FI68414B - STAERKELSEBASERAT LIM OCH FOERFARANDE FOER FRAMSTAELLNING AV DETTA - Google Patents

Description

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patent application Offenlegungsschrift

C Patent ayCnnetty 10 C9 1985

Patent ncddelat ^ (51) Kv.lk. * / Lnt.CI. * C 09 J 3/06 SUO Ml —FIN LAND (21) Patent application — Patentansökning 781045 (22) Application date - Ansökningsdag 05.04.78 / Fl) * '( 23) Starting date - Giltighetsdag 05.04.78 (41) Made public - Blivit offentlig 07.10.78

National Board of Patents and Registration Date of publication and publication. - R

Patent- and registerstyrelsen '1 Ansökan utlagd och utl.skriften publicerad 31. U5.05 (32) (33) (31) Privilege claimed — Begärd priority 06.04.77 England-England (GB) 14623/77 (71) CPC International, Inc., International Plaza, Englewood Cliffs,

New Jersey 07632, USA (72) Alan Arthur Procter, Swinton, Lancashire,

Ray Frederick Bryn Davies, Guildford, Surrey,

Brian Henry McErlean, Stretford, Manchester, England-England (GB) (74) Oy Kolster Ab (54) Starch-based adhesive and method for its production -

Stärkelsebaserat 1 im och förfarande för framställning av detta

The invention relates to a starch-based adhesive and a method for producing the same. In particular, the invention relates to a starch-based adhesive suitable for use in the manufacture of paperboard, such as corrugated board, which contains a small amount of gelatinized starch and a large amount of non-gelatinized starch.

Today, corrugated board is produced in a continuous work process comprising several steps. The slightly moistened paper web is passed through heated grooves. Glue is applied to the other side of the heated corrugated paper on the crest of each wave. Immediately thereafter, the corrugated paper is brought into contact with the surface paper web under heat and pressure to form a strong adhesive bond between the two layers. This product is known in the art as "unilaterally clad" corrugated board. Another type of corrugated board is a rigid grade of 2 68414, which is used, for example, in the manufacture of cardboard boxes. In forming this type of paperboard, additional glue is applied to the corrugated exposed corrugations during the addition step, and a second web of surface paper is brought into contact with the corrugated inner layer and glued to it under heat and pressure using a double coating machine.

The successful production of corrugated board with high speed machines (200 m or more per minute) which are normally used is very sensitive to the properties of the adhesive. Thus, in order to give a satisfactory product, the viscosity of the adhesive must be such that the adhesive flows easily in the apparatus while being recycled to keep it uniform. The adhesive must also be viscous enough to remain in place when applied by the wave brush and to fill any depressions inherent in the paper. In addition, due to the high speed of current machines, it must adhere to "blink gluing" when heat and pressure are applied to it.

Starch-based corrugated adhesives are traditionally formed within the Stein Hall process. This is a system in which the majority of the adhesive comprises unbroken unmodified corn starch granules slurried in water at a dry matter content of about 20%, the granules being kept in suspension by means of a carrier part which is cooked starch paste. The adhesive is in principle prepared by cooking the carrier part in an open container with fresh steam, usually in batches. However, recent developments have achieved continuous production of adhesive using a jet cooker under atmospheric pressure conditions to make a base section. This is then added to another container containing uncooked starch slurry (non-carrier portion). A typical Stein Hall adhesive has the following properties:

Gelling temperature 62-65 ° C; Stein Hall viscosity at 35 ° C - unilaterally coated, 30-35 seconds with double-sided 45-55 seconds; dry matter content -20% on a commercial basis (c / b) pH 11.8-12; the ratio of carrier starch to non-carrier starch is about 1: 5.5.

3 68414 Such adhesives suffer from various disadvantages: a) The amount of carrier (gelitinized) starch determines the initial stickiness of the adhesive, and this, together with the dry matter content of the adhesive, determines the speed at which the corrugating machine can be run.

