Method for preparing starch based corrugating adhesives using waste wash water

A starch based adhesive for use in manufacturing corrugated paper and board is prepared in a single preparation tank 20 by admixing, under high shear vortex mixing, a first portion of aqueous medium, a first starch portion, an aqueous sodium hydroxide, a borating additive, a second portion of aqueous medium and a second starch portion to produce a finished starch adhesive. At least one of the first and second portions of aqueous medium comprises a mixture of fresh water and recycled wash water selected from the group consisting essentially of untreated flexographic printing press wash water, untreated corrugator wash water, and mixtures thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to the preparation of starch based 
corrugating adhesives and, more particularly, to the preparation of starch 
based corrugating adhesives using as the aqueous medium for the adhesive a 
mixture of fresh water and recycled unfiltered wash water from the 
corrugator press and/or the flexographic printing press wash processes. 
In the corrugated paperboard industry, corrugator presses are used to glue 
together sheets of paper with starch based adhesives to form paperboard 
products. Flexographic printing presses are extensively used to print 
various information on the paperboard products. Both these corrugator 
presses and these flexographic printing presses must be periodically 
cleaned by flushing with large quantities of water. The waste wash water 
from the cleaning of the corrugator presses contains unused starch 
adhesive, machine oils and paper lint. Similarly, the waste wash water 
from the cleaning of the flexographic printing presses contains 
contaminants such as ink solids, detergents, machine oils and paper lint. 
Ideally, the waste wash water from the corrugator presses and the 
flexographic printing presses should be recycled for use elsewhere in the 
plant rather than merely being discarded. A preferred use for this waste 
wash water would be as part of the aqueous medium used in preparing the 
starch adhesives for the corrugating process. Unfortunately, the presence 
of contaminants, particularly ink solids and ammonium ions in the 
flexographic printing press waste wash water, have prevented use of this 
waste wash water in the preparation of the starch based adhesives without 
prior treatment to remove these contaminants. 
The conventional two-phase process for preparing corrugating adhesives, as 
well as various modifications thereof, is described in detail in a 1977 
TAPPI monograph entitled "Preparation of Corrugating Adhesives". In the 
typical two-phase process described therein, the starch based adhesive is 
prepared in two separate portions, i.e., a cooked starch portion referred 
to as the "carrier starch" and an uncooked portion referred to as the "raw 
starch". 
Typically, the carrier starch is prepared in a first tank by adding a first 
amount of fresh water along with a desired amount of a first starch, 
typically a corn starch either in raw or modified form, and the mixture 
agitated to form a starch slurry. Caustic soda, normally as a 50% sodium 
hydroxide solution, is then admixed into this starch slurry to chemically 
cook the starch thereby producing the carrier starch portion. 
In a second tank, the raw starch portion is prepared by adding a second 
amount of fresh water along with a desired amount of a second starch, 
typically an unmodified, i.e., raw, corn starch, and agitated to form a 
raw starch slurry to which a borating compound, typically in the form of 
boric acid or borax, is also added. After the raw starch portion has been 
thoroughly mixed, the prepared cooked starch portion is added thereto and 
thoroughly mixed therewith to yield the product starch adhesive typically 
having a starch solids content of about 17 to about 25 percent by weight 
and a viscosity in the range of about 150 to about 250 centipoises. 
This finished starch adhesive is passed to a relatively small, typically 
100-150 gallons capacity, storage tank from where it is circulated to the 
corrugator on demand. Because the finished starch adhesive is quite 
susceptible to thickening or thinning and viscosity breakdown, the supply 
of finished starch adhesive is deliberately held at low levels and fresh 
starch adhesive is almost constantly being generated and used before it 
breaks down. Further, it is customary to keep the finished starch adhesive 
in circulation and to maintain the finished starch adhesive at a constant 
temperature of about 100.degree. F. to about 105.degree. F. (about 
37.5.degree. C. to 40.5.degree. C.) to forestall thickening or thinning. 
As noted previously, conventional practice is to use fresh water only as 
the aqueous medium in preparing starch adhesives even though the 
desirability of disposing of waste wash water by using it in the starch 
adhesive preparation has long been recognized. One proposal for using 
flexographic printing press waste wash water is presented in U.S. Pat. No. 
3,970,467. As disclosed therein waste wash water from the flexographic 
press is treated to remove ink solids and ammonium ions from the 
flexographic press waste wash water and then pass the ammonium ion free 
water to the starch adhesive preparation tanks. It is stated in U.S. Pat. 
