GB1559667A

GB1559667A - Method of manufacturing a predominantly starch containing paper bag adhesive

Info

Publication number: GB1559667A
Application number: GB13707/78A
Authority: GB
Original assignee: Vehna Oy AB
Current assignee: Vehna Oy AB
Priority date: 1977-08-03
Filing date: 1978-04-07
Publication date: 1980-01-23
Also published as: FI772355A; DE2820320C2; FR2399471A1; NO150125B; FI61319C; SE7804484L; SE442405B; DE2820320A1; FR2399471B1; NO782649L; ATA357878A; AT358691B; FI61319B; NO150125C

Description

(54) METHOD OF MANUFACTURING A PREDOMINANTLY STARCH CONTAINING PAPER BAG ADHESIVE (71) We, OY VEHNA AB, a joint stock company organised under the laws of Finland, of SF-21200 Raisio, Finland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention concerns a method of manufacturing a paper bag adhesive containing predominantly starch, the method being characterized by the fact that starch is brought into a substantially water soluble form by mixing an aqueous slurry of starch or a predominantly starch containing composition at a temperature of 120 to 200"C at super atmospheric pressure.

As paper bags are mass produced articles the use of which for packing purposes at least to some degree is due their low cost, relatively expensive synthetic glues such as plastic glues are not generally used for their manufacture.

On the other hand, several adhesives manufactured from starch are prior known which are suitable for gluing paper bags. A detailed description of starch containing paper bag adhesives is found i.a. in a publication by Rudolf Köhler entitled "Stärkeklebstoffe", Verlag Paul Parey, Berlin 1971, p. 54, 75 to 81 and 93 to 94 and in the publication edited by J. A. Radley "Industrial Uses of Starch and Its Derivatives", Applied Science Publishers Ltd., London, 1976, pps. 11 onwards.

Alkaline borated dextrin glues were earlier used almost exclusively for the manufacture of paper bags. The dextrins are prepared by heating starch on a hot base plate to temperatures of about 180 to 200"C or by mixing into the starch small amounts of an acid and heating the mixture obtained to temperatures of about 130 to 150C. As a result of this mode of manufacture the polymeric glucose chains of the starch break down and generally somewhat coloured products soluble in cold water are obtained. The dextrins always contain some liberated glucose. The dextrin adhesives are delivered to the customers either as powders which the customer dissolves in water to form concentrated solutions containing even up to 60 to 70% by weight of dry matter, or as solutions ready for use.The properties of the adhesive are usually improved by adding 2 to 5% by weight of borax and 0.5 to 1% by weight of sodium hydroxide and the final adhesive is thus generally alkaline the pH being usually about 9 to 10.

Later use was being made of starch adhesives in which the splitting of the starch polymeric chains is substantially less than in dextrins and which thus are distinctly less soluble in water. Thus adhesives manufactured from so called acid starches are known. These modified starches are prepared by forming a slurry of the starch in water, adding a suitable acid and heating the slurry obtained to a temperature at the most 80"C. The products obtained are generally soluble only in hot water and they are used for gluing paper bags as solutions containing normally 10 to 25% by weight of dry matter. The use of oxidized starches as paper bag adhesives is also known.

These modified starches are prepared by forming a slurry of the starch in water and treating the same with oxidizing agents such as hydrogen peroxide, sodium peroxide, potassium persulphate, barium peroxide or sodium hypochlorite, the pH usually being over 7 and at temperatures which are less than the gelatinization temperature of the starch used, that is generally less than 600C. The water solubility of the oxidized starches depends on the amount of oxidizer, the treatment time and the temperature. Some products may be dissolved even into cold water, although only to fairly diluted solutions, some dissolve only upon boiling in water. The concentration for application of the adhesive is generally 15 to 20%.

It is also known to use chemically further modified starches for gluing paper bags. They are usually more expensive than the simpler starch adhesives, but they have generally better gluing characteristics. Modified starches of this kind are starch esters and ethers. Of the former starch phosphates and acetates and of the latter oxyethyl starches may be mentioned.

It is also known to use combinations of modified starches, for example a mixture of an add starch and a starch ether together with certain additives as proposed e.g. in U.S.

patent 3,844,807 (1974). Finally it is known to use several different kinds of additives besides the starch in paper bag adhesives. Of these polymeric resins and dispersions improv ing the water resistance of the adhesive seam may be mentioned such as urea-formaldehyde resin and polyvinylacetate dispersion.