It is difficult to produce a Sten Hall adhesive with an acceptable initial tack and dry matter content without also having an unacceptably high viscosity. Attempts to overcome this disadvantage have recently involved the use of chemically thinned starches, which give gelled solutions a lower viscosity but are substantially more expensive than unmodified starch and board adhesives must necessarily be fairly inexpensive products.

b) The viscosity stability of the adhesive is poor due to the tendency of the gelled starch to deteriorate or stick together when standing.

c) When the board product must be waterproof, it is common to include crosslinking resins in the adhesive. The heat used to gel the carrier moiety also affects the reaction between the starch and the crosslinking resin to obtain a water-resistant bond. However, the reactivity of conventional Stein Hall adhesives with crosslinking resins is poor.

It is an object of the present invention to overcome the above-mentioned disadvantages of conventional adhesives and to provide a continuous process by which improved adhesives can be prepared.

The invention relates to a starch-based aqueous adhesive having a solids content of 10-40%, preferably 10-35% by weight, a Stein Hall viscosity at 35 ° C of 20-100 seconds, preferably 25-55 seconds and comprising a weight ratio of 1: 2- 1: 8 a) a carrier part containing gelatinized starch, and b) a non-carrier part containing non-gelatinized starch having a gelling temperature of 55-75 ° C in the adhesive.

The adhesive is characterized in that the carrier part contains gelatinized, molecularly dispersed starch having a viscosity of up to 1000 cP, measured at a solids content of 10% and a temperature of 50 ° C.

4,68414

Unless otherwise stated, dry matter contents are expressed in this specification on a commercial basis (c / b), this means the ratio of commercially available starch to other dry matter in water. Commercially available starch contains a small proportion, typically about 12% water, so that an adhesive containing 20% c / b dry matter is equivalent to an adhesive containing 18% d / b (dry basis) dry matter.

Crude starch consists of molecular bundles held together by hydrogen bonds. Conventional gelation, e.g., by steam treatment at a temperature of up to 100 ° C, removes and partially, but not completely, breaks these bundles. In a molecularly dispersed starch such as that used in the carrier portion of the adhesives of this invention, the bundles are substantially completely dispersed and the individual starch molecules are substantially loose. Molecular dispersion of the starch is achieved by gelatinization under stringent conditions, such as using excess steam and temperatures above 100 ° C, as described more fully below. Molecularly dispersed starches are characterized in that their viscosity does not exceed 1000 centipoise, measured at a dry matter content of 10% and at a temperature of 50 ° C, typically of the order of 250 centipoise. The viscosity of conventionally gelled starch under these conditions is well over 1000 centipoise.

It is preferred to use unmodified starches to make the adhesives of this invention. Modified starches, such as etherified or esterified starches, may be used, but since they are normally more expensive than regular starch and little or no benefit is gained from their use, they are not considered preferred. Partially oxidized or acid or enzyme hydrolyzed starches can be used and this results in a lower viscosity upon gelatinization. But even if they are not molecularly dispersed, they do not have the required viscosity stability of 5,68414 and are not suitable for use in accordance with this invention. Although any cereal or vegetable starch can in principle be used in the adhesive and process of the present invention, corn or wheat starches for corrugated board adhesives are normally used.

Numerous water-dispersible high-viscosity polyhydroxy polymeric materials can be used to replace up to half of the starch used in the adhesive carrier. Examples are cellulose derivatives such as sodium carboxymethylcellulose, polyvinyl alcohols and hydrolyzed polyvinyl acetates, and polyvinylpyrrolidone.

As noted above, the solids content and the carrier / non-carrier ratio are relative to each other. In the preferred adhesives of this invention, the solids content and the base fraction / non-carrier weight ratio are in the range delimited graphically by linear curves depicting the dependence of the solids content on the carrier / non-carrier weight ratio, connected at the following four points:

Solids content

Weight ratio 1: 2 1: 2 1: 6 1: 8 This area is shown graphically in the attached figure 1.

