A cold-setting starch adhesive comprising the mixture of three different types of corn starch having widely different properties, i.e., high amylose corn starch having an amylose content of at least 50%, ordinary corn starch and waxy corn starch, in specific proportions. The adhesive shows excellent properties due to the effective combination of the outstanding properties of the individual types of starch.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a cold-setting starch adhesive which is suitable 
for use in the manufacture of corrugated fibreboard. 
2. Description of the Prior Art 
Starch adhesive has been commonly used in the manufacture of corrugated 
fibreboard. Known starch adhesives generally consist mainly of 
ungelatinized starch paste. Thus, they are used by Stein-Hall process. 
That is, after the starch paste is firstly gelatinized to sticky paste by 
steam heating and treatment with caustic soda solution, it is successively 
applied to the tips of corrugated medium to be bonded to the liner to form 
corrugated fibreboard, and subsequent heating of the corrugated fibreboard 
vaporize the water from the paste to dryness to complete the setting. 
The heat energy consumed by the corrugating operation of Stein-Hall process 
occupies the major part of the total energy consumption in corrugated 
fibreboard manufacturing plants. If the heating procedure can be 
eliminated from the corrugating operation, it will contribute to energy 
saving in corrugated fibreboard manufacturing plants. It has, therefore, 
been of great interest to the corrugated fibreboard industry to develop a 
cold-corrugating process which does not require any heating procedure at 
the corrugating step of corrugated fibreboard. 
Some hot-melt adhesives obtained as petrochemical product is known as being 
cold-setting. They, however, have the following disadvantages. The raw 
materials of the hot-melt adhesives are becoming less available because of 
the high price of petroleum. Used corrugated fibreboard made by employing 
a hot-melt adhesive is difficult to recover and reuse. Accordingly, it has 
been strongly desired to develop a cold-setting corn starch adhesive for 
use in the manufacture of corrugated fibreboard. 
Certain properties are required for a cold-setting corn starch adhesive 
which is to be used for bonding in the manufacture of corrugated 
fibreboard without heating procedure. That is, the paste solution must 
have high solid content, so that it may contain only a small quantity of 
water to be vaporized. It must be able to gel rapidly, as it is required 
to set immediately after the application to the fibreboard surfaces to be 
bonded together. 
Other properties are also required for an adhesive for use in the 
manufacture of corrugated fibreboard, namely, during the manufacture of 
corrugated fibreboard, production speed of as high as possible is desired 
on a corrugator in normal operation, while it must be slowed down when a 
small lot of products is manufactured, or at the beginning or the end of 
the operation. It is, therefore, necessary to employ an adhesive having a 
constant gluing ability irrespective of the production speed, whether it 
may be high or low. This requirement is nowadays of increasing importance, 
since the operation speed on a corrugator is as high as 250 meters per 
minute. 
However, ordinary corn starch adhesives, when they are used as 
cold-corrugating adhesives, tend to gel so slowly that unsatisfactory 
setting appears if the operating speed of the corrugator is increased, and 
even a slight external force can cause the separation of the glued 
surfaces when, for example, the corrugated fibreboard is cut to a 
prescribed size. Therefore, when they are used as cold-corrugating 
adhesives in the process of manufacturing corrugated fibreboard, the 
efficiency of the process is far inferior as compared when they are used 
in Stein-Hall process. 
Japanese Laid-Open Patent Specification No. 32570/1981 discloses a 
cold-corrugating adhesive for corrugated fibreboard having improved 
glueability at high production speed. This adhesive consists mainly of 
high amylose corn starch instead of ordinary corn starch which is the main 
component of all the known starch adhesives. High amylose corn starch is a 
starch prepared from specialty corn created by selective breeding. It 
contains at least 50% of amylose, while ordinary corn starch contains only 
about 25% of amylose. 
Because of its high amylose content, high amylose corn starch has a variety 
of outstanding properties, for example: 
(a) It is hard to be gelatinized under normal conditions; 
(b) it can form high solid paste; 
(c) it is highly susceptible to retrogradation; 
(d) it forms strong film; and 
(e) it has high glueability. 