A common problem connected with the use of starch adhesives is obtaining a suffidently fast initial tack of the glued sur faces, especially in fast bag manufacturing machines in which a prolonged detention time is not used between the gluing of the longi tudinal seam and that of the bottom seam.

Those skilled in the art often use for gluing the bottom seam a different adhesive than in the longitudinal seam. Also the strength of the glued seam often exhibits drawbacks.

One difficulty is related to the viscosity of the adhesive which easily can become too high.

It is true that it in this case is possible to dilute with water but simultaneously the amount of water to be evaporated from the glued seam is larger. A method of modifying unsuitable for the starch in question as well as too high or too low an adhesive viscosity easily causes splattering of the adhesive in the bag manufacturing machine. Also the stability of the viscosity of the adhesive during mechanical stress as well as during possible storage leaves much to be desired. Finally it may be concluded that most starch adhesives have a too "long" structure which in the art means that the adhesive strand may be stretched to a very high degree without the strand breaking.Apparently a great part of the above listed difficulties are due to the fact that in known starch containing paper bag adhesives, with the exception of dextrin adhesives, the crosslinks between the polymer chains characteristic to the polymer structure of the starch still exist to a substantial degree also after the reactions taking place during the preparation of the modified starches. This is also supported by the detrimental retrogradation of the gently hydrolyzed or modified starches used as bag adhesives, which retrogradation takes place when the adhesives cool for example during storage. The term has been given to denote a partial separation of the starch dissolved in hot water as an insoluble precipitation when the solution cools. The separation is irreversible and is due to the crystallization and agglomeration of the straight chained amylose contained in the starch.

The method according to the invention aims at obtaining an adhesive prepared predominantly from starch and suitable for gluing paper bags also on high speed bag manufacturing machines, the adhesive having good initial tack properties and giving a strong glued seam, a paper bag adhesive which equally well may be used for gluing all the seams in the bag and the viscosity of which may easily be kept within a viscosity range suitable for the bag manufacturing machine and which in practice remains unchanged during prolonged mechanical handling and/or storage of the adhesive, and which does not splatter in the bag manufacturing machine, a paper bag adhesive having a minimal tendency for retrogradation, a paper bag adhesive which may be manufactured in the paper bag factory in a simple manner from ordinary unmodified starch or from a predominantly unmodified starch containing composition of matter.

According to the present invention a method of manufacturing a starch-containing paper bag adhesive comprises bringing the starch into a substantially water soluble form by mixing the starch or a starch-containing aqueous slurry having 5 % to 30% by weight starch, at a temperature of 1200C to 200"C at super atmospheric pressure whereby the viscosity of the final adhesive is 700 to 5000 mPas 'cup) measured at 25"C with a Brookfield viscosimeter using spindle No. 4 and a speed of 20 r/min.

It has been discovered that when starch or starch dissolved in water to form a slurry containing 5 to 30% by weight of starch is mixed in a closed vessel at temperatures of 120 to 200"C at super atmospheric pressure, which depending on the temperature may be 0.3 to 1.0 MPa, the starch granules break and both polymer components of the starch, the straight chained amylose and the branched amylopectin, separate from each other. Depending on the treatment time and the temperature the glucose polymer chains of the starch may separate completely when the crosslinks between the chains disappear. Thus a series of aqueous starch solutions is obtained characterized by a low viscosity and a substantially reduced tendency for retrogradation. Furthermore, they exhibit a "short'7 structure which manifests itself as a breaking of the adhesive strand upon gentle stretching thereof. When for example an aqueous slurry containing 15% by weight of starch is vigorously mixed at 1600C at a pressure of 0.7 MPa for a few seconds, a starch solution is obtained the viscosity of which at 90"C is 700 to 1000 mPas (cp) and at 25"C 2000 to 3000 mPas (cp) measured with a Brookfield viscosimeter using spindle 4 and a speed of 20 revolutions per minute (20 r/min).