Due to the lower viscosity of the molecularly dispersed carrier starch, the adhesive compositions of this invention have a lower carrier / non-carrier ratio (i.e., contain more carrier) than conventional Stein Hall adhesives at a given solids content and viscosity. This feature can be exploited in two ways. If the dry matter content is kept the same, then the adhesive has a better initial tack than Stein Hall adhesive. Under these conditions, the carrier / non-carrier ratio of the adhesive is preferably between 1: 2.5 and 1: 4.5, in particular between 1: 3 and 1: 4, and the dry matter content is between 15 and 25% by weight. Alternatively, the dry matter content can be increased without a large loss of initial tack to obtain a drier adhesive and thus make the corrugator work faster than when using Stein Hall adhesive. Under these conditions, the carrier / non-carrier ratio of the adhesive may preferably be between 1: 4-1: 6 and the dry matter content between 20-30% by weight.

The gelation temperature of the non-carrier part of the starch in the adhesive is preferably between 60 and 70 ° C, in particular between 63 and 66 ° C. If this temperature is too low, premature geling of the starch and thickening of the adhesive can occur. If the temperature is too high, an unreasonable amount of heat is needed to make the adhesive fully effective. The gelation temperature is primarily determined by the proportion of sodium hydroxide in the adhesive. Sodium hydroxide is generally used in an amount of up to 5% by weight, preferably 2-3.5% by weight, based on the weight of the starch.

Borax is also commonly used in Sten Hall adhesives to stabilize viscosity and increase tack. It is recommended to use up to 5% by weight, preferably 0.75-3.25% by weight of borax in the weight of the starch in these adhesives. When a waterproof joint is required, crosslinking agents or preformed resins can be added to the adhesive according to conventional practice. In accordance with standard practice, other additives may be further included.

The invention also relates to a process for preparing the starch-based aqueous adhesive described above. The process is characterized in that a) a carrier part containing gelatinized molecularly dispersed starch with a solids content of 3-40% by weight is prepared by cooking a starch slurry using a jet cooker at a temperature of 110-170 ° C and a steam amount of is at least 1.1 times greater than that required to heat the slurry to the required temperature, b) the carrier part is mixed with a non-gelatinized starch slurry having a solids content of 10-40% by weight, 7 68414 in such a ratio that the total solids content becomes 10-40% by weight - and the weight ratio of gelatinized starch to non-gelatinized starch becomes 1: 2 to 1: 8, and c) not more than 5% by weight of alkali, based on the amount of starch, is added to the resulting mixture so that the gelatinized temperature of non-gelatinized starch is 55-75 ° C.

An important aspect of the method of the present invention is the use of a jet cooker with an excess of steam under overpressure to cook the starch carrier portion. Such cooking is not new, it is described, for example, in U.S. Patent 3,133,836, but it has not previously been used in the manufacture of the carrier part for starch-based adhesives. The jet cooker operates under very high shear conditions and these are made even more severe by using pressures higher than atmospheric pressure, cooking temperatures between 110-170 ° C, preferably between 130-155 ° C, and excess steam. If the cooking temperature is predetermined, the amount of steam which is just sufficient to heat the starch slurry to this temperature and which completely condenses in doing so can be easily calculated. According to the invention, an excess of steam is used compared to what is needed to heat the slurry, the excess passing through the digester without condensing. The amount of steam should be at least 1.1 times the amount of steam required to heat the slurry to the cooking temperature, preferably 1.25-5, especially 1.5-3 times the amount required. The use of these stringent conditions results in a more complete disintegration of the starch granules than is common in gelling processes. The starch subjected to this treatment is in a molecularly dispersed state. The viscosity of the starch paste obtained (at a certain dry matter content) depends on the cooking time and temperature and the excess steam used, but is always substantially lower than the viscosity of the starch solution obtained to gel under normal conditions. In particular, the viscosity of the starch gelled in the jet digester using a temperature of at least 110 ° C and at least 1.1 times the amount of steam required (measured at 10% solids and 50 ° C) is not greater than 1000 centipoise, preferably 100-500 centipoise, especially 150-200 centipoise. In contrast, the viscosity of a normally gelled starch solution under the same conditions would be 6-70 ° C centipoise.