Some of these properties of high amylose corn starch make it a very 
suitable substance which can impart rapid glueability to cold-corrugating 
adhesive for use in the manufacture of corrugated fibreboard. As already 
pointed out, paste prepared from cold-corrugating starch adhesive must 
have high solid concentration when it is used at higher operating speed so 
that it may contain only a small amount of water to be vaporized, and must 
be capable of gelling rapidly after the application to the fibreboard 
surfaces to be bonded together. These requirements are fully satisfied by 
the properties (b) to (e) of high amylose corn starch. 
The high amylose corn starch adhesive disclosed in Japanese Laid-Open 
Patent Specification No. 32570/1981 is, thus, partly satisfactory for 
application at higher operating speed. It, however, retrogrades and dries 
too rapdily, and can retain only a small amount of water. Consequently, if 
the operating speed is low, it is likely to solidify on the applicator 
roll, or on the fluit tip of the corrugating medium before bond it with 
the liner. Thus the adhesive from high amylose corn starch cannot show 
satisfactory glueability outside of only a narrow range of operating 
speeds. The use thereof for application at lower operating speed is likely 
to result in an increased percentage of defective bond. 
Another problem resides in the quality of the material which is available 
for making corrugated fibreboard. Recent shortage of pulp resources makes 
it difficult to obtain good pulp, and necessitates the use of fibreboard 
material of lower strength for making corrugated fibreboard. Synthetic 
resins, or other reinforcing agents are often added to the material in 
order to compensate the deficient strength. Synthetic resins are sometimes 
added purely for the purpose of producing reinforced liner or medium 
having improved strength irrespective of the quality of the pulp. The 
adhesive prepared from high amylose or ordinary corn starch is, however, 
very unsatisfactory for gluing any such resin-reinforced liner or medium. 
Under these circumstances, it has hitherto been considered impossible to 
produce from starch a cold-corrugating adhesvie for corrugated fiberboard 
which shows high glueability both at higher and lower operating speeds. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a cold-corrugating starch 
adhesive which is sutiable for corrugated fibreboard. 
It is another object of this invention to provide a cold-corrugating starch 
adhesive which is satisfactorily applicable both at higher and lower 
operating speeds, and which does not require heating during application, 
and can, therefore, contribute to energy saving in the manufacture of 
corrugated fibreboard. 
It is still another object of this invention to provide a cold-corrugating 
starch adhesive which shows satisfactory glueability for any type of 
material employed in the manufacture of corrugated fibreboard. 
It is a further object of this invention to provide a water-resistant, 
energy-saving adhesive which is satisfactorily applicable both at higher 
and lower operating speeds, and which does not require heating during 
application. 
DETAILED DESCRIPTION OF THE INVENTION 
This invention provides a cold-corrugating starch adhesive which is 
satisfactorily applicable both at higher and lower operating speeds for 
making corrugated fibreboard by a corrugator. 
The inventors of this invention have discovered that the combined use of 
high amylose corn starch, ordinary corn starch and waxy corn starch 
surprisingly produces a cold-corrugating starch adhesive suitable for 
corrugated fibreboard, which is satisfactorily applicable at lower 
operating speed, while retaining the rapid glueability which is 
characteristic of high amylose corn starch. 
Thus, this invention provides a cold-corrugating starch adhesive in the 
form of a hot aqueous high solid paste of gelatinized starch which 
comprises 20 to 80% by weight of high amylose corn starch having an 
amylose content of at least 50%, or any modified form thereof, 10 to 79% 
by weight of ordinary corn starch or any modified form thereof, and 1 to 
10% by weight of waxy corn starch (total is 100% by weight). 
If the proprotion of high amylose corn starch is less than 20% by weight, 
no satisfactory glueability is obtained at higher operating speed, while 
no satisfactory glueability is obtained at lower speed if less than 10% by 
weight of ordinary corn starch is employed. 
The most important feature of this invention resides in the fact that the 
ashesive is endowed with improved glueability at lower operating speed, 
while retaining high glueability at higher operating speed by the 
incorporation of waxy corn starch into a mixture of high amylose corn 
starch and ordinary corn starch. 
