|Title of Invention||
A METHOD FOR PREPARING A STEIN HALL ADHESIVE
|Abstract||This invention relates to a method for preparing a Stein Hall adhesive, comprising the steps: '- preparing a carrier portion by gelatinising at least a part of the total starch in the adhesive in an alkaline medium; -diluting the carrier portion with a volume of water; and -adding the remaining secondary starch; wherein in a first step said carrier portion is prepared using part of the alkali, and i~ a second step the carrier portion is diluted with a volume of water, followed by the addition of at least a portion of the secondary starch, characterised in that a high dry substance Stein Hall adhesive, containing betWeen 32 and 45 % dry weight starch solids, is prepared using a single mixing vessel, wherein in the first step said carrier portion is prepared in the single mixing vessel, and in a third step the remaining alkali is added in a diluted form together with the secondary starch.|
Ilie inventioo relates to a method for preparing a Steio Hall adhesive, comprising the steps;
- preparing a carrier portion by gelatinising at least a part of the total stareh in the adhesive in an all^aline medium;
- diluting the carrier portion with s vohmie of water; and
- adding the remaining secundary starch,
wherein in a first step said carrier portion is prepared using part of the alkali, and in a second step the carrier portion is diluted with a volume of water, followed by the addition of at least a portioo of the secondary starch.
The invention fiirther relates to a high dry substance Steia Hall adhesive (also called a high coflcentralion Stdn Hall adhesive or glue) obtained by a such method-Starch based adhesives are well known in the conugated board iodusny. Ajnong the adhesives used, Stein Hall-type adhesives are the most popular.
Stein Hall adhesives are generally known as comprising a carrier portion of the adhesive thai is obtained by gelatinising about 10-20% of the total stand: in the glue using caustic soda. Hie resukant paste is then cooled and diluted with water and the renaining starch is then added as native granular starch Also borax (1,5-2,5%) is added.
Under these circumstances, the ma>dmum total starch concentratioQ in these Stein Hall-type fonnuJations does not surpass 25%, although values up to 30-37% on dry weight basis have been reported. These higher values were obtained when viscosity of the carrier was reduced by means of an oxidation reaction or the like
the disadvantage of these low-concentration adhesivcs is that they contain higher water contents, reduce adhesion speed and retard drying of the adhesive layer in the adhesion step, to addition, higher dry substance adhesives result in reduced energy
consumption because smaller quantities of water need to be evaporated.
Subsequetfly, higher starch concentrations in the ghie are desirable. But, it is also known that, when starch is used as the binding agent, there is a limit to the highest amount of starch that can be used. At lugher amounts of stareh the amount of water becomes insufficient to guarantee the desired adhesion, "R^e the viscosity of the adhesive becomes too high.
High conceatiatioD starch based adhesives hava already been described in the prior art- In IN 160786 a starch based adhesive is described that is composed of a compieteiy gelatinised stards fraction and a partly swollen starch fiacfion, this in a ratiobetween 0,2:100 and 2:1. The adhesive may contain between 10% and 40% dry weight stardi solids. The gelatinised fiacticHi is obtaiaed by heat treaimwit at 95°C or highar, and not via mking with concentrated alkali as in a classic Stein Hall fonnulatioa In feet, h is a no-canier type adhesive to i^ch a gelatinised starch faction is added to improve wet tack of tlie adhesive.
In EP 0 576 221 adhesive conqjositions are disclosed comprising from 15 to 35% by weight stardi solids. A substaiaial quantity of the starch is partially swollen (preferably between 20 and 50%).
EP 0 376 301 describes an adhesive prepared by treating a starch slurry in a jet cooker at a tcn^wrature between 120 and 200°C to obtain a gelatinised diversion. The ungelatinised is then added to this gelatinised di^>ersion. The total starch solids content in tiiis fonnula. as illustrated in the examples, varied between 32 and 40%.
Also in OB 1 571 336, a method is described for the preparation of a starch-based aqueous adhesive. In this method, a carrier portion is prepared of gelatinised
moleculariy dispewed starch at a. solids content from 3 % to 40 % by weight by cooking a stardi slurry using a jet cooker. The carrier portioa is ten tnijced with a siurry of nngelatinized starch. Alkali is provided in The resulting mixture.
The adhesives described in these applications are not typical Stein Hall compositions.
In EP 1 101 809. high dry substance.stardKbased adhesives are described containing at least 40%, piefcrably at Itast 46% dry substance. This fai^ dry sabstance content is realised by the addition of inorganic salts preferably calcium carbonate, to the starch-based adhesive. The starch/finer ratio is preferably at least 60:40. The adhewve can be of the Stein-Hall, no-carrier or ^Boocar-type.
