NO762527L - - Google Patents

Description

"Adhesive and: method for

manufacture thereof".

The invention relates to starch-based corrugating adhesives and methods for their production. The invention also relates to methods for tying together objects, in particular laminated objects of fibrous cellulose tissue, and more particularly the production of cardboard for use in the production of corrugated containers. The invention also relates to objects produced using the new adhesive preparations.

One common method of making corrugated board consists of corrugating a paper strip using a corrugated roller, applying an adhesive to the ends of the grooves in the corrugations on one side, and gluing another paper strip, called a "liner", to the groove ends by application of heat and under high pressure.

This product, called "one-sided" corrugated cardboard, can be used as is. However, it is common to make "double-sided", also called "double back" cardboard by sending the single-sided piece of cardboard into the second stage of the corrugator called the "double backer" stage. The term "single facer" generally refers to the first stage in the machine. An adhesive is applied to the opposite groove ends, and another paper layer ("liner") is glued to said opposite side using heat and under a relatively low pressure. The fact that the application of a high pressure in gluing the second paper strip would tend to crush the corrugations makes the gluing problem in the second step quite difficult.

Starch-based corrugating adhesive compositions have been in widespread use since the advent of Stein-Hall's technology, which is described in US Patents 2,051,025 and 2,102,937.

A Stein-Hall type adhesive is an aqueous two-component system. One component of this system is generally made from a cooked or gelatinized starch material, which serves as a carrier phase. Other materials that can form relatively viscous, aqueous slurries, e.g. carboxymethyl cellulose, can also be used as carrier phase.

The second component or phase is made from a raw, ungelatinized starch material. This second phase is a latent or potential adhesive phase. That is, the adhesive characteristics of such a preparation are not fully developed until after the adhesive has been applied to the ends of the grooves in the corrugated fabric, the "liner" has been pressed against the adhesive-coated grooves and heat and pressure have been applied. The heat causes the granular starch material to gelatinize and develop its structure.

The swelling and gelatinization of the latent adhesive phase takes place when the newly assembled corrugated sheet is passed through a hot sheet drying system associated with a corrugator. This system also partially dries the corrugated sheet and causes the adhesive to harden sufficiently to allow it to be subjected to subsequent operations, e.g. trimming, splitting and sheeting without delamination.

The first degree of adhesiveness in the bond in the corrugated board is referred to as the "green" bond strength. This characteristic determines the ability of the newly formed corrugated sheet to withstand the instantaneous high shear forces developed during subsequent processing operations, e.g. the trimming, splitting and sheeting, and is not necessarily an indication of the final bond strength.

"Green" bond strength, or for convenience "green" strength, is a major limiting factor that governs the operating speed at which corrugated sheets can be produced on a particular machine. An experienced machine operator will often run a machine at the highest speed possible without the sheet delaminating during trimming, splitting or sheeting. Since the resistance to delamination is a characteristic that is directly dependent on "green" strength, the characteristics of the corrugator adhesive play a direct role in the efficiency of the machine, which in turn determines the return rate of the fixed equipment that the machine represents.

After the corrugated board is trimmed, split and sheeted, it is stacked and sent to storage, where the adhesive hardens to full strength. until the bond is dry and fully cured, the corrugated sheet can be delaminated by slowly and firmly pulling the "liner" away from the corrugated sheet.

Since the mid-1930s, one of the major advances made in the field of corrugation adhesive technology is that disclosed in US Patent No. 3,355,307. This patent discloses a single-phase corrugating adhesive referred to as a "non-carrier" system, where partially swollen starch granules are present as a homogeneous phase, suspended in an aqueous, alkaline solvent. The elimination of the carrier phase made it possible to achieve significant operational economic results. The non-carrier type corrugation adhesive disclosed and protected in US Patent 3,355,307 was applied and cured in the same manner as the Stein-Ha11 type adhesive preparations.

Other technical advances in the field of corrugation adhesives primarily concerned building in moisture resistance, generally by adding synthetic resins, e.g. of urea/formaldehyde, phenol/formaldehyde and • resorcinol/formaldehyde.