Waxy corn starch does not contain amylose, and consists solely of 
amylopectin. Therefore, it has a number of properties which are different 
from these of high amylose corn starch. For example, it is (a) easy to be 
gelatinized, (b) higher sticky, and (c) capable of holding large amount of 
water. The high glueability of the adhesive of this invention at lower 
operating speed is due to the presence of waxy corn starch. It provides a 
starch paste with an improved water-holding capacity during gluing at 
lower speed and it prevents any undersirable solidification of the paste 
on the applicator roll, or drying or solidification of the paste before 
the completion of the gluing speration. 
The adhesive of this invention containing waxy corn starch is 
satisfactorily applicable also to the aforementioned resin-reinforced 
liner or medium as opposed to any known adhesive not containing waxy 
starch. 
If the proportion of waxy corn starch is less than 1% by weight, however, 
it is difficult to expect the improved glueability of the adhesive at 
lower gluing speed, while a paste containing more than 10% by weight of 
waxy corn starch is too stringy to be applied uniformly by rolls. 
It is surprising that the advantages of the three different types of starch 
in the adhesive of this invention exhibit themselves to the maximum extent 
without cancelling one another. This is only possible as a result of the 
combination of the three different types of starch. Such adhesive having 
high glueability both at higher and lower operating speeds as that of the 
present invention would not be obtained from the mixture of only high 
amylose and waxy corn starches, nor from the mixture of high amylose and 
ordinary corn starches in any proportion. 
A method for preparing the cold-corrugating starch adhesive may comprise 
adding water to a mixture of high amylose, ordinary and waxy corn 
starches, and if required, an oxidizing agent such as persulfate or 
perborate; gelation promotor such as boric acid, borax or a sulfite; pH 
adjustor such as sodium hydroxide, or the like, mixing them together, and 
heating the resulting mixture to the temperature of between 80.degree. C. 
and 100.degree. C. by conventional method, e.g. by using a cooking device 
such as jet cooker, autoclave or Onlator (indirect heating cooker) to give 
a hot high solid paste of gelatinized starch with a viscosity of between 
500 and 1500 cps and having a solid content of 20-50% by weight. This 
paste is applied to the fibreboard surfaces to be glued together, and them 
immediately allowed or forced to cool, whereby the paste sets rapidly to 
produce strong adhesion. 
The adhesive of this invention may contain, as high amylose corn starch 
having an amylose content of at least 50%, any modified form thereof 
obtained by oxidizing, etherifying, esterifying, or otherwise treating the 
starch in a known manner. Such modification of high amylose corn starch by 
oxidation, etherification, esterification, or the like makes it easier to 
form a gelatinized paste, and to prepare a more homogeneous and stable 
paste. 
The modification of ordinary corn starch by a known method such as 
crosslinking, etherification or the like is also useful for obtaining an 
adhesive of improved glueability in the form of a short stringy paste 
having an improved water-holding capacity. Waxy corn starch may likewise 
be modified, if required. 
The adhesive of this invention may shrink when it sets. In order to prevent 
such shrinkage, it is possible to add any known inorganic or organic 
filler, such as bentonite, clay, calcium carbonate, ground wood powder, 
walnut shell flour or coconut shell flour, so that a stronger adhesive 
layer may be obtained. The filler may be added in the amount of 1 to 100%, 
preferably 2 to 20%, by weight based on the starch, depending on the 
filler which is employed. The smaller amount less than 1% is not 
effective, while the addition of greater than 100% is likely to bring 
about disadvantages, such as lower glueability. 
If water resistance is required for the adhesive of this invention 
formaldehyde resin solution can be incorporated. It is possible to use 
urea-formaldehyde resin solution, melamine-formaldehyde resin solution, 
resorcinol-formaldehyde resin solution, or ketone-formaldehyde resin 
solution, or a mixture or co-condensation resin solution thereof, or a 
solution of any such resin modified with acetoguanamine, thiourea, 
ethylene urea, phenol, cresol, ethylenediamine, diethylenetriamine, or the 
like. 