The final adhesives have a dry matter content of 10-40% by weight c / b, preferably 15-30 c / b, e.g. 20% c / b, and are selected in view of the viscosity, the initial adhesive strength and the final adhesive strength of the adhesive. with the desired dry matter content (e.g. 20% c / b) can be obtained by mixing the appropriate parts with a carrier part containing 20% dry matter c / b and a non-carrier part containing 20% dry matter c / b, or by mixing a dilute carrier part. part with a more concentrated non-carrier part, or by mixing the more concentrated carrier part with a more dilute non-carrier part.

The dry matter content of the carrier part can be 3-40%, preferably 5-35% and in particular 10-20% by weight c / b. Above a dry matter content of 20%, the gelled starch solution tends to gel when standing, which is a disadvantage, although not an unsolved problem. When using a jet sprayer with a dry matter content of less than 10%, there have been some difficulties in obtaining the required temperature in the final adhesive mixture. As for the non-carrier part of the starch, slurries containing 10-40% by weight of c / b dry matter can be easily treated. The dry matter content of the non-carrier slurry should be selected in proportion to the dry matter content of the carrier solution and the amounts that the two are mixed together to obtain the final adhesive combination having the desired dry matter content.

Non-carrier starch slurry is normally used at an ambient temperature of 9,68414. However, the carrier part has just passed through the jet cooker at a high temperature.

If the carrier portion and the non-carrier portion are simply mixed together, it is likely that a non-carrier starch will prematurely occur. Therefore, normal practice is to ensure that the temperature of the mixture does not rise above 4 ° C. To achieve this, the carrier part of the starch should normally be cooled; the temperature to which it must be cooled depends on the relative volumes of the two parts and can be easily calculated in each particular case.

The carrier and non-carrier moieties are mixed together in such amounts as to provide an adhesive combination having the desired viscosity. Since the viscosity of the carrier used is substantially lower than the viscosity of the gelled starches previously used as carriers, the carrier / non-carrier ratio for a standard dry matter content of about 20% by weight c / b is necessarily lower than the conventional 1: 5.5 by weight, and it has in fact been found to be in the range of 1: 2.5 to 1: 4.5, in particular 1: 3.0 to 1: 4.0 by weight. At ratios greater than 1: 4.0, it has been found that the viscosity of the adhesive combination is quite too low for suitability. At ratios of less than 1: 3.0, these adhesive compounds have an unreasonably high viscosity that could be reduced to an acceptable level only by excessive dilution with water. An adhesive combination containing 20% c / b dry matter with a carrier / non-carrier weight ratio of 1: 3.5 has a suitable viscosity, or can be easily diluted with a small amount of water to give the desired viscosity. The use of different cooking conditions or different solids content could be expected to give a different preferred carrier / non-carrier ratio. The preferred Stein Hall viscosity of the adhesives of this invention at 35 ° C is 25-55 seconds, preferably 6841 4 10 28-38 seconds for adhesive compounds for single sided coating and 45-55 seconds for dual surface combinations.

As stated above, the adhesives of this invention preferably contain sodium hydroxide to lower the gelation temperature of the non-carrier starch. This sodium hydroxide is most conveniently combined with the starch carrier and can be incorporated into the crude starch slurry, which is transported to a jet cooker. Alternatively, sodium hydroxide may be combined with the non-carrier portion or a mixture of the carrier portion and the non-carrier portion. Preferably, the sodium hydroxide is partitioned between the carrier and non-carrier feed slurries.

