
from the web and accomplishing drying. The paper web 35 shown issuing from 
the opposite side of drying cylinder 31 is removed from the surface of 
drying cylinder 31 by a conventional doctor blade 36 which accomplishes 
creping of the web. Web 35 is pulled from the vicinity of Yankee dryer 31 
by passing the web 35 through a nip formed by a pair of rolls 42, from 
which it is conventionally wound into a roll 43. 
With this description of a conventional Fourdrinier papermaking machine, 
the apparatus for applying creping adhesives in the manner of the 
invention will now be described. The creping adhesives are applied at two 
or more locations. The first location is by spray means 39 to the surface 
of the Yankee dryer 31, and the other location is by way of spray means 40 
to the wet web carried upon pickup felt 20 and/or by application of the 
adhesive into the paper furnish 10 in the head box 11 by conventional 
means (illustrated by the pipe 41). The spray means 39 which applies the 
first creping adhesive to the Yankee surface 31 consists of a series of 
spray nozzles attached to a header pipe extending across the width of the 
Yankee surface 31 in a conventional manner. The nozzles are spaced apart 
from each other so as to have overriding spray patterns. By properly 
spacing the spray nozzles in a manner known in the art, the application of 
the adhesive is generally uniform across the width of the Yankee surface 
31. 
Spray application means 40 is provided by an apparatus similar in structure 
to spray means 39, but extending across the width of the pickup felt 20 at 
a point close to where the wet paper web is pressed to the Yankee surface 
31 by press roll 23. The second creping adhesive applied through spray 
means 40 is applied to the surface of the wet paper web which will face 
the Yankee surface 31. As can be readily appreciated, the ratio of 
quantity of the first creping adhesive applied by spray means 39 to the 
quantity of second creping adhesive applied at spray means 40 can be 
accurately and quickly controlled by adjusting the flow at each spray 
means. The application of a third creping adhesive into the slurry, if 
desired, can be accomplished by well known conventional means, such as 
methods for the applicaton of wet strength resins, and is illustrated only 
schematically as pipe 41. After the paper web 35 is creped from the Yankee 
cylinder 31 by means of doctor blade 36, a residual film of creping 
adhesive remains on the Yankee surface 31. Most of this film is removed by 
conventional cleaning doctor 38, but a very thin uniform layer remains on 
the cylinder surface 31. 
Spray means 39 are positioned as close as possible after the cleaning 
doctor 38 so that the first creping adhesive applied to the Yankee surface 
31 will be heated by the Yankee surface 31 sufficiently before the wet web 
is applied to the Yankee surface to form a definitive layer of first 
creping adhesive upon which the paper web and the second creping adhesive 
are pressed. This definitive layer can be more satisfactorily formed if 
spray means 39 for spraying the first creping adhesive are positioned a 
significant distance from the location where the paper web is pressed to 
the Yankee surface 31. 
The drawing shows the first creping adhesive being sprayed from sprayer 
tube 39 onto a rotating creping surface 31 which rotates clockwise. A 
continuous layer of this first creping adhesive is formed on the creping 
surface 31 prior to the point where the web is pressed against the creping 
surface. The first creping adhesive applied to the creping surface 31 
should be applied at a rate of from about 0.01% to about 1.0% based upon 
the air-dry weight of the web. 
While the first creping adhesive is shown in the figure as being sprayed 
onto the creping surface to form a layer on the surface, other methods of 
applying the creping adhesive to the creping surface are suitable 
including the use of fountain coaters, and reverse blade coaters which are 
well known. 
With reference to the figure, the web 35 is pressed onto the creping 
surface 31 from pickup felt 20 by pressing roller 23. At this critical 
point of engagement of the web 35 onto the creping surface, the web 
already contains the second creping adhesive and a film of the first 
creping adhesive has already been formed on the creping surface 31. This 
aspect is the critical point of the invention. It is critical in 
practicing the present that: 
1. a layer of first creping adhesive is formed on the creping surface; 
2. the web is pressed onto the formed layer of first creping adhesive on 
the creping surface; 
3. at the time when the web is pressed onto the layer of first creping 
adhesive, the web has already been treated with a second creping adhesive 
so that the pressing of the web contacts the second creping adhesive with 
the already formed layer of first creping adhesive. 
The above critical sequence in the process of the present invention results 
in a web being adhesively attached to a creping surface by two discrete 
adhesives. While there may be some intermixing of adhesives at the 
adhesive interface, a layer consisting essentially of the first creping 
adhesive exists adjacent to the creping surface. 
The web 35 is adhesively attached to the creping surface 31, rotates with 
the creping surface and is creped from the creping surface by a creping 
doctor blade 36. The creping doctor blade is urged against the creping 
surface 31 with a force sufficient to overcome the adhesive force of the 
web to the creping surface and accordingly the web is creped and removed 
from the creping surface. 