No. 3,970,467, that when untreated flexographic press waste wash water was 
used as a replacement for fresh water in preparing the cooked (primary or 
carrier) starch portion of the adhesive formulation, aggregates of 
coalesced starch were formed which resulted in an unworkable adhesive. It 
is further stated in U.S. Pat. No. 3,970,467, that even when untreated 
flexographic press waste wash water was used as a replacement for fresh 
water only in preparing the uncooked (secondary) starch portion, the 
resultant adhesive formulation exhibited unacceptably higher viscosities 
and gel points than adhesive formulations produced with fresh water or 
treated flexographic press waste wash water. Unfortunately, the additional 
process step necessary to appropriately treat the flexographic press waste 
wash water add further complication and cost to the adhesive preparation 
process. 
SUMMARY OF INVENTION 
It is an object of the present invention to provide a method for preparing 
starch based corrugating adhesive wherein waste wash water is used as part 
of the aqueous medium for preparing the adhesives. 
In the method of the present invention, a starch based adhesive suitable 
for use in manufacturing corrugated paper and board is prepared by 
admixing a first portion of aqueous medium, a first starch portion, an 
aqueous sodium hydroxide solution, a borating additive, a second portion 
of aqueous medium and a second starch portion to produce a finished starch 
adhesive. Advantageously, in the method of the present invention, at least 
one of the first and second portions of aqueous medium comprises a mixture 
of fresh water and recycled wash water selected from the group consisting 
essentially of untreated flexographic printing press wash water, untreated 
corrugator wash water, and mixtures thereof. 
Most advantageously, the starch based adhesive is prepared via the method 
of the present invention in a single preparation tank equipped with a high 
shear vortex mixer in the following manner. To initiate the process, a 
first portion of the aqueous medium is introduced into the tank and then a 
first portion of starch is introduced into the tank. Next, an aqueous 
solution of sodium hydroxide is metered into the tank and the mixer 
activated to thoroughly admix the starch and sodium hydroxide and 
chemically cook the starch thereby producing a cooked starch liquor. A 
borating additive, preferably borax or boric acid, is next added to the 
cooked starch liquor to stable viscosity. A second portion of aqueous 
medium is then added to the cooked starch liquor to dilute its solids 
content prior to adding a second portion of starch to the diluted cooked 
starch liquor. After sufficient mixing under the action of the high shear 
vortex mixer, the liquor is drained from the preparation tank to a 
collection tank as the finished starch adhesive product ready for use on 
the corrugator.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawing, there is schematically depicted therein a 
system for preparing starch based adhesives suitable for use in producing 
corrugated paper products. In the process of the present invention, a 
first portion of an aqueous medium, a first starch portion, an aqueous 
sodium hydroxide solution, a borating additive, a second portion of an 
aqueous and a second starch portion are admixed in a single preparation 
tank 10 to produce a finished starch adhesive which is transferred through 
line 12 via pump 14 to a companion holding tank 20 for brief storage, 
typically for no more than 30-45 minutes, therein. The finished starch 
adhesive is pumped on demand from holding tank 20 via pump 24 to a 
corrugator press 35 so as to provide a continuous supply of adhesive for 
combining paper elements to form the corrugated product. 
In a typical system for carrying out the present invention, the preparation 
tank 10 has a 150 gallon capacity and its companion holding tank 20 has a 
200 gallon capacity. To facilitate accurate weighing of the ingredients 
comprising the adhesive formulation, the preparation tank 10 is 
advantageously suspended on electronic load cells (not shown). 
Additionally, the preparation tank 10 is equipped with a high shear vortex 
mixing means 30 for efficiently admixing the various ingredients 
comprising the adhesive formulation. The storage tank 20, if desired, may 
also be equipped with a mixing means 32 for maintaining the finished 
starch adhesive in circulation during storage. 
In the preferred embodiment of the method of the present invention, the 
cooked portion of adhesive is formed first in the preparation tank 10 by 
slurrying a first portion of starch in a first portion of the aqueous 
medium and then admixing therewith an aqueous solution of sodium hydroxide 
under the high shear vortex mixing action generated by the mixing means 
30. Borating additive, most advantageously borax or boric acid in a dry 
powder form, is admixed with the cooked carrier starch to stabilize the 
viscosity of the cooked carrier starch at its lowest or base viscosity 
which corresponds to a thorough dispersion of the starch and complete 
disruption of the starch granules. At this point, a second portion of 
aqueous medium is introduced into the preparation tank 10 and admixed with 
the cooked carrier starch under the high shear vortex mixing action 
generated by the mixing means 30. This additional aqueous medium serves to 
dilute the cooked carrier starch and bring its viscosity down to a low 
level prior to adding a second portion of starch, typically raw, that is 
unmodified starch, to the cooked carrier starch as the final ingredient of 
the adhesive formulation. After sufficient mixing, the finished adhesive 
formulation is transferred to the holding tank 20. 