Such formaldehyde resin solution is usually employed in the quantity of 5 
to 50% by weight based on the total starch amount, considering the effect 
and the expense of the resin solution. More preferably, it is employed in 
10 to 25% by weight. The formaldehyde resin solution, when employed in the 
prescribed range of quantity, imparts outstanding water resistance to the 
adhesive of this invention without impairing its glueability at both 
higher and lower operating speeds. It may be added into the high solid 
gelatinized paste prepared as hereinabove described, after the pH of the 
paste has been adjusted to a range of 4 to 7. 
The water-resistant adhesive thus prepared in the form of a hot high solid 
paste of gelatinized starch is particularly suitable for use in the 
manufacture of water-resistant corrugated fibreboard. The adhesive is 
applied to the fibreboard surfaces to be glued together, and after the 
surfaces have been glued together, the adhesive is immediately allowed or 
forced to cool, whereupon it sets rapidly, and corrugated fibreboard with 
strong, water-resistant adhesion is obtained. 
The cold-setting starch adhesive of this invention shows outstanding 
glueability at both higher and lower operating speeds. As it can 
accomplish strong adhesion without heating during the corrugating 
operation, it contributes greatly to reducing the consumption of heat 
energy in corrugated fibreboard manufacturing plants. It does not cause 
any appreciable inconvenience in the recovery and reuse of used corrugated 
fibreboard, as compared to petrochemical hot-melt adhesives. 
Although the adhesive of this invention is particularly useful in the 
manufacture of corrugated fibreboard, it is, of course, equally applicable 
to ordinary paper, cloth, wood, plastics, inorganic material, or any other 
material in general.

The invention will now be described with reference to examples thereof. 
EXAMPLE 1 
Sixty parts by weight of high amylose corn starch having an amylose content 
of 70%, 35 parts by weight of ordinary corn starch, and 5 parts by weight 
of waxy corn starch were suspended in 186 parts by weight of water. Added 
into the suspension were 2 parts by weight of sodium persulfate, 0.5 part 
by weight of sodium sulfite, 2 parts by weight of boric acid and 1 part by 
weight of sodium hydroxide. Gelatinized paste was formed from the 
resulting mixture by a continuous paste forming apparatus (Onlator of 
Sakura Seisakusho, Japan). 50% by weight aqueous solution of sodium 
hydroxide was added into the paste to adjust the pH value to 9.0, whereby 
there was obtained a cold-setting starch adhesive in the form of a 
gelatinized paste having a temperature of about 90.degree. C. and a solid 
content of about 33% by weight. 
The glueability of the adhesive was tested by applying it to the 
single-face of the fibreboard by a testing corrugator both at a low 
operating speed of 4 m/min. and at a high operating speed of 20 m/min. For 
this test, the hot high solid gelatinized paste was maintained at a 
temperature of about 90.degree. C., and applied to the flute tip of the 
corrugating medium at an application rate of about 5 g/m.sup.2 (dry 
weight). After a kraft liner had been placed on the corrugating medium, 
cold air was blown against the paste to cool and set it, whereby glued 
corrugated fibreboard was obtained. K liner-280 of Honshu Paper Co., 
Japan, SCP 125 of Honshu Paper Co. and MM 180 of Honshu Paper Co. were 
used as the liner, the corrugating medium and the reinforced corrugating 
medium respectively. 
From this fibreboard, test pieces of 8.times.5 cm were cut out and tested 
for adhesion strength by a compression testing machine in accordance with 
JIS (Japanese Industrial Standards) Z-0402. The results, as well as those 
of the other examples, are shown in TABLE 1 below. 
EXAMPLE 2 
An aqueous suspension was prepared from 350 g of high amylose corn starch 
having an amylose content of 70% in 400 ml of water at 40.degree. C. 3% 
aqueous solution of sodium hydroxide was added into the suspension to 
adjust the pH value to 11.5. Into this starch suspension was further added 
28 ml of 50% aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium 
salt. The resulting solution was stirred for four hours at 40.degree. C. 
After hydrochloric acid had been added into the solution to adjust the pH 
value to 6.5, the solid content of the solution was separated and washed 
with water, and dried, whereby cationic high amylose corn starch was 
obtained. 