In EP 0 409 240, a hi^i concentration starch slurry adhesive is described comprising between 20 and W/o by weight of starch solids. This adhesive is stabilised through the addition of a gum such as xanthan or rhamsas gum and some sodiuiB hydroxide.
In WO 9850478 high dry substance adhesive compositions are that contain a substantive amount of waler-sohjble alkaline silicate, together with stard;, borax: and sodium hydroxide. Adhesive compositions containing up to 45% solids are disclosed in the examples.
Part of the above-cited prior-art documents are not related to Stein-Hall typo adhesives, such as EP 0 038 627, EP 0 576 221, EP 0 376 301 and EP 0 409 240.
Tte two other documents cited, i.e. BP 1 101 809 and WO 9850478, may comprise Stein Hall-type adhesives, but they differ substantially from standard formulations in that they contain inorganic filler material that contributes to the high dry substance of thcgbe.
In the state of the art, fiirtba- high dry substance Stein HaJl-type adhesives have been disclosed.
in US 3,912,531 high dry substance adhesives of the Steia Hall-type are disclosed containit^ up to 40?^ by weight of starch solids.
However, the disadvantage of this (dnd of high dry substance Stein Hall adhesives is that this is realised by using a fluidity starch having a fluidity between 25 and 90 as the carrier stardi or as part of the carrier starch.
Also EP 0 049 009 discloses high dry substance glues of the Stein Hall-type. The problem underlying this patent document is how to obtain a final high DS ghie whwe the viscosity does not increase strongly and whereby the mixture remains pumpable. £Q feet the ghie must show some storage st^jflity and workable viscosity.
ID the patent document, it is stated that Hgh dry substance gh«s can not be obtained with the conventional techaoJogy for preparing Stein Hall-type adhesives (which have a low dry substance). As described above, the method by Wiidi these kinds of Stein Hall-type ghies arc prepared congjiises preparing the carrier and thereafter diluting it by lowering the alkalinity. When the alkalini^ would not be lowered, the addition of the secundaiy starch would be affected and would result in granule swelHng and viscosity instability.
Howwfflr, if high dry subaance ghies have to be obtained, dilution is becoming insufficient to prevent undesirable swelling. In addition to this, the combination of less diluted carrier and high secondary starch concentration will result in composition that are no longer workable.
The solution to this problem ibst is proposed in the application EP 0 049 009 consists in oxidisins the carrier pc»tioE and then gelatinising the oxidised starch in presence of the necessary amount of sodium hydroxide, thereby reducing the viscosity of the earner to a value which makes it possible to add tlie required sccundary starch. This
sccundary starch is then added to reach a 40VB d.s, glue. It should be emphasised that the carrier starch portion in the glue represents more than 14% of the starch dry substaocc present in the glue.
The disadvantage of this method is that high dry substance glues are obtained with the necessity of using reduced viscosity starches in the carrier fraction.
The reduced viscosity starches referred to in the patent documents of the state of the art typically are fluidity starches or oxidised starches in which the fluidity starches are obtained via chemical or enzymatic degradation.
In US 6,048,391, a process is described for the preparation of a starch based ghit for making conugaJed board. The process is carried out in a system which includes a first and relatively large mixing vessel contairdng a stirrer. A second and smaller mixing vessel is connected to the first mixing vessel via a recirculation path. The second and smajla mixing vess^ contains means for exiting a shearing force ■which is greater than the shearing force eserted in the first and larger misiog vessel. The process is carried out in two steps. In a first step, water and starch are supplied to form a carrier in the first mixing vessel, and then the resulting carrier is transported to the second mixing vessel. Lye is first added in a coacrolled manner in the second mixing vessel to prepare the earner. A second step adds flirther amount of starch, water, borax, and a second shot of lye to the canier while in the small vessel.
The disadvantage of this system is that a supplementary mixing vessel is provided, wherein a circulation loop is introduced, ia this way, a technical more complex and more eKpensive system is provided. Furthermore, the Stdn Hall adhesivea as obtained by this method do not have a high dry substance.
The purpose of the invention is to provide a method for pi^aring a Stein Hall adhesive vAioh doesn't dww the abovementiooed disadvantages.
This purpose is achieved by providing a method for prqjaring a Stein Hall adhesive,
comprising the steps:
- preparing a carrier poitioa by gelatinising at least a part of the total starch in the
ailiiesJve in an alkaline medium;
diluting the carrier portion with a volume of water; and
addJog the remaining secondary starch; wherein in a first step said carrier portion is prepared using part of the alkali, and in a second step the carrier portion is diluted viith a vohime of water, followed by the addition of at least a portion of the secondary starch, wherein a bigh dry substance Staa Hall adhesive is prqnred using a single mixit^ vessel, wherein in the first step said earner portion is prepared in the single mixing vessel, and in a third step the remaining alfcalJ is added in a diluted fonn together with the secondary starch.
to a prefisrred method according to the invention, the addirion of the remaining secundary starch and alkali is perfbnned stepwise.