Unlike prior art processes, the process of the present invention makes use 
of waste wash water from the wash-up of the corrugator press and/or the 
flexographic printing press as a portion of the aqueous medium used in 
preparing the starch adhesive. In the process of the present invention, at 
least one of, but most advantageously both, the first portion of the 
aqueous medium, which is used to initially slurry the uncooked carrier 
starch, and the second portion of the aqueous medium, which is used to 
subsequently dilute the cooked starch liquor prior to the addition of 
additional raw starch, comprise a mixture of fresh water and recycled wash 
water selected from the group consisting essentially of untreated 
flexographic printing press wash water, untreated corrugator wash water, 
and mixtures thereof. Most advantageously, this mixture comprises about 
equal parts of fresh water and recycled wash water, with the recycled wash 
water most advantageously comprising a mixture of about equal parts of 
untreated flexographic printing press wash water and untreated corrugator 
wash water. 
It is to be understood that the term "untreated" as used herein with 
respect to waste wash water means that the wash water has not been 
subjected to any type of flocculation, filtering or other treatment to 
remove paper lint, ink solids, or ammonium ions from the waste wash water. 
It has been found that use of flexographic press waste wash water, alone 
or in combination with corrugator press waste wash water, in the process 
of the present invention has little or no effect on the gelatinization 
temperature or gel characteristics of corn starch adhesives. Additionally, 
it has been found that any adverse effect that the use of flexographic 
press waste wash water may have on viscosity can be readily compensated 
for by small reductions in the amount of carrier starch in the adhesive 
formulation. In practice, an aqueous medium comprising about 50% untreated 
flexographic waste wash water and about 50% fresh water has been used 
successfully to prepare starch based adhesives in accordance with the 
present invention. 
Referring again to the drawing, there is depicted schematically an 
equipment train and process flow diagram for carrying out the method of 
the present invention. The primary system components are the adhesive 
preparation tank 10 and its companion holding tank 20, a sodium hydroxide 
supply tank 40, a first starch feed bin 50, a second starch feed bin 60, a 
borating additive feed bin 70, a first waste wash water collection tank 
80a, second waste wash water collection tank 80b, and a main make-up water 
supply tank 90. The first waste wash water collection tank 80a serves as a 
holding vessel for waste wash water from the periodic cleaning of the 
flexographic printing press 25, while the second waste wash water 
collection tank 80b serves as a holding vessel for waste wash water from 
the periodic cleaning of the corrugator 35. 
To form the aqueous medium to be used in preparing the starch adhesive in 
accordance with the method of the present invention, valve 92 is opened to 
admit fresh water 3, typically tap water, into the main water tank 90, 
while valves 82a and 82b are opened and pumps 84a and 84b activated to 
transfer waste wash water 5 from collection tank 80a and waste wash water 
7 from collection tank 80b to the main water tank 90. Preferably, the 
valves 82a, 82b and 92 are opened and closed so as to provide a mixture of 
water in the main water tank 90 which is about one-half fresh water and 
one-half recycled, i.e., waste wash water. By selectively controlling the 
valves 82a and 82b and their associated pumps 84a and 84b, the make-up of 
the recycled wash water supplied to tank 90 may be varied from 100% 
flexographic printing press wash water 5 to 100% corrugator wash water 7 
or any combination therebetween, although the recycled wash water most 
typically comprises about equal parts of flexographic printing press wash 
water 5 and corrugator wash water 7. 
The preparation of the adhesive in accordance with the method of the 
present invention is a batch-type process. To initiate the preparation of 
a batch of adhesive, water supply valve 32 is opened and pump 34 activated 
to transfer a controlled amount of mixed water 9 from the main supply tank 
90 into the preparation tank 10. Most advantageously, the preparation tank 
10 is mounted on weighing means such as load cells 110 for monitoring the 
weight of the tank 10 and its contents. The load cells 110 generate a 
signal indicative of the collective weight of the tank 10 and its contents 
and transmit that signal to a controller 120 which is in operative 
communication with water supply valve 32 and water supply pump 34. When a 
preselected desired amount of water 9 has been supplied to the preparation 
tank 10, as indicated by the increasing weight detected by the load cells, 
the controller 120 closes valve 32 and deactivates pump 34 to terminate 
the flow of mixed water 9 into the tank 10. As the make-up water 9 passes 
from the main supply tank 90 to the preparation tank 10, it traverses heat 
exchanger 96 wherein the make-up water 9 passes in heat exchange 
relationship with a heating medium 95, typically steam, to heat the 
make-up water 9 to a desired temperature, typically ranging from 
100.degree. F. to 105.degree. F. 