The procedures of EXAMPLE 1 were repeated, except for using 60 parts by 
weight of the cationic high amylose corn starch, 35 parts by weight of 
commercially available etherified ordinary corn starch (hydroxyethyl corn 
starch 5-B of Nippon Shokubai Kagaku Kogyo, Japan), and 5 parts by weight 
of waxy corn starch, and there was obtained a cold-setting starch adhesive 
in the form of a gelatinized paste of about 90.degree. C., and a 
concentration of about 33% by weight. 
The adhesive was used to make corrugated fibreboard in accordance with the 
procedures described in EXAMPLE 1, and the adhesion strength of the 
fibreboard was tested as described in EXAMPLE 1. 
COMATIVE EXAMPLE 1 
The procedures of EXAMPLE 1 were repeated to prepare a hot high solid 
gelatinized paste, except for using only ordinary corn starch having an 
amylose content of 24%, and corrugated fibreboard was made from this paste 
to test its adhesion strength as in EXAMPLE 1. 
COMATIVE EXAMPLE 2A 
The procedures of EXAMPLE 1 were repeated to prepare a hot high solid 
gelatinized paste, except for using 100 parts by weight of high amylose 
corn starch of an amylose content of 70%, and corrugated fibreboard was 
made from this paste to test its adhesion strength as in EXAMPLE 1. 
COMATIVE EXAMPLE 2B 
The procedures of COMATIVE EXAMPLE 2A were repeated, except for using 60 
parts by weight of high amylose corn starch of an amylose content of 70% 
and 40 parts by weight of ordinary corn starch, while using no waxy corn 
starch. 
The results of the foregoing examples are shown in TABLES 1 and 2 below. 
TABLE 1 shows the results of the adhesion strength tests conducted on 
corrugated fibreboard prepared by employing SCP 125 of Honshu Paper Co. as 
the corrugating medium, while TABLE 2 shows the test results on corrugated 
fibreboard prepared by employing MM 180 of Honshu Paper Co. as the 
reinforced corrugating medium. 
TABLE 1 
______________________________________ 
Adhesion strength (kg) 
Corrugated fibreboard 
Corrugated fibreboard 
obtained at an operating 
obtained at an operating 
speed of 4 m/min. 
speed of 20 m/min. 
______________________________________ 
Example 1 
19.3 19.8 
(invention) 
Example 2 
19.6 20.4 
(invention) 
Comparative 
14.3 Gluing impossible 
Example 1 
Comparative 
17.1 19.2 
Example 2A 
Comparative 
16.7 18.8 
Example 2B 
______________________________________ 
NOTE: 
The testing machine had a variable speed of 0 to 20 m/min. 
TABLE 2 
______________________________________ 
Adhesion strength (kg) 
Corrugated fibreboard 
Corrugated fibreboard 
obtained at an operating 
obtained at an operating 
speed of 4 m/min. 
speed of 20 m/min. 
______________________________________ 
Example 1 
18.1 17.9 
(invention) 
Example 2 
19.8 18.4 
(invention) 
Comparative 
10.4 Gluing impossible 
Example 1 
Comparative 
12.6 14.1 
Example 2A 
Comparative 
12.1 13.4 
Example 2B 
______________________________________ 
As is obvious from the test results shown in TABLES 1 and 2, the adhesives 
of this invention showed excellent glueability at both high and low 
operating speeds. 
On the other hand, the conventional adhesive of COMATIVE EXAMPLE 1 
comprising only ordinary corn starch was found inapplicable for operating 
at a high speed. The high amylose corn starch adhesive of COMATIVE 
EXAMPLE 2A was very poor in glueability at a low speed. 
The adhesive of COMATIVE EXAMPLE 2B comprising high amylose corn starch 
and ordinary corn starch was inferior in glueability at both high and low 
speeds to the adhesive of this invention. The adhesive of COMATIVE 
EXAMPLE 2B was also found to show an undesirable variation in glueability 
depending on the material from which corrugated fibreboard was formed. 