It has now been discovered that the starch slurries prepared by the above mentioned thermomechanical treatment may successfully be used either as such or together with certain additives for gluing paper bags in modern high-speed paper bag machines. It has also been discovered that the same adhesive may be used for gluing both the longitudinal as well as the transverse and the bottom seam in the bags.The viscosity of the adhesive remains within an applicable viscosity range also during prolonged mechanical strain, such as mixing, pumping, during circulation in piping and pressure on adhesive rolls, neither does the storage of the adhesive cause detrimental changes therein, It is not possible for the time being to give a definite explanation as to the good initial tack and the strong adhesive bond obtained with the paper bag adhesive according to the invention, but it is believed that when water evaporates from the glued seam the polymer chains once again move close to each other and are simultaneously aligned so that the cross links between the polymer chains are reconstituted. To the adhesive may be added, either before the thermomechanical treatment or after the same, generally used additives.Such are the inorganic bases such as sodium hydroxide, which added before the thermomechanical treatment lower the gelatinization temperature of the adhesive and thus allow the use of lower temperatures in the thermomechanical treatment, and which added to the finished adhesive coarsen the surface to be glued and thus promote the penetration of the adhesive into the surface. Further borax may be used to promote the formation of bonds between the polymer chains of the starch and carboxy methyl cellulose or corresponding, either synthetic or natural gelatinization agents to increase the viscosity of the adhesive. Into the adhesive according to the invention may be further added synthetic resins improving the water resistance of the glued seam such as an urea-formaldehyde-resin or synthetic polymer dispersions, such as polyvinyl acetate.

Into the adhesive may also be added, either before the thermomechanical treatment or after the same, mineral fillers such as kaolin, talcum or calcium carbonate, the purpose of which is to increase the dry matter content of the adhesive and thus to reduce the amount of water to be driven off from the glued seam, and on the other hand, when added before the thermomechanical treatment, by penetrating between the starch grains in the aqueous slurry to separate the grains from each other and thus to promote the simultaneous and equally effective thermomechanical treatment of each individual grain of starch. In addition, the mineral fillers in the finished adhesive can control the penetration of adhesive into the surfaces to be glued thus preventing the adhesive from being absorbed too fast.Mineral fillers, advantageously kaolin, is suitably used at an amount of 5 to 30% by weight of dry matter of the adhesive.

The thermomechanical treatment of the starch or predominantly starch containing composition of matter and the use of additives and fillers is according to the invention modified so that viscosity of the final adhesive ready to be used is within the viscosity range 700 to 5000 mPas (cP), advantageously 1000 . . . 3000 mPas (cP) measured at 25"C with a Brookfield viscosimeter, spindle 4 and speed 20 r/min. This requirement-restricts i.a. the applicable amounts of additives affecting the viscosity; thus sodium hydroxide maybe used in the range 0.1 % to 2% by weight of dry matter of the adhesive, borax 0.1% to 10% by weight and carboxy methylcellulose also 0.1% to 10% by weight Mineral fillers such as kaolin affect only little the viscosity of the adhesive.

The aqueous slurry of the thermomechanically treated starch or predominantly starch containing composition of matter may also be dried in a manner known per se to a dry matter content so that the powder obtained, which is easy to pack and transport, is resistant to microbiological degradation. The invention thus concerns also dried paper bag adhesives containing starch or predominantly starch and being thermomechanically treated in above mentioned manner.

The above mentioned thermomechanical treatment may be applied to any starch or starch derivative, whereby as raw material ordinary raw starches, such as wheat, corn, potato and rice starches or modified starches such as oxidized starches, starch esters and ethers may be used. As the adhesive component containing predominantly starch also thermomechanically treated types of flour may be used, wherein the amount of starch of the dry matter of the flour is more than 60% by weight, or a starch fraction obtained from the wheat starch manufacture containing besides starch 1 to 8% by weight of pentosans and 1 to 10% by weight of proteins of the dry matter of the fraction.The most advantageous raw materials for the paper bag adhesive according to the invention are the ordinary unmodified starches and the above mentioned starch fraction containing pentosans and proteins.

The invention is further illustrated bv the following examples concerning some modes of application of the invention, but they do not limit the scope of the invention.