As stated above, the adhesives of this invention preferably contain borax. Borax can be conveniently incorporated into the non-carrier portion of starch. Alternatively, it may be added during the final mixing of the carrier part and the non-carrier part. Adding all of the borax to the starch slurry transported to the pressurized jet cooker can cause viscosity problems.

It may be advantageous to prepare a simple crude starch slurry, optionally containing some or all of the sodium hydroxide and borax desired in the final adhesive combination, and divide this slurry into two streams, one of which is passed through a jet cooker to gel the starch, and then recombined at this point. any additional sodium hydroxide or borax required.

The adhesive and method of the invention offer the following advantages over the conventional Stein Hall adhesive and its manufacturing process: 1) A higher carrier / non-carrier ratio is possible without the need to resort to expensive, low viscosity, modified starches. Carrier / non-carrier ratios of 1: 2.5 to 1: 4.5 can be achieved without the usual increase in viscosity associated with unmodified carrier starch which has been subjected to gelation by conventional methods.

2) The adhesive has a higher initial adhesive strength, which is helpful during early bond formation.

3) Alternatively, a higher dry matter content is possible with the same carrier / non-carrier ratio without resulting in an impossibly high viscosity, which allows the corrugating machines to be driven faster.

4) The carrier part, which is completely monomolecularly dispersed, has a higher viscosity stability than conventionally prepared starch and the final adhesive is less sensitive to shear forces.

5) The final mixture has a higher tack due to the way the carrier is dispersed and the higher proportion of carrier present.

6) A higher carrier ratio gives an adhesive that reacts better with crosslinking resins to obtain a waterproof bond.

7) The method allows the production of corrugated adhesive on a continuous basis.

The following examples illustrate the invention. In Examples 1 and 2, two separate aqueous cornstarch slurries are prepared to act as a carrier and the other as a non-carrier. Sodium hydroxide is partitioned between carrier and non-carrier slurries; all borax is added to the non-carrier slurry. The carrier slurry is boiled under overpressure in a jet cooker under the following conditions: Vapor pressure 5.8-6.5 atm

Cooking temperature 152-155 ° C

Back pressure 5.8-6.2 atm

Carrier flow rate 7.6 1 / min

The viscosity of the obtained carrier part (measured at a dry matter content of 10% by weight and at 50 ° C) was between 150 and 68 centipoise, and the carrier part was mixed with the non-carrier part to give the desired adhesive combination.

Example 1 In this experiment, the dry matter content of the adhesive combination was kept constant at 20% by weight c / b, and the effect of the variation in the ratio (carrier / non-carrier) on the viscosity of the obtained adhesive was determined. The results are shown in Table 1 below. The temperatures of the carrier and non-carrier part and the final adhesive are also shown in this table; it should be noted that in three cases the temperature of the final adhesive was higher than 40 ° C; this does not appear to be detrimental to the small scale conditions used in this experiment, but would be undesirable in a commercial process. The viscosity of the adhesive at the carrier / non-carrier ratio of 1: 3 was quite high, but this could have been reduced either by changing the cooking conditions of the carrier or by diluting the final adhesive.

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Example 2 In this experiment, the dry matter content of the adhesive was kept at 20% c / b and the carrier / non-carrier ratio was kept at 1: 3.5. The effect of variation in the sodium hydroxide and borax contents of the adhesive was determined and the results are shown in Table 2 below. In this table, adhesives containing 3.75% and 5% borax were not useful. Adhesives containing 1.5%, 1.0%, and 0.5% sodium hydroxide had a fairly high viscosity, which, however, could have been improved by dilution.

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Example 3 Reference is made here to Figure 2 of the accompanying drawings, which is a schematic representation of a factory for carrying out the method of the present invention. The percentage of sodium hydroxide and boo-5 raks is calculated from the weight of c / b of starch.