EXAMPLE 3 
A gelatinized paste was prepared in accordance with the procedures in 
EXAMPLE 1. After 50% by weight aqueous solution of sodium hydroxide had 
been added to this paste to adjust the pH value to 6.0, 20 parts by weight 
of a urea resin solution (UW-062 of Hohnen Oil Co., Japan) were added into 
the paste, and mixed to obtain a cold-setting, water-resistant starch 
adhesive in the form of a gelatinized paste of a temperature of about 
90.degree. C. and a solid content of about 35% by weight. 
The glueability of the adhesive was tested by applying it to the 
single-face of the fibreboard by a testing corrugator both at a low 
operating speed of 4 m/min. and at a high operating speed of 20 m/min. For 
this test, the hot high solid gelatinized paste was maintained at a 
temperature of about 90.degree. C., and applied to the flute tip of the 
water-resistant corrugating medium (SSCP 125 of Honshu Paper Co.) at an 
application rate of about 10 g/cm.sup.2 (dry weight). After a 
water-resistant liner (SK 280 of Honshu Paper Co.) had been placed on the 
corrugating medium, cold air was blown against the paste to cool and set 
it, whereby corrugated fibreboard was obtained. 
From this fibreboard, test pieces of 8.times.5 cm were cut out and after 
the specimens had been immersed for one hour in water at 20.degree. C., 
they were tested for water-resistant adhesion strength by a compression 
testing machine. The results, as well as those of other examples, are 
shown in TABLE 3 below. 
EXAMPLE 4 
Cationic high amylose corn starch was prepared in accordance with the 
procedures of EXAMPLE 2. A gelatinized paste having a pH value of 7.0 was 
prepared in accordance with the procedures of EXAMPLE 3 from 60 parts by 
weight of the cationic high amylose corn starch, 35 parts by weight of 
commercially available etherified ordinary corn starch (hydroxyethyl corn 
starch 5-B of Nippon Shokubai Kagaku Kogyo, Japan), and 5 parts by weight 
of waxy corn starch. To this paste was added 15 parts by weight of a 
melamine-formaldehyde resin solution ML-044 of Hohnen Oil Co.), and there 
was obtained a cold-setting, water-resistant starch adhesive in the form 
of a gelatinized paste of a temperature of about 90.degree. C. and a 
concentration of about 35% by weight. 
The procedures of EXAMPLE 3 were repeated to made water-resistant 
corrugated fibreboard from the adhesive thus obtained, and to test its 
water-resistant adhesion strength. 
COMATIVE EXAMPLE 3 
The procedures of EXAMPLE 3 were repeated for preparing a hot high solid 
gelatinized paste except for using only ordinary corn starch having an 
amylose content of 24%, and water-resistant corrugated fibreboard was made 
from this paste to test its water-resistant adhesion strength. 
COMATIVE EXAMPLE 4 
The procedures of EXAMPLE 3 were repeated for preparing a hot high solid 
gelatinized paste except for using only high amylose corn starch having an 
amylose content of 70%, and water-resistant corrugated fibreboard was made 
from this paste to test its water-resistant adhesion strength. 
COMATIVE EXAMPLE 5 
The procedures of EXAMPLE 3 were repeated for preparing a hot high solid 
gelatinized paste except that no urea-formaldehyde resin solution was 
employed, and water-resistant corrugated fibreboard was made from this 
paste to test its water-resistant adhesion strength. 
The test results obtained in the foregoing examples are shown in TABLE 3 
below. 
TABLE 3 
______________________________________ 
Water-resistant adhesion strength (kg) 
Corrugated fibreboard 
Corrugated fibreboard 
obtained at an operating 
obtained at an operating 
speed of 4 m/min. 
speed of 20 m/min. 
______________________________________ 
Example 3 
3.85 3.72 
(invention) 
Example 4 
4.29 4.18 
(invention) 
Comparative 
1.70 Gluing impossible 
Example 3 
Comparative 
1.28 3.67 
Example 4 
Comparative 
Separated Separated 
Example 5 
______________________________________ 
NOTE: 
The testing machine had a variable speed of 0 to 20 m/min. 
As is obvious from the results shown in TABLE 3, the water-resistant, 
cold-setting starch adhesive of this invention showed excellent 
water-resistant adhesion both when applied at a high operating speed, and 
at a low operating speed.