Example 1 15 kg of potato starch was suspended in 85 1 of water and the slurry was heated while stirring at 160 C at a pressure of 0.7 MPa for three seconds with direct steam. The dry matter content of the adhesive slurry obtained was 14% by weight and the viscosity about 2000mPas (cP) measured at 25"C with a Brookfield viscosimeter using spindle nr. 4 and a speed of 20 r/min. The adhesive tests were performed on a paper bag paper using a glued seam having a thickness of 60 ,,am and a width of 50 mm. The strength of the glued seam was determined by measuring the force needed to separate the glued surfaces from each other by means of an Alwetron-device known in the art using a pulling speed of 100 mm/min.The following test results were obtained: Drying time (min) 5 10 30 1000 Releasing force (N/m) 100 110 250 350 Example 2 15 kg of wheat starch and 2.5 kg of kaolin were suspended in 85 1 of water and the slurry was treated with direct steam according to Example 1. The dry matter content of the adhesive slurry obtained was about 16% by weight and the viscosity about 2200 mPas (cP) measured at 25"C. When measuring the strength of the glued seam with the Alwetrondevice the following results were obtained: Drying time (min) 5 10 30 1000 Releasing force (N/m) 120 140 295 380 The viscosity of the adhesive was measured on different adhesive rolls in a paper bag manufacturing machine whereby the adhesive was put under mechanical strain of varying magnitude.The following results were obtained: Dry matter of adhesive Viscosity of adhesive (% by weight) (mPas) 14 to 15 1500 to 1700 15 to 16 1700 to 1900 16 to 17 1900 to 2200 17 to 18 2200 to 2600 mPas (cP) Initial adhesive 2200 Gluing of the transverse seam 1900 Gluing of the longitudinal seam 1700 Gluing of the bottom seam 1500 The reduction of the viscosity under mechanical stress is a general feature of starch adhesives, but a test run on the paper bag machine showed that the viscosity remained excellently within the desired viscosity range.

By varying the dry matter content of the adhesive according to Examples 14 to 18 ó by weight and the process temperature 22 to 32"C it could be observed that the viscosity of the adhesive still remained well within the desired viscosity range: Example 3 15 kg of corn starch was suspended in 80 1 of water and into the slurry was mixed 0.15 kg of sodium hydroxide as a 15% by weight aqueous solution. The slurry was treated with direct steam according to Example 1 at a temperature of 130"C. The dry matter content of the adhesive slurry obtained was 14% by weight and the viscosity 2000 to 2200 mPas (cP) measured at 25"C. Into the adhesive slurry was added 10% by weight, calculated from the total amount of adhesive, of an ordinary polyvinylacetate dispersion.The glue tests were performed as in Example 1 by using bitumen treated paper as the surfaces to be glued. For the strength of the glued seam according to Alwetron - measurements the following results were obtained: Drying time (min) 10 30 1000 Releasing force (N/m) 40 100 320 When using polyethene covered paper in the glue tests the following strength values were obtained for the same adhesive: Drying time (h) 24 46 1 week Releasing force (N/m) 60 150 500 Example 4 15 kg of wheat starch and 2.5 kg of kaolin were suspended in 85 1 of water and the slurry obtained was treated according to Example 1 with direct steam at a temperature of 145 C The viscosity of the adhesive slurry obtained was 3500 to 4000 mPas (cP) measured at 25"C.

Example 5 13 kg of wheat starch fraction which besides starch contained 3.4% by weight of pentosanes and 4.3% by weight of proteins, were suspended in 85 1 of water and treated according to Example 1 with direct steam at 1600C.

Thereafter 2.5 kg of kaolin was mixed into the slurry. The viscosity of the adhesive was 1000 to 1500 mPas (cP) measured at 25"C.

WHAT WE CLAIM IS: 1. A method of manufacturing a starch

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Claims

**WARNING** start of CLMS field may overlap end of DESC **.

glued seam having a thickness of 60 ,,am and a width of 50 mm. The strength of the glued seam was determined by measuring the force needed to separate the glued surfaces from each other by means of an Alwetron-device known in the art using a pulling speed of 100 mm/min. The following test results were obtained: Drying time (min) 5 10 30 1000 Releasing force (N/m) 100 110 250 350 Example 2

15 kg of wheat starch and 2.5 kg of kaolin were suspended in 85 1 of water and the slurry was treated with direct steam according to Example 1.The dry matter content of the adhesive slurry obtained was about 16% by weight and the viscosity about 2200 mPas (cP) measured at 25"C. When measuring the strength of the glued seam with the Alwetrondevice the following results were obtained: Drying time (min) 5 10 30 1000 Releasing force (N/m) 120 140 295 380 The viscosity of the adhesive was measured on different adhesive rolls in a paper bag manufacturing machine whereby the adhesive was put under mechanical strain of varying magnitude.The following results were obtained: Dry matter of adhesive Viscosity of adhesive (% by weight) (mPas)