US Patents 2,051,025 and 2,102,937 represent. represented a significant technical advance in its time. The patentee reported that the use of his adhesive systems allowed the operation of corrugated board machines up to 20% faster than would be possible using the previously known adhesive compositions. The adhesive compositions known from the prior art included compositions which were based on sodium silicate and such which were based on the use of gelatinized starch or modified starch, e.g. dextrins.

In the Stein-Hall type system, according to the above US patents, the time required to form an adhesive bond between the corrugated "interliner" and a "liner" or "facer" sheet was essentially regardless of the rate at which the moisture in the adhesive is driven off by heat or absorbed by the paper. According to the aforementioned patents, the time required to form the adhesive bond depended mainly on the time required to effect gelatinization of the granular starch particles suspended in the gelatinized starch carrier phase. As this granular starch gelatinized, water was taken up and the viscosity of the adhesive increased rapidly, forming an instant "green" bond. The patentee believed that tapioca, rye and potato starches were inherently much better than corn, wheat and rice starches for making "corrugating adhesives in accordance with his inventions.

The patentee described 4 main factors that he studied to determine the starch's suitability for use as the latent adhesive component in his system. These 4 factors were: 1. The time required for complete gelatinization of its granular starch by the application of heat on the corrugator.

2. The temperature at which the starch gelatinizes.

3. The viscosity that develops after gelatinization. 4. The degree of stickiness that developed after gelatinization.

However, later developments indicate that the "green" bond strength is significantly dependent on the evaporation of moisture from the bonding site, cf.Thayer&Thomas: Analysis Of the Glue Lines in Corrugated Board; TAPPI; 22nd Corrugated Containers Conference, May 1971..

It has now been discovered that a selected class of starch materials exhibit superior properties when used as an adhesive component in a corrugating adhesive preparation. One; way to take advantage of these properties is to use machine speeds that are ordinarily from 50 to 100% higher than what has been considered possible with conventional corrugation adhesive preparations of the Stein-Hall type, or with the more recently introduced non-carrier corrugating adhesive preparations, at generally the same levels with regard to adhesive use.

Put another way, superior results have been obtained when the primarily active adhesive component in a corrugating adhesive preparation is a saponifiable starch ester material which exhibits at least approx. a 30% larger area under an Instron power/time heating curve and at least approx. 30% greater area under an Instron force/time cooling curve, compared to unmodified corn starch under the same test conditions.

Preferred adhesive preparations according to the invention are based on the use of primary adhesive components which are saponifiable starch esters with a saponifiable degree of substitution (D.S.) of at least about 0.015. As used herein, "saponifiable degree of substitution" means the total D.S. for all saponifiable ester groups on the starch molecule. Particularly preferred starch ester materials are starch acetate, starch succinate and

in

starch acetate succinate. One or more of these active adhesive components can be advantageously used either in a Stein-Hall type recipe or in a non-carrier type recipe, with equally superior improvements in relation to the state of the art.

The most preferred adhesive component is a starch acetate succinate having a saponifiable degree of substitution (D.S.) in the range of about 0.025 to approx. 0.045. These D.S. levels represent ranges applicable to starch acetate succinate. Other derivatives useful in accordance with the invention will have their own preferred D.S. regions. In general, if the D.S. level is too low, the derived material will not exhibit sig-. significant improvement over unmodified corn starch when used in a corrugation adhesive preparation. If the D.S. level is too high, then the gelatinization temperature may be unusable.

The specific material identified for use in accordance with the invention is the starch derivatives identified above. These starch derivatives can be prepared immediately before use, i.e. in situ on the corrugator, or they can be prepared in advance and mixed into corrugator adhesive preparations like other starch materials to be used for such purposes in accordance with previously known practice.

It is also possible to use modified starch materials which can be produced from the starch esters mentioned above. These modified starch materials are produced by essentially completely saponifying the starch esters and removing the salts that are thereby formed. The resulting modified starch material can then be dried. Although the derivative has been essentially completely removed from the starch material, the modified starch retains the beneficial properties of the ester material.

Although the reason that the special materials that

have been identified by the present invention, are not fully understood with respect to their being superior for use especially for corrugation adhesives, it can be theorized that they not only develop unusually high viscosity upon gelatinization, but that they additionally provide high "green" strength without the necessity of solvent evaporation.