This has thft advantage that tiie secundary stardi ia not iSrectly subnntted to excessively high alkaline concentrations, thus preventing prwnalure sweilling of the secundary s^^
In a more preferred method accordir^ to the invention, the addition of aikali and starch is done in at least two steps.
In a specific method according to the invention, during the first step, s carrier portion is prepared containing between 2 and 9 % of the total starch content by mixing the starch together with water and alkali until all the starch ha^ gelatinised.
In a more specific method according the invtrfiiJOu, iii Ui£ Erst step, ths slkzli content in the carrier portion is typically less than 2^ of the total amount needed in the adhesive fonnulatioo.
In another specific method according the invention, in the second step the carrier portion is diluted with a volume of water corresponding to 60 to 85 % of the carrier
In a more specific method according the invention, in the second step 50 to 75 % of the secuodary starch is added.
lo a preferred method accorcfing to the iivemioa, after the third step borax is added.
The advantage of this is that initia] tacking is improved and both water reteirtion and peDetration ability of the adhesive is regulated.
The purpose of the invention is firths- achieved by providing a high dry substance St«n Hall adhesive obtained by a method as described above, whereby
- it contains between 32 to 45 % native or stabilised starch;
the ratio carrier starch to secundaiy starch is between 1:50 and 1:1 r it shows a Bauer-viscosity between 21s and 60s; and
- the alkali concentration in the glue is sufficient to provide a SGP of between 45
*C and 53 "C.
In & prefered high dry sjbstancc Stein Hall adhesive according the invention, the native or stabilised stardi is obtained fl^m cereal, tuber or root starches.
The me&od for preparing the glues of the invention comprises several consecutive
« during a first Sep a carrier portiwi is pi^ared containing between 2 to 9 Vo of the total stardi content, by mixing the starch together with water and alkali until aii the eiafiiii haS gcia:tiuiS£d. The iUcwi cc^tcnt ir th; -zsi^rLtT '^r.r^r^n is timi^^aiiv
r" -■ -' -J r-"- "■ J
less than 2/3 of the total amount needed in the ghie formulation;
• during the next step the carrier portion is diluted with a vohime of water coirespondiug to 60 to 85% of the carrier volume, followed by the addition of at least hal^ and at most 75% of the secondary starch.
• in a further step the remaining alkali is thea added in a diluted form together with the remaining secondary stsrcb.
The addition of remaining starch and alkali can be perfonned simultaneously or
stepwise. When addition is perftnned simultaneously, care must be taken that starch
is not submitted directly to alkali.
During the stepwise addition, atkaii is &st added to the mixhire of the &st and the
next step, followed by the addition of the remaining secucdary starch. Stepwise
addition of alkali and starch is preferably done in two or more steps.
Finally borax is added to finish the glue,
Hie high dry sul«tance Stein Hall type adhesives according to the invention have the following properties;
• they contain between 32 to A5% native or stabilised starch,
» the ratio oaniea-starch to secundary starch is between 1:50 to 1:11,
• they show a Bauer-visoosfty between 21 s and 60 s,
• and the alkali concentration in the glue is sufficient to provide a SGP of between 45aod53X.
The native or stabilised starch can be obtained from cereal, tuber or root starches. Typical examples thereof are eg. starches obtained from maize, ■wAeai, barley, potato, tapioca or arrowroot, including the waxy and irigfa amylose type starches. The stabilised starches referred to in the application correspond with starches that have been physically and/or chenucaJly treated in view of obtaining starches that are less sensitive lo alkali at ambient or slightly higher terE^)era£ures. As a result thereof they are not subject to uncontrolled premature swdling and/or gelatinisalion.
The advantage of the high dry substance Stein HaU adhesives according to the invention and produced by the merthod by the inventioa is that there is no necessity to use reduced viscosity starches in the carrier fraction, while the corresponding adhesives sfill do show excellent storage stability, and workable viscosities. They only contain native or stabilised starches Furthermore, a final pumpable high dry substance glue is obtained.
This invention will now be illustrated by tfce following examples which should be considered as being not limiting to the scope of the invention as such and as expressed in the following claims.
A high dry substance glue was prepared ai foilows:
In a 2000 I vessel, first the earner fraction was prepared. Therefore, 16 1 of a 30%
w/w NaOH-sohition was mixed into a dispersion contmaing 28 kg stabilised wheat
starch and 650 1 water. The mixture was stirred with a high shear mixex at 1500 rpm
for 10 minutes, allowng the starch to gdstimse. The starch in the earner fraction
corresponds with 3,25% of the total staidi content in the glue (1:30 ratio).