Provision is also made for fresh water 3 to be added directly to the 
preparation tank 10 in the event that the operator desires to use all 
fresh water or a water mix having a greater amount of fresh water than in 
the mixed water available from the main supply tank 90. In such a case, 
the operator may either manually open valve 98 or direct the controller 
120 to open valve 98 to introduce fresh water 3 directly into the 
preparation tank 10 and again closes valve 98 to terminate the flow of 
fresh water 3 directly into the preparation tank 10. Any fresh water 3 
supplied directly to the tank 10 would also generally be preheated to the 
desired temperature, typically ranging from 100.degree. F. to 105.degree. 
F. 
Once the desired amount of water, typically about one-half of the total 
water in the adhesive formulation, has been introduced into the tank 10, 
the controller activates a rotary valve feeder 52 operatively associated 
with starch bin 50 to feed a first portion of starch 55 into the 
preparation tank 10 for admixing with the water therein. Again by 
monitoring the weight of the tank 10 and its contents, the controller 120 
will sense when the desired amount of starch has been introduced into the 
tank 10 and thereupon deactivate the rotary valve feeder 52 thereby 
terminating the flow of starch into the tank 10 from the bin 50. The 
starch 55 in the bin 50 is typically a speciality starch such as modified 
corn starch rather than raw starch. In either case, the starch in bin 50 
is most advantageously in a dry powder form. 
After the correct amount of this first portion of starch 55 has been 
introduced into the tank 10, valve 42 is opened and pump 44 activated to 
meter sodium hydroxide into the preparation tank 10 from supply tank 40. 
The flow of sodium hydroxide 45 is carefully monitored by a mass flow 
meter 44 disposed in the supply line through which the sodium hydroxide 45 
passes and operatively associated with the controller 120. Once the 
desired amount of sodium hydroxide is introduced into the tank 10, the 
controller 120 closes the valve 42 and deactivates pump 44 to terminate 
the flow of sodium hydroxide into the tank 10. Typically, the sodium 
hydroxide is supplied to the tank 10 as a 50% aqueous sodium hydroxide 
solution. 
As the sodium hydroxide solution 45 is introduced into the preparation tank 
10, the mixing means 30 is activated to promote thorough and efficient 
high shear vortex mixing of the sodium hydroxide with the starch and water 
in the tank 10. Thorough and efficient mixing is required as the sodium 
hydroxide serves to chemically cook the starch to form a cooked starch 
slurry, commonly referred to as the carrier portion of the adhesive 
formulation. 
After the introduction of sodium hydroxide solution has ceased, the starch 
slurry is subjected to further high shear vortex mixing action via mixing 
means 30 for a period of about one minute before the introduction of 
borating additive 75 is initiated. To supply borating additive, typically 
borax or boric acid in dry powder form, to the preparation tank 10, a 
volumetric screw feeder 72 operatively associated with the bin 70 is 
activated by the controller 120 to controllably feed a predetermined 
amount of borating additive into the preparation tank 10. The mixing means 
30 remains activated during the feeding of the borating additive into the 
tank 10 to ensure rapid mixing of the borating additive into the cooked 
starch slurry. As noted previously, the borating additive serves to 
stabilize the viscosity of the cooked starch slurry. 
The mixing means 30 remains activated for a period of about 11/2 minutes to 
continually subject the borated cooked starch slurry to a high shear 
vortex mixing action before a second portion of water is introduced into 
the tank 10 to dilute the borated cooked starch slurry prior to addition 
of the final ingredient of the adhesive formulation, which is additional 
starch, typically raw starch, from bin 60. To introduce this dilution 
water into the preparation tank 10, water supply valve 32 is again opened 
and pump 34 activated to transfer a controlled amount of mixed water 9 
from the main supply tank 90 into the tank 10. Again the mixed water 9 is 
desirably preheated to a temperature, typically 100.degree. F. to 
105.degree. F., before introduction into the tank 10. When the desired 
amount of dilution water has been added to the borated cooked starch 
slurry, the valve 32 is closed and the pump 34 deactivated to terminate 
the flow of mixed water 9 from the main water supply tank 90. 