A particular and unique advantage of the present invention is the 
controlability of the creping process to produce consistent uniform 
product. Because of the use of two distinct creping adhesives, the creping 
process can be controlled by adjusting the type and/or quantity of the 
first creping adhesive, and by adjusting the type and/or quantity of the 
second creping adhesive. Furthermore, the relative adhesive 
characteristics between the first and second creping adhesives can be 
adjusted in terms of there relative hardness or softness. 
The present system permits the adhesive bond with the creping surface to be 
determined primarily by the characteristics of the first creping adhesive 
while the adhesive bond with the web is determined primarily by the 
characteristics of the second creping adhesive. These bonds can be 
separately controlled. Accordingly, the web can be tenaciously adhered 
with a hard creping adhesive while the creping blade can be cutting in the 
layer of the first creping adhesive to permit good removal without 
irregular surface buildup which causes plugging. 
Problems usually associated with creping can be controlled with the present 
invention. For example a creping problem known as picking or plugging 
which results in holes in the paper and believed to be caused by excessive 
adhesion with the creping surface can be corrected by increasing the 
amount of the softer first adhesive applied to the creping surface. At 
other times the creped sheet may be too harsh with a blister type crepe 
indicating that the web is "too loose" or not adhered strongly enough to 
the creping surface. This condition can be corrected by decreasing the 
amount of first adhesive or increasing the amount of the second adhesive. 
The film of the first should be softer than the second adhesive which 
results in the blade 36 riding in the layer of first adhesive and shearing 
the layer during the creping action. In such an embodiment, there remains 
on the creping surface, 31 immediately after the creping blade 36 a layer 
consisting essentially of the first creping adhesive. Most of this layer 
of the first creping adhesive is removed by a cleaning doctor blade 38 
located behind the creping doctor blade 36 shown in the figure. A film 
having a glass transition temperature of less than about 30 10.degree. C 
will be softer than adhesives suitable for use as the second creping 
adhesive. 
In addition to individually controlling the adhesive bonds with the creping 
surface and with the web, the rheology of the film or layer of first 
adhesive can be adjusted independently of the adhesive bond imparted to 
the web by the second adhesive. Accordingly, the flow and shearing 
characteristics of the layer of first adhesive can be separately 
controlled. With such a system, the fibrous web can be tenaciously adhered 
by means of the second adhesive while the creping doctor blade can 
function in the layer or film of first creping adhesive which has film and 
shear characteristics independently selected to optimize the shearing of 
the film from the creping surface by the creping doctor blade. 
The present invention produces a more uniformly and more extensibly creped 
web in comparison to employing only the first creping adhesive because of 
the superior adhesion of the web imparted by the second creping adhesive. 
Furthermore, superior product uniformity is obtained in comparison to 
employing just the second creping adhesive because of the superior 
shearing characteristics of the layer of first creping adhesive which 
permits controlled, uniform, consistent creping which minimizes chattering 
of the creping blade and plugging of the web. 
Particularly good creping control is obtained when the first creping 
adhesive is a latex of a polymer that is essentially non-cross-linking. An 
example of such an adhesive is a non-cross-linking copolymer of vinyl 
acetate and acrylic esters. The latex is formed by emulsifying the 
copolymer that has been stabilized with a non-ionic hydrocolloid in the 
ratio of about 3 part by weight copolymer to about 1 part by weight 
hydrocolloid. The resulting latex is an emulsion of the copolymer and 
hydrocolloid having a large particular size (usually 1 micron). The 
presence of the hydrocolloid molecules in the emulsion imparts water 
redispersibility so that a dried film obtained from the emulsion is water 
redispersible when contacted with water and thereby tends to reemulsify. 
The advantage of using essentially non-cross-linking (thermoplastic) 
polymers is that the rheology of the thermoplastic polymer system in the 
emulsion is substantially retained when a dried film is formed of the 
emulsified components (non water components) even when the film is heated 
such as when the latex is sprayed onto the surface of a Yankee dryer. 
Hydrocolloids suitable for use for imparting water redispersibility to 
emulsified copolymers are well-known in the latex art and are water 
soluble polymers that function as protectors in the formulation of an 
emulsion of a non-water soluble polymer and which tend to be 
electrochemically attached to the copolymer. Typical known hydrocolloids 
are hydroxyethyl cellulose, methyl cellulose, alginates and polyvinyl 
alcohols. An example of a non-water dispersible polymer that can be 
combined with a hydrocolloid and emulsified to produce a water based 
colloidal emulsion, the solid components of which produce a dried film 
that is redispersible in water is a vinyl acetate-acrylate copolymer 
available from National Starch Corporation as Latex No. 4441 or Latex No. 