Although the final form of the useful starch materials according to the invention is not known, it is known that the ester materials saponify substantially completely within a short period of time in the environment present in the mixing apparatus in the corrugator.

The invention will be better understood by a more detailed explanation of various specific embodiments. All parts and percentages are by weight, on a commercial basis, unless otherwise expressly stated. The commercial basis for the starch materials includes approx. 12% humidity.

The correct selection of the primary active adhesive component is of great importance for the correct implementation of the invention. In the manufacture of saponifiable starch esters for use as the primary active adhesive components, the initial . the starch material is taken from any vegetable source. Starch derived from non-waxy grain sources, e.g. corn, wheat, rice and sorghum are preferred. The term "starch" is used here roughly to include flour, unmodified starch and return grains, so-called "tailings". Corn starch is a preferred starting starch material.

The starting starch is esterified, as will be described,

for the preparation of the primary active adhesive component which

have the desired characteristics in accordance with the invention.

In a typical corrugation adhesive preparation, it is usual to add forax and caustic soda to increase the adhesive strength and stickiness, and to adjust the gelatinization temperature. When using an adhesive composition of either carrier type or non-carrier type, the Stein-Hall viscosity of the composition must be within the conventional range to enable an adequate amount of adhesive to be applied to the groove ends at all machine speeds. To be stretchable on a corrugator, an adhesive preparation must generally have a Stein-Hall viscosity in the range from approx. 20 to approx. 100 seconds. The Stein-Håll viscosity of the preparation will depend on the particular corrugator.

Unless otherwise stated, the materials are as here

are described, such as must be added to form the adhesive preparation. In the special environment of the adhesive preparation, the shape of certain materials can be changed. For example, the starch ester will saponify in a typical corrugation adhesive preparation.

This will reduce the current amount of alkali present. The borax can be present in different forms or as an equilibrium mixture of these forms, primarily depending on the preparation

PH value.

As previously described, it is standard practice in the corrugation industry to add alkali and borax to the adhesive preparations. Although preparations which do not include these materials can be used as corrugation adhesives, it is preferred to include both of these materials in the preparations according to the invention.

The borax is generally used to increase the gel structure of the adhesive paste. However, an excess of borax can have an adverse effect on the cure bond strength. In addition, borax tends to increase the preparation's gel temperature. In general, up to approx. 5% borax (10 mol) is incorporated into the preparations.

A more common amount would be approx. 2% to approx. 3%. The percentages

is based on the total starch material present in the preparation, including both the primary active adhesive material and the carrier material. If 5 mol of borax is to be used instead of 10 mol, it is necessary to compensate for the reduced water of hydration. In non-carrier systems, boric acid can be used as a reaction stopper. The boric acid will quickly be converted into a borate and is then able to serve as a substitute for added borax. In this context, the term "borax" will include those borates that are present due to the addition of boric acid.

Any standard alkali can be used. However, sodium hydroxide is usually used, for economic reasons. The alkali serves to reduce the gel temperature of the adhesive preparation to an easily stretchable point. In general, this will be in the range from approx. 62.8°C to approx. 65.5°C, but for some purposes can vary from approx. 60.0 to approx. 71.1°C. It is important that large amounts of alkali are not used in any corrugation adhesive preparation, whether conventional or in accordance with the present invention, as alkali tends to reduce gel structure formation. In general, up to approx. 5% alkali (calculated as sodium hydroxide) is used, based on total starch material in the system. More common amounts would be from approx. 3 to approx. 3.5%.

It is of critical importance for the performance of the invention that at least sufficient alkali to practically completely saponify the starch ester is used. The amounts of alkali that are referred to above are the amount of alkali that is in excess of this minimum amount.

The particular starch ester to be used in carrying out the invention is not critical, as long as it will saponify in the environment of a corrugation adhesive preparation. Accordingly, starch esters which are not expensive and which are simple are preferred, e.g. starch acetate. Particularly preferred is the mixed ester, starch acetate succinate.