Referring to Figure 2, the number 10 denotes a slurry tank to which: water is supplied via line 12; sodium hydroxide via line 14; borax through line 16; and granular corn starch via line 18. The slurry tank 10 contains 20% by weight of c / b dry matter, 2.5% by weight of sodium hydroxide and 0.1% by weight of borax. The slurry is continuously removed from the bottom of the tank 10 via line 20 and is divided into two separate streams, 22% to line 22 and 78% to line 24 (i.e., the ratio is 1: 3.5). The slurry in line 22 passes 15 to a jet cooker 26, commercially available under the trademark Nemo Junior, where it is boiled as in Examples 1 and 2 with excess steam obtained via line 28 and then passed to tank 30. Slurry stream in line 24 is transported to another holding tank 32, 20 wherein an additional 3% by weight of borax from derivative 33 is added (to give 2.5% by weight of the final combination).

The carrier portion of the combination from the container 30 and the non-carrier portion from the container 32 are conveyed to the in-line mixer 34 where they are thoroughly mixed and then to the storage tank 36. It may be advantageous to return part of the adhesive combination from the storage tank 36 via line 38 to a mixer 34. The resulting adhesive combination has a Sten Hall viscosity at 35 ° C of 41-45 se-30 municipalities. It is removed, as appropriate, via line 40 for use with a dual coating machine, or via line 42 for dilution prior to use with a single-sided vending machine, if available.

The properties 17 6841 4 of the adhesives prepared in the experimental factory experiments using the equipment described above are shown in Table 3, which also gives the properties of a conventional Sten Hall adhesive for comparison. It is found that the reproducibility is quite good and that the properties correspond to those of a conventional Sten Hall adhesive. It should be noted that Table 3 is designed to show that corrugated board adhesive with commercially acceptable properties can be made on a continuous basis; the table is not intended to show the superiority of these adhesive combinations over ordinary adhesives.

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Examples 4 and 5 are comparative examples intended to show the difference in the carrier / non-carrier ratio required to prepare adhesives at two different dry matter contents using the method of the present invention and the conventional Stein Hall method.

Example 4 20% dry matter content 1. Standard Stein Hall method 18 g of corn starch were slurried in 80 g of water and heated to 70 ° C. To this slurry was added 3.2 g of sodium hydroxide dissolved in 8 g of water. The mixture was stirred and kept at 70 ° C for 15 minutes, after which time 100 g of cold water was added.

This cooked starch paste (carrier) was added to a slurry containing 88 g of corn starch, 260 g of water and 3.2 g of powdered borax and mixed for 15 minutes.

Glue properties:

Sten Hall viscosity = 48 s at 20 ° C Dry matter content = 20.1% on a commercial basis

Carrier starch / non-carrier starch ratio = 1: 4.9 2. Method of the invention

A slurry containing 83.5 parts of water, 13.2 parts of corn starch and 3.3 parts of 10% sodium hydroxide was treated in a jet heater at 150 ° C using 5.5 atmospheric vapor pressure. The solids content of the resulting starch paste was 11% on a commercial basis after steam condensation.

180 g of this carrier paste was added to a slurry containing 230 g of water, 70 g of corn starch, 1.7 g of sodium hydroxide and 2.2 g of finely divided borax powder, and mixed for 10 minutes.

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Glue properties:

Sten Hall viscosity = 47 s at 20 ° C

Dry matter content = 19.4% on a commercial basis

Carrier starch / non-carrier starch ratio = 1: 3.5

Example 5 25% dry matter content 1. Standard Stein Hall method 18 g of corn starch were slurried in 80 g of water and heated to 70 ° C. To this slurry was added 3.9 g of sodium hydroxide dissolved in 10 g of water. The mixture was stirred and kept at 70 ° C for 15 minutes, after which time 100 g of cold water was added.

This cooked starch paste (carrier) was added to a slurry containing 112 g of corn starch, 220 g of water and 3.9 fine borax powder and mixed for 15 minutes.