In a next stqj 550 I tap water was added to the carrisr together with 500 kg stabilised
wheat starch and 3 kg borax. The whale was mixed at 1500 rpm for an additional 5
Before addition of the rcmaitung alkali and starch, the remaining 12 I 30% w/w
NaOH solution was Srst diluted with 1001 of water.
Then 37 1 diluted alkali, followed by 200 kg of stabilised wheat staich was added
into the vessel. This mixture was stirred for 5 minutes before a second quantity of 37
1 of alkali and lis kg oi"starch, was euded. Agiin the is:--^jrc -v.'iz itirred ir-l-nEi'-e'v
Finally the remaining 381 alkali and 6,5 kg borax was added wtiile stirring the glue.
Tbt thu5 prepared glue formolaticm comprises iO% by weight starch solicis and is composed of;
NaOH : 6.25 g/1
In this example agJue is described containing 40% by weight maize starch solids. In
a 1500 I recipient. 24 tg maize stairij is dispersed in 440 1 watw. To this dispestion,
12 i^ of 33% wAv NaOH was aided and the mixture was stirred with a high shear
mixer for 12 minutes at 1500 rpm. The starch in the carrier fraction corresponds
vfbih 4^% of th« total starch content ro the glue (1:24 ratio).
In a next step 3201 water followed by 4,5 kg borax was added and intensively stin-ed
for 3 rmnutes- Then 300 kg starch were added to the carrier fraction and
homogeneously dispersed therem ay mixing ai i SCO rpiu fw on audiiioriaJ
3 minutes. Before addition of the remaining alkali and starch, this additional alkali
fraction (10 kg 33% NaOH) was diluted wkix 1001 of water.
Thus 37 I diluted alkali, followed by 151 kg of stabilised maize starch was added to the recipient, and stirred at 1500 rpm for 3 minutes. Then a second quantity of alkali, followed by 100 kg of starch was added and dispersed. Finally the remainiag 35 I alkali together with 4 kg of borax was added while stirring.
The thus prepared ghie fomiuiation compiisej 40% by weight starch solids and is oornposesd of.
Starch; 575 1^
NaOH: 6,25 g/J
Borax: 6,25 g/1
1. A method for preparing a Stein Hall adhesive, comprising the steps;
preparing a carrier portion by gelatinising at least a part of the total starch in the adhesive in an alkaline medium;
diluting the carrier portion with a volume of water; and
adding the remaining secondary starch;
wherein in a first step said carrier portion is prepared using part of the alkali, and in a second step the carrier portion is diluted with a volume of water, followed by the addition of at least a portion of the secondary starch, characterised in that a high dry substance Stein Hall adhesive, containing between 32 and 45 % dry weight starch solids, is prepared using a single mixing vessel, wherein in the first step said carrier portion is prepared in the single mixing vessel, and in a third step the remaining alkali is added in a diluted form together with the secondary starch.
2. The method as claimed in claim 1, wherein the addition of the remaining secondary starch and alkali is performed stepwise.
3. The method as claimed in claim 2, wherein the addition of alkali and starch is done in at least two steps.
4. The method as claimed in any one of the claims 1 to 3, wherein during the first step, a carrier portion is prepared containing between 2 and 9% of the total starch content by mixing the starch together with water and alkali until all the starch has gelatinised.
5. The method as claimed in any one of the claims 1 to 4, wherein in the first step, the alkali content in the carrier portion is typically less than 2/3 of the total amount needed in the adhesive formulation.
6. The method as claimed in any one of the claims 1 to 5. wherein the second step the carrier portion is diluted with a volume of water corresponding to 60 to 85% of the carrier volume.
7. The method as claimed in any one of the claims 1 to 6, wherein the second step 50 to 75% of the secondary starch is added.
8. The method as claimed in any one of the preceding claims, wherein after the third step borax is added.
9. High dry substance Stein Hall adhesive, obtained by a method as claimed in any one of the preceding claims, characterized in that it contains
between 32 to 45% native or stabilized starch;
the ratio carrier starch to secondary starch is between 1:50 and 1:11;
it shows a Bauer-viscosity between 21s and 60s; and
the alkali concentration in the glue is sufficient to provide a SGP of between 45°C and 53°C.
10. The high dry substance Stein Hal! adhesive as claimed in claim 9, wherein the native or stabilized starch is obtained from cereal, tuber or root starches.
|Indian Patent Application Number||1901/CHENP/2004|
|PG Journal Number||13/2009|
|Date of Filing||26-Aug-2004|
|Name of Patentee||TATE & LYLE EUROPE N V|
|Applicant Address||Burchtstraat 10, B-9300 Aalst,|
|PCT International Classification Number||C09J 103/02|
|PCT International Application Number||PCT/EP2002/000975|
|PCT International Filing date||2002-01-30|