4442, which have a molecular weight of about 2,000,000, a glass transition 
temperature of about -40.degree. C and a Sward Rocker hardness of about 3. 
Water redispersible latexes, as exemplified above, should be a water based 
emulsion of a non-cross-linking polymer combined with a hydrocolloid so 
that a film of the solids in the emulsion (non-water components) is water 
redispersible, sufficiently soft to have a glass transition temperature 
lower than about -10.degree. and preferably from about -20.degree. C to 
about -50.degree. C and have a Sward Rocker hardness between about 1 and 
about 4. Such polymers usually have a molecular weight of about 2,000,000. 
Sward Rocker Hardness values and the test procedure are described in "Paint 
Testing Manual" G. G. Sward, Editor, ASTM Special Technical Publication -- 
500 and also described in "Surface Coatings And Finishes" Gordon & Dolgin, 
Chemical Publishing Co., 1954. 
There are particular advantages associated with employing the water 
redispersible latex adhesive described above as the first adhesive in 
practicing the present invention. Such latexes produce a particularly 
suitable film in which the creping doctor blade tends to ride and shear 
the film for creping the web from the creping surface and in addition any 
residue of the first creping adhesive which becomes deposited upon the 
papermaking felt or permeates other areas of the papermaking process is 
readily removable due to its water redispersibility. However, other 
adhesives are suitable for use as the first adhesive in practicing the 
invention provided they are softer than the second adhesive as can be 
indicated by a lower glass transition temperature for a film of the first 
adhesive than a film of the second adhesive. Relative softness between the 
two adhesives can also be determined by measuring the adhesive strength of 
each adhesive with the weaker adhesive being softer. Another good 
indication of relative softness is the modulus of elasticity. A lower 
modulus indicates a softer adhesive. 
Latexes made from polymers capable of forming an emulsion in water either 
with or without normal emulsifiers are suitable. Preferably a film of the 
polymer solids has an initial modulus of less than about 2 .times. 
10.sup.7 dynes/cm.sup.2 and a glass transition temperature less than about 
+10.degree. C. The initial molulus referred to above is an initial modulus 
at 1% elongation for a film of a solid being tested according to ASTM Test 
D 638. Examples of suitable emulsion polymers (latexes) are water 
emulsions of acrylates; styrenebutadienes; polybutadienes; acrylonitriles; 
acrylontrile-butadienes; polyurethanes; ethylenevinyl acetates; polyvinyl 
alkyl ethers; polyacetals; polyterpenes; vinyl acrylics; ethylene-vinyl 
acrylates; polychloroprenes; polyhalohydrins; acrylate-acetate copolymers; 
plasticized polyvinyl chlorides and plasticized polyvinyl acetates. An 
example of a commercially available latex suitable for use as the first 
adhesive though it does not produce a water redispersible film is an 
acrylic ester copolymer emulsion available from Rohm & Haas under the 
tradename HA-8, having a glass transition temperature of about -13.degree. 
C and an initial modulus of about 7 .times. 10.sup.6 dynes/cm.sup.2. 
Adhesives suitable for use as the second adhesive include the adhesives 
normally used as creping adhesives either added to the wet end of the 
papermaking process or to the web prior to contacting the creping surface. 
Such adhesives include the polyamines, polyamides, water soluble 
acrylates, animal glues, polyacrylamides, and polyacrylic-polyacrylamide 
copolymers. The above adhesives are water soluble have a viscosity in the 
range of about 50 cps to about 1,000 cps for solution having a solids 
content from about 7% to about 70% by weight; and a molecular weight of 
from about 150,000 to about 1,000,000. 
The second adhesive when added to the wet end is added in amounts to result 
in from about 0.1% to about 4.0% adhesive based upon the air dry weight of 
cellulosic fibers in the furnish. When added directly to the formed web, 
the second adhesive should be added in amounts of from about 0.05% to 
about 4.0% based upon the air dry weight of the web. 
The method of the present invention may be applied to a wide variety of 
webs in order to form creped sheet materials by the easily controllable 
process of the present invention. This means that a wide variety of 
processes may be utilized to form the web. The preferred means is by 
depositing fibers on a foraminous surface from a suspension in a fluid 
medium such as a water based furnish deposited upon a Fourdrinier wire as 
illustrated in the drawing. The invention is particularly suitable for 
creping wetlaid sheets whose natural fiber to fiber bonding in the formed 
web has been impeded or prevented either by chemical means (chemical 
debonders) or by the avoidance of wet pressing during the sheet formation 
and drying. 
Suitable webs are preferably those having a basis weight between about 5 
and about 55 pounds per 2,880 square feet. Such basis weight sheets 
particularly when chemically debonded derive the most benefit from the 
improved and controllable creping process of the present invention.