Glue properties:

Sten Hall viscosity = 50 s at 20 ° C Dry matter content = 25.2% on a commercial basis

Carrier starch / non-carrier starch ratio = 1: 6.2 2. Method of the invention

A slurry containing 83.5 parts of water, 13.2 parts of corn starch and 3.3 parts of 10% sodium hydroxide was treated in a jet heater at 150 ° C using 5.5 atmospheric vapor pressure. The resulting starch paste had a dry matter content of 11% on a commercial basis after steam condensation.

180 g of this carrier paste was added to a slurry containing 210 g of water, 100 g of corn starch, 2.5 g of sodium hydroxide and 3.0 g of finely divided borax powder and mixed for 10 minutes.

Glue properties:

Stein Hall viscosity = 52 s at 20 ° C Dry matter content = 25.3% on a commercial basis

Strain / starch / non-carrier starch ratio = 1: 5.1.

Claims (11)

1. Starch-based, aqueous adhesive, on a starch basis, the solids content of which is 10-40% by weight and Stein Hall viscosity at 35 ° C is 20-100 seconds and comprises in the weight ratio of 1: 2-1: 8 a) a carrier portion containing gelatinized starch and b) a non-carrier portion containing ungelatinized starch whose gelatinization temperature in the adhesive is 55-75 ° C, characterized in that the carrier portion contains gelatinous, molecularly dispersed starch, whose viscosity is not more than 1000 cP measured at a solids content of 10% and a temperature of 50 ° C. 2. Adhesive according to claim 1, characterized in that the solids content and the carrier / non-carrier weight ratio are within an area graphically constrained by linear curves which describe the dependency of the solid substance on the carrier / non-carrier weight ratio and which bonded in the following four points: solids content 10 20 35 35 weight ratio 1: 2 1: 2 1: 6 1: 8 3. Adhesive according to claim 1 or 2, characterized in that the solids content is 15-25% by weight. 4. Adhesive according to any one of claims 1-3, characterized in that the weight ratio of the carrier portion to the non-carrier portion is 1: 2.5-1: 4.5. 5. Adhesive according to any of claims 1-4, characterized in that the carrier portion contains gelatinous, molecularly dispersed unmodified maize or wheat starch. 6. Adhesive according to any one of claims 1-5, characterized in that the viscosity of the starch molecularly dispersed is 100-500 cP (measured at a solids content of 10% and a temperature of 50 ° C). . 7. Adhesive according to any one of claims 1-6, characterized in that the non-carrier portion is ungelatinised, unmodified maize or wheat starch, whose gelatinization temperature in the period of time is from 6 to 66 ° C. 8. Adhesives according to any one of claims 1-7, characterized in that at present there are also 2-3.5% by weight sodium hydroxide and 0.75-3.25% by weight borax calculated on the amount of starch. 9. A process for preparing a starch-based aqueous adhesive according to any one of claims 1-8, characterized in that: a) preparing a carrier portion containing gelatinous, molecularly dispersed starch having a solids content of 3-40% by weight by boiling a starch slurry using a syringe boiler, where the temperature is 110-170 ° C, and a meadow amount of at least 1.1 times greater than that needed to heat the slurry to the required temperature; b) mixing the carrier portion having a slurry of ungelatinized starch having a solids content of 10-40% by weight in such a ratio that the total solids content will be 10-40% by weight and the weight ratio of the gelatinized starch to the unelatinized starch is 1: 2-1: 8, and c) add a maximum of 5% by weight of alkali, calculated on the amount of starch, to the mentioned mixture, such that the gelatinizing starch temperature of the gelatin is 55-75 ° C. Method according to claim 9, characterized in that in step a) a syringe boiler is used, where the temperature is 130-155 ° C, and a meadow quantity 1.5-3 times greater than that needed to heat the slurry. to the required temperature. The method of claim 9 or 10,