Adhesive compositions comprising water glass, an oligosaccharide, and a mono-, di- or tri-saccharide

The invention pertains to adhesive compositions comprising water glass, at least one oligosaccharide with more than three saccharide units, and at least one mono-, di- or tri-saccharide. Preferably, the oligosaccharide is a low-molecular weight dextrin. Such compositions demonstrate not only a high curing rate and a good wet tack, but also an excellent storage stability. The compositions are useful as a glue or sizing agent. When they are used as a glue, improved crush values of the finished products are observed.

FIELD OF THE INVENTION 
The present invention pertains to adhesive compositions for paper, 
cardboard, and other paper or paper-like products that comprise water 
glass, at least one oligosaccharide in a concentration of at least 2% by 
weight on the total composition, and a third component. 
BACKGROUND OF THE INVENTION 
There is a demand for adhesives, especially of the kind used for cementing 
or sizing cardboard and paper, with an increased dry solid weight content 
and good storage stability. An increased dry solid weight content will not 
only result in faster curing rates but also leads to reduced water uptake 
by the substrates to be cemented. Typically, fillers are added to increase 
the dry solid weight content. However, these fillers reduce the "wet tack" 
and the curing rate. Moreover, such formulations often are not storage 
stable at ambient temperature and have a too high viscosity for normal 
processing. The poor storage stability typically manifests itself in the 
floating out of one or more of the ingredients. In the case of known water 
glass-dextrin products, very often the dextrin floats out. Also, the use 
of solid fillers in the formulation is less desired, because such a solid, 
especially when used in a high quantity, may settle during storage and 
because it may affect the equipment. Since it often is an abrasive, it may 
for instance cause an increased wear of the pumps. 
Moreover, there is a need for cemented articles with a higher crush value 
than is presently obtained when, for instance, plain water glass is used 
as the adhesive. Such higher crush values will allow the use of 
thinner-walled articles, with attendant savings. 
Therefore, there is still a need for new water glass based adhesive 
compositions with improved properties. 
It is noted that U.S. Pat. No. 3,767,440 discloses a composition comprising 
water glass, dextrin, and a clay slurry. It is stated that known 
formulations containing water glass and more than 0.5% of dextrin, as in, 
for instance, U.S. Pat. No. 3,343,691, are not storage stable. This 
reference teaches to use 4.5-12 % by weight of a clay slurry in the 
formulation to improve the storage stability. As mentioned above, such a 
high qauntity of a solid filler is not desired. It is not disclosed or 
suggested to use a composition comprising a mono-, di- and/or 
tri-saccharide to improve the performance and the storage stability. 
SUMMARY OF THE INVENTION 
As the present invention generally relates to a paper adhesive composition 
comprising water glass, at least one oligosaccharide in a concentration of 
at least 2% by weight on the total composition, and a third component, 
characterized in that the third component is at least one mono-, di- 
and/or tri-saccharide.

The invention is illustrated by the following examples 
EXPERIMENTAL 
Materials used 
Water glass 38/40, with a density of 1,35-1,38 kg/l, supplied by Akzo-PQ 
Silica Vof 
Low-molecular weight dextrin type AVEDEX.RTM. 28 La 21, ex Avebe 
Sucrose ex CSU (Centrale Suiker Unie) with a purity of 99.95% 
All other chemicals were technical grade products of Baker. 
Procedures 
1. The paper stripping energy is determined with the aid of a 
STROHLEIN.RTM. Adhesion Tester, which procedure is recognized by the 
Fipago (Federation Internationale des Fabricants de Papier Gommes). The 
value for the stripping energy depends on the type of paper used in the 
tests and on the experimental conditions, like temperature, humidity, and 
the thickness of the glue layer. The values as presented throughout this 
document were determined as follows: 
The test liner, being the paper attached to the base, was of the "testing 
paper 8283" type and can be obtained from Retsch (NL). The paper on the 
pendulum was of the MG-kraft type and supplied as "Velenhendaye S (70 g)" 
by Gascoinge (FR). The smooth side of the MG-kraft paper is cemented to 
the test liner with 80 g.m.sup.- 2 of adhesive composition. The dimensions 
of the test liner were: length 100 mm, width 60 mm. The dimensions of the 
MG-kraft paper were: length 300 mm, width 30 mm. The test conditions were: 
temperature 23.degree. C. and relative humidity 50%. For reference 
purposes, a standard sodium water glass (38/40 water glass) with a 
specific gravity of 1,38-1,41 kg/l, containing about 9,0% w/w Na.sub.2 O 
and about 29,6% w/w SiO.sub.2, gave a stripping energy of 0.15-0.20 J 
under the conditions used. 
2. The adhesive compositions were produced as follows: 
2.1 A solution of dextrin and specified pH controlling agent in water was 
made by mixing these ingredients in the amounts as defined below, and 
subsequent dissolution at 85.degree. C. 
2.2 In a separate vessel, the mono-, di- and/or tri-saccharide(s) were 
dissolved in the water glass at a temperature of 30.degree. C. 
2.3 The solution of 2.1 was combined with the solution of 2.2. 
2.4 If so desired, a little water was added to control the viscosity. 
Example 1 
A dextrin solution was made using 3 kg water, 11.25 kg dextrin, and 0.75 kg 
potassium carbonate. Using this dextrin solution in combination with a 
solution of 74 kg water glass 38/40, 10 kg sucrose, and 1 kg NaOH gave an 
adhesive composition according to the invention. 
The wet tack of this adhesive composition was 0.16 J, while after 45 
seconds in the adhesion test a paper stripping energy (PSE45) of 0.70 J 
was obtained. The viscosity of the adhesive composition was 500.+-.100 
mPa.s at 20.degree. C., the dry solid weight content was 53.0.+-.1.5%, and 
the pH was 11.5. This adhesive composition was storage stable for more 
than six months. 
Comparative Examples A-C 
In these examples, various amounts of sucrose were dissolved in 38/40 water 
glass. Oligosaccharides were not used. The following results were 
obtained: 
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Sucrose Wet tack PSE45 Viscosity 
Example (% w/w) (J) (J) (mPa .multidot. s) 
______________________________________ 
A 0 0.09 0.14 110 
B 2 0.09 0.08 130 
C 9 0.14 0.36 170 
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Formulations with a higher sucrose level did not solidify in an acceptable 
time span, due to water retention.