14 to 15 1500 to 1700

15 to 16 1700 to 1900

16 to 17 1900 to 2200

17 to 18 2200 to 2600 mPas (cP) Initial adhesive 2200 Gluing of the transverse seam 1900 Gluing of the longitudinal seam 1700 Gluing of the bottom seam 1500 The reduction of the viscosity under mechanical stress is a general feature of starch adhesives, but a test run on the paper bag machine showed that the viscosity remained excellently within the desired viscosity range.

By varying the dry matter content of the adhesive according to Examples 14 to 18 ó by weight and the process temperature 22 to 32"C it could be observed that the viscosity of the adhesive still remained well within the desired viscosity range: Example 3

15 kg of corn starch was suspended in 80 1 of water and into the slurry was mixed 0.15 kg of sodium hydroxide as a 15% by weight aqueous solution. The slurry was treated with direct steam according to Example 1 at a temperature of 130"C. The dry matter content of the adhesive slurry obtained was 14% by weight and the viscosity 2000 to 2200 mPas (cP) measured at 25"C. Into the adhesive slurry was added 10% by weight, calculated from the total amount of adhesive, of an ordinary polyvinylacetate dispersion.The glue tests were performed as in Example 1 by using bitumen treated paper as the surfaces to be glued. For the strength of the glued seam according to Alwetron - measurements the following results were obtained: Drying time (min) 10 30 1000 Releasing force (N/m) 40 100 320 When using polyethene covered paper in the glue tests the following strength values were obtained for the same adhesive: Drying time (h) 24 46 1 week Releasing force (N/m) 60 150 500 Example 4

15 kg of wheat starch and 2.5 kg of kaolin were suspended in 85 1 of water and the slurry obtained was treated according to Example 1 with direct steam at a temperature of 145 C The viscosity of the adhesive slurry obtained was 3500 to 4000 mPas (cP) measured at 25"C.

Example 5

13 kg of wheat starch fraction which besides starch contained 3.4% by weight of pentosanes and 4.3% by weight of proteins, were suspended in 85 1 of water and treated according to Example 1 with direct steam at 1600C.

Thereafter 2.5 kg of kaolin was mixed into the slurry. The viscosity of the adhesive was 1000 to 1500 mPas (cP) measured at 25"C.

WHAT WE CLAIM IS: 1. A method of manufacturing a starch

containing paper bag adhesive comprising bringing the starch into a substantially water soluble form by mixing the starch or a starchcontaining aqueous slurry having 5% to 30% by weight starch, at a temperature of 1200C to 200"C at super atmospheric pressure whereby the viscosity of the final adhesive is 700 to 5000 mPas (cp) measured at 25"C with a Brookfield viscosimeter using spindle No. 4 and a speed of 20 r/min.
2. A method as in Claim 1, wherein the said viscosity is 1000 to 3000 mPas (cp).
3. An adhesive when prepared by the method as in Claim 1.
4. An adhesive as in Claim 3, comprising, in addition to starch, mineral fillers and known additives.
5. An adhesive as in Claim 4, wherein the fillers and additives are inorganic bases, borax, carboxy methyl cellulose, synthetic resins and polymer dispersions.
6. An adhesive as in Claim 4 or Claim 5, wherein 5% to 30% by weight kaolin is provided calculated on the basis of the dry matter of the adhesive. ~~~~~~~~~~~~~~~~~~~~
7. An adhesive as in any of Claims 4 to 6, wherein 0.1% to 2% by weight sodium hydroxide is provided calculated on the basis of the dry matter of the adhesive.
8. An adhesive as in any of Claims 4 to 7, wherein 0.1% to 10% by weight borax and 0.1% to 10% by weight carboxy methylcellulose is provided calculated on the basis of the dry matter of the adhesive.
9. An adhesive as in any of Claims 3 to 8, wherein the adhesive is dried after manufacture.
10. A method of manufacturing a starchcontaining paper bag adhesive as in Claim 1 and substantially as hereinbefore described.
11. An adhesive prepared by the method according to Claim 1 and substantially as hereinbefore described.