The starch esters can be obtained commercially, or they can be made by any conventional method, e.g. by conversion of unmodified starch with acid anhydrides, acid halides, vinyl esters and the like. The same reagents can be used when using the in situ method according to the invention. However, it is necessary that the esterification is carried out at a temperature which is below the relevant gelatinisation temperature for both the unmodified starch and the starch ester.

Furthermore, the water content of an adhesive preparation must be adjusted so that an extremely tacky adhesive characteristic is obtained immediately after gelatinization. This means that sufficient water is present for complete gelatinization. It is most desirable that rapid development of adhesion is achieved by the application of heat in the corrugation equipment.

The amounts of starch materials used in the adhesive preparations according to the invention are similar to those used in conventional preparations. In general, the granular starch component in a Stein-Ha11-type preparation will contain from approx. 10 to approx. 25% starch. The final adhesive mixture generally has from approx. 12 to approx. 25% of its total starch in the form of the gelatinized carrier.

The starch esters according to the invention can also be used as the carrier part in an adhesive of the Stein-Hall type.

In such cases, it may be possible to reduce the amount of carrier somewhat due to the greater thickness of these starch esters.

The desired degree of substitution depends on the particular starting starch material that is chosen. However, it has generally been found desirable to use a saponifiable D.S. of at least approx. 0.015. Starch esters that have a saponifiable D.S. of at least approx. 0.015, has been shown to satisfy the Instron test criteria, discussed above, thereby allowing machine speeds of at least approx. 20% greater than those obtainable using unmodified corn starch as the primary active adhesive component.

In general, D.S. levels higher than 0.015 will give even greater machine speeds. It has been shown to be preferable and to use saponifiable starch esters which have a saponifiable D.S.

in the area from approx. 0.025 to approx. 0.045. The use of such materials will generally allow the operation of a corrugator

at speeds up to approx. 100% higher than those achievable using conventional adhesives.

The "green" strength, and the viscosity of the gelatinized corrugation adhesive that produces the "green" strength, cannot be conveniently subjected to direct quantitative measurement at the precise point of adhesion. However, it appears that the inherent ability of a corrugation adhesive to produce higher "green" strength, which allows improved corrugation speeds, can be predicted by a measurement of the area under an Instron force/time curve for a paste made in one particular way from it primary active adhesive component selected for application Inconsistency with the invention.

The Instron force/time curve for a paste of a primary active adhesive component can be determined in accordance with the following procedure.

STANDARD INSTRON METHOD

An Instron Tensile Tester Model TT is equipped with a compression loaded cell "CM". A cultivation tube approximately 22 mm in diameter and 175 mm high is fitted into a constant temperature chamber. This chamber is a metal stocking approximately 23 mm in diameter and 116 mm high, wrapped with approx. 1.2 m of 4.5 mm copper pipe and covered with asbestos. The copper pipe is connected to a constant temperature bath at suitable inlets.

The starch slurry to be tested is placed in the cultivation tube to a depth of 7 cm.

The cultivation tube is lowered into the stocking, which is preheated by circulating water at a temperature of 98.9°C through the copper tube. A thermocouple probe that has a diameter of 4.7 mm is inserted approx. 2.5 cm deep into the top surface of the slurry. At the same time, turn on the machine and the recorder, the probe being driven into the slurry at a speed of 0.5 mm/min. This heating cycle is continued for 14 minutes, after which the hot water circulation is stopped. After one more minute, ice water is circulated through the tube and this is continued for 15 minutes.

The curve drawn on the recorder is called a force/time curve. The first 15-minute segment shall be referred to as the warm-up cycle and the second 15-minute segment as the cool-down cycle.

The test slurries for use on the Instron instrument are made as follows: A predetermined amount of unmodified corn starch is slurried in 110 ml of water. A predetermined amount of a 4% w/v borax (10 mol) solution and a predetermined amount of a 20% w/v NaOH solution are added. Sufficient water is added to give a total additional volume of 60 ml. The resulting slurry is heated at a temperature of 100°C, with stirring for 5 minutes, and then allowed to stand for 5 minutes. It is then added immediately to the other slurry that has been prepared in advance"

The second slurry is prepared by slurrying 50 g of the test starch in 165 ml of water. The first slurry is then mixed with this slurry, and the whole mixture is stirred for 15 minutes. The mixture is then tested immediately on the Instron tester.