Upon termination of the flow of dilution water into the tank 10, the 
controller 120 activates the rotary valve feeder 62 operatively associated 
with the second starch bin 60 to feed a second portion of starch 65, 
typically raw corn starch, into the preparation tank 10 for admixing with 
the diluted, borated cooked starch slurry therein to yield the finished 
starch adhesive. Again by monitoring the weight of the tank 10 and its 
contents, the controller 120 will sense when the correct amount of 
additional starch 65 has been introduced into the tank 10 and thereupon 
deactivate the rotary valve feeder 62 thereby terminating the flow of 
starch into the tank 10 from the bin 60. 
The mixing means 30 remains activated during the introduction of the 
dilution water and the second portion of starch to continually subject the 
contents of the tank 10 to a high shear vortex mixing action thereby 
ensuring rapid, efficient and thorough admixing of the ingredients. Once 
all the ingredients have been added, the starch slurry is continuously 
agitated for an additional period of time, typically from about 11/2 to 
about 2 minutes, to ensure a uniform finished product. Upon completion of 
this final mixing step, the transfer pump 14 is activated to convey the 
finished starch adhesive into the holding tank 20 from which it is pumped 
on demand to the corrugator 35. 
The method of preparing starch adhesives in accordance with the present 
invention may be advantageously carried out using an automated adhesive 
preparation system, most advantageously, the EXPOMATIC.RTM. automatic 
adhesive preparation system marketed by ABB Sprout-Bauer, Inc. of Muncy, 
Pa. This system utilizes a microprocessor and a programmable logic 
controller operatively associated therewith as a means for controlling the 
overall process, i.e., as controller 120, thereby ensuring introduction of 
the various adhesive ingredients in precisely controlled amounts. The 
EXPOMATIC.RTM. automatic adhesive preparation system also utilizes a high 
shear vortex mixing action to ensure that the ingredients are thoroughly 
and efficiently mixed. 
The method of the present invention may be advantageously controlled by 
maintaining the viscosity of the finished starch adhesive between 
permissible upper and lower viscosity limits. It is well appreciated that 
viscosity of the adhesive controls the rate at which the adhesive is 
absorbed into the paper after its application and prior to gelatinization. 
The higher its viscosity, the more slowly the adhesive is absorbed. To 
ensure proper absorption and applicability, the viscosity should be 
maintained within desirable limits. Typically, the viscosity of the 
finished starch based adhesive should be maintained between a Stein-Hall 
viscosity of 20-25 seconds for low weight board and between a Stein-Hall 
viscosity of 40-72 seconds for heavy weight board. 
Stein-Hall viscosity is an industry standard. A thorough explanation of the 
standard procedures for determining the Stein-Hall viscosity of a starch 
slurry is presented in the aforementioned 1977 TAPPI monograph entitled 
"Preparation of Corrugating Adhesives" at pages 47-50. As a reference 
point, the water at a temperature of 75.degree. F. (23.9.degree. C.) has a 
Stein-Hall viscosity of 15 seconds. 
In practice of the present invention, a viscosity monitor 130, operatively 
associated with the storage tank 20, monitors the viscosity of the 
finished starch adhesive in the storage tank 20. The viscosity monitor 130 
senses the viscosity of the finished starch adhesive and generates a 
signal indicative thereof which is transmitted to the controller 120 
wherein the sensed viscosity signal is compared to an upper viscosity 
limit set point and a lower viscosity limit set point. The upper viscosity 
limit set point represents a preselected upper permissible viscosity for 
the finished starch adhesive based on its subsequent usage and the lower 
viscosity limit set point represents a preselected lower permissible 
viscosity for the finished starch adhesive based on its subsequent usage. 
If the sensed viscosity moves out of the range of permissible viscosity 
defined between the preselected upper and lower set points, the controller 
120 adjusts the formulation of the batch of starch adhesive it is then 
preparing to return the viscosity of the starch adhesive into the 
permissible range. For instance, if the sensed viscosity falls below the 
lower viscosity limit set point, the controller 120 responds by increasing 
the amount of starch introduced into the preparation tank 10. This may be 
accomplished by increasing either the first portion of starch or the 
second portion of starch added to the preparation tank 10 or both. Most 
advantageously, the additional starch is added in the first portion of 
starch which is used to produce the cooked carrier starch portion of the 
formulation. 
On the other hand, if the sensed viscosity of the finished starch adhesive 
in storage tank 20 rises above the preselected upper viscosity limit set 
point, the controller 120 responds by increasing the amount of aqueous 
medium introduced into the preparation tank 10. This may be accomplished 
by increasing either the first portion of aqueous medium or the second 
portion of aqueous medium introduced into the preparation tank 10 or both. 
In either case, the amount of aqueous medium may be increased simply by 
introducing more mixed water 9 into the formulation or by introducing 
fresh water 3 directly into the preparation tank 10.