A sample of unmodified corn starch is run as test starch under these standard test conditions. The power/time heating and cooling curves are developed as described above, and the area under each of these segments is determined independently.

The identical process is then followed for the starch material to be tested. The areas under the heating curve for the test starch are compared with the area for unmodified corn starch. The same is done for the areas under the cooling curve. It must be pointed out that the areas under each of the segments in the curves are treated independently of each other.

The absolute areas determined in this way are arbitrary values largely determined by the test process. The decisive feature of the test is not these absolute values, but the ratio between the areas for the test starch and the areas for the unmodified maize starch, when carried out under the same test conditions. This means that the predetermined amounts of carrier starch, borax and sodium hydroxide are identical.

Although the Instron test is not completely reproducible in terms of the viscosity and gel structure of the adhesive line, it provides a relative measure of the ability of a particular primary adhesive component to develop high "green" strength in a corrugating bonding environment.

It has been shown that to produce the desired

20% improvement in machine speed, the ester material must show at least approx. a 30% larger area under both instron heating

and -cooling curves compared to unmodified corn starch. In other words, a saponifiable starch ester that will exhibit a

30% Instron improvement (larger area) under both heating and cooling curves will give machine speeds of at least approx. 20% higher value than machine speeds achievable using unmodified corn starch, on the same machine.

The useful starch ester materials can also be defined as having a total saponifiable degree of substitution (D.S.) of at least approx. 0.015. This upper limit for saponifiable D.S. is

economical and functional. It is necessary that the material has a gel temperature that is high enough so that it will not gelatinize before use, e.g. during production of the derivative or during mixing of the adhesive preparation.

Although the exact upper limit of saponifiable D.S. will depend on the particular substituent used, generally speaking, then for esters of monocarboxylic acids it will be approx. 0.1 and for monoesters of dicarboxylic acids approx. 0.06.

It is known that in the environment of the adhesive preparation, the ester will saponify within a relatively short time. This means that the ester will be substantially completely saponified before it is applied to the groove properties. The exact form of the saponified starch material is not known. It is possibly a complex with either the caustic soda or the borax generally present in the system.

It is believed that part of the improvement in machine speed can be attributed to a reduced alkali level in the preparation. As the ester material saponifies, some of the alkali is used up.

Some of the beneficial properties of the starch esters. preserved in the saponified product. Before it is actually applied to the groove ends, the ester is practically completely saponified. It has been shown that a modified starch material can be produced by saponification of the starch ester. The saponification is carried out in the presence of alkali and can further include borax in the saponification medium. The modified material can then be dried. This process, i.e. the esterification followed by saponification, gives a material which is different from the original unmodified starch material. This modified material can be used in a corrugation adhesive preparation in a manner similar to the use of the starch esters. Improved "green" bond strength compared to unmodified corn starch has been found. The exact mechanism of the modification is not known, but may be a physical splitting of the granules, or it may be a small amount of a complex which

is formed between the alkali and the starch.

The use of a reduced amount of alkali in the corrugation adhesive preparation does not account for the entire machine speed improvement. When unmodified corn starch and a starch ester in accordance with the invention are run at identical current alkali levels, machine speeds are still much greater using the starch ester materials.

The starch esters can be formed in situ at the corrugator when producing the adhesive preparation. It is only necessary to add an ester-forming reagent to the preparation. The conditions are such that will allow very rapid esterification, followed by irreversible saponification. The esterification reagents are the above-mentioned conventional materials. The amount of reagent to be added is that which, in the absence of saponification, would give a product with a saponifiable D.S. suitable for use in accordance with the invention.' In general, such a reagent as acetic anhydride will have a reaction efficiency of approx. 50% to approx. 70% under the conditions encountered in a correction adhesive preparation.

The order of addition of the materials to the adhesive formulation is not critical to the success of the stated in situ method. It is of course necessary that the esterification reagent not be allowed to remain in an environment for any particularly long time where it could, at least partially, be decomposed.

To more fully understand the invention, reference is made

that to the following description of specific embodiments of the invention. The examples are intended as an illustration and for information, but not in any way to limit the scope of the invention.

EXAMPLE I

Comparative. production trials with corrugated sheets

In order to show that the corrugation adhesives according to the invention provide improvements compared to conventional adhesive preparations containing unmodified starch, of the Stein-Hall type, it was necessary to establish a limit above which speed conventional starch adhesives no longer debond the corrugation plate sufficiently to to prevent delamination during the subsequent operations, and then to determine at what machine speed corrugated sheets using adhesives prepared in accordance with the invention could be produced before they reached the point of failure.

The corrugated sheets produced in all tests

in this example, a so-called "double backer" plate consisting of an 11.8 kg corrugated sheet was sandwiched between two 19.1 kg Kraft liners. A commercial "double-backer" corrugated paper machine was used. All hot plate temperatures were set at 148.9°C for this experiment. Initially, the glue clearance on the adhesive applicator was set at 0.36 mm. A conventional corrugation adhesive of the Stein-Hall type, for use as a control, and corrugation adhesive preparations prepared in accordance with the invention, were made as indicated in the table below.

Conventional "Double Backer" recipe

Primary mixer

Add 37.85 1 water

Add 9.1 kg of unmodified cornstarch

o

Heat to 65.5 C

Add 1.5 kg NaOH dissolved in 7.57 1 water

Stir for 15 min.

Then add 3 7.85 1 cooling water

Mix for 10 minutes and hold at 43.3°C

- Secondary mixer

Add 113.55 1 water and heat to 32.2°C

Add 1.54 kg (10 mol) of borax

Add 45.4 kg of unmodified cornstarch

Add the primary mixture to the secondary i

during 30 minutes and hold at 43.3°C

Adjust the viscosity to 60 sec. with 17.0 1 water "Double Backer" recipe according to the invention Primary mixer

Add 37.85 1 water

Add 8.6 kg of unmodified corn starch Heat to 65.5°C

Add 1.8 kg NaOH dissolved in 7.57 1 water Stir for 15 min.

Add 37.85 1 cooling water and hold at 43.3°c

Secondary mixer

Add 113.55 1 water and heat to 32.2°c

Add 0.7 kg (10 mol) of borax

Add 45.4 kg of starch acetate succinate (0.027 D.S. acetate, 0.01 D.S. succinate). Add the primary mix to the secondary over 30 min. and hold at 43.3°C Mix for 5 minutes and add 0.7 kg (10 mol) borax Add 17.0 1 water to adjust viscosity to 60 seconds

The adhesive properties of these preparations were determined and are listed below.

"Double Backer"

Adhesive properties

Both of these adhesive preparations were assessed one after the other on the same corrugator.

Using the control adhesive indicated above, the maximum speed attainable on the corrugator before the corrugated sheet began to delaminate at the cutter was 135 m/min.

Using the starch acetate succinate as the crude starch component in the Stein-Hall type double backer adhesive formulation, speeds of 180 m/min were achieved. At this point, the glue clearance on the double backer applicator was increased from 0.36 mm to 0.41 mm, and the corrugator was run at 210 m/min, or 55% better than the control, with excellent double backer-" green" strength. Above this speed, the "single facer" corrugator, which fed single-sided corrugated paper to the "double backer", would not. keep pace due to the fact that the adhesive preparation used in the "single facer" step was a typical conventional unmodified starch adhesive, and not enough heat could be applied by the machine to cause sufficiently rapid gelatinization of said adhesive.

However, with the "single facer" bridge full of plates made at lower machine speeds, the "double backer" section could be run in short spurts at speeds well over 240 m/min. The limitation of these runs occurred when unbonded "single facers" sheets would reach the "double backer" glue machine. It is. therefore, it is obvious that the starch acetate succinate adhesive will give good "double backer" corrugated sheets at corrugator speeds significantly above 210 m/min.

EXAMPLE II

Production trials with corrugated sheets

A further corrugation test was carried out using the same corrugation machine and essentially the same operating conditions as for the experiments in example 1. The machine was used for the production of plates using 19.1 kg of liner and a 11.8 kg corrugated medium, with glue clearances of 0.33 and 0.36 mm.

The starch derivative used as the primary adhesive component was characterized as follows: It was a starch acetate succinate with a D.S. for acetate = 0.011; D. S. for succinate = 0.015. It was found that an adhesive composition prepared as described below could be run successfully at fairly high machine speeds. The composition was as follows:

With the glue deposits set at 0.33 mm, the corrugator could be run efficiently at 210 m/min. Lowering the glue clearances to 0.23mm allowed sustained corrugator speeds in excess of 240m/min to be achieved. At this point the corrugator had reached its practical limit, and 28.2 kg liners were then used instead of the 19.1 kg liners.

With -the heavier liner, the corrugator efficiently produced corrugated sheets at speeds of 195 m/min. at a setting of 176.7°c on the corrugator's heating plates. Conventional starch adhesives have a limit of 90-150 m/min. at 148.9°C and 105-120 m/min. at 176.7°c hot plate temperatures when using these liners on this machine. The corrugation efficiency was significantly superior when using the preparations according to the invention.

EXAMPLE III

Further production trials: Stein-Hall recipes Further trials were carried out on the same machine in accordance with the last mentioned method from Example II using 28.2 kg of liners with primary adhesive components characterized as follows: Starch derivative.

Starch acetate succinate

(D.S. for acetate = 0.013;

D..S. for succinate = 0.016)

Starch acetate succinate

(D.S. for acetate = 0.018;

D. S. for succinate = 0.014)

The starch derivative identified as (a) was prepared as an adhesive preparation as described in Example II. and used on a corrugator with glue clearances of 0.18 mm with the hotplate set at 148.9°C. Starting machine speeds of 180 m/min. was achieved. As the glue clearance was opened to 0.25 mm, machine speeds of up to 225 m/min were achieved. When hotplate temperatures were raised to 176.7°c, machine speeds of 232.5 m/min were achieved, with satisfactory plate production.

When running an adhesive preparation as described

in Example 2, using the starch derivative identified above as (b), on the corrugator with the glue clearances of 0.18 mm, and the hotplates set at 176.7°C, corrugated sheets were successfully produced at 240 m/min .

EXAMPLE IV

Preparation of non-carrier type

A small-scale demonstration was carried out with an adhesive preparation (IV-1) containing 18-20% starch acetate succinate (D.S. for acetate = 0.0266; D.S. for succinate = 0.018)

as the primary adhesive component, in an aqueous slurry. This is equivalent in composition to a conventional 11-sack mixture in a mill (ie, equivalent to a preparation containing 11 bags of the adhesive component in approximately 2,460 1 of total adhesive).

Another demonstration was performed with an adhesive formulation (IV-2) made from a mixture of unmodified corn starch and the primary adhesive component, in such proportions that on a mill scale 2 of the 11 sacks (ie, about 18%) would be unmodified corn starch, the remainder being the primary adhesive component.

Stein-Hall viscosity measurements were performed on each of these preparations after they were ready for use. The preparation process was that described in US Patent 3,355,307, and was as follows: 250 g of starch material was slurried in 890 ml of water at 40.6°C. 2 75 ml of 4.0% sodium hydroxide (caustic) was added to the starch slurry at room temperature over 4.5 minutes. The reaction was quenched at 600 cP with 4.7 g of boric acid. The resulting paste in each case consisted of a substantially homogeneous suspension of partially swollen granules.

The Stein-Hall viscosity observations were made immediately, and then, after each preparation had been stored for 24 hours, at 37.8°C with gentle stirring. The viscosities were similar to those of typical conventional preparations.

EXAMPLE V

An adhesive preparation with the following composition was produced:

Primary mixer

Water 378.5 1 Unmodified corn starch 100 kg

NaOH (dissolved in 37.85 1) 18.2 kg

Heat to 71.1°C and hold there for 15 min.

Water 2 50 1

Secondary mixer

Water 143.51

Borax (10 mol) 8.2 kg Starch acetate succinate 454 kg

Mix in primary mix

within 30 minutes

Water 75.7 1

Borax (10 moles) 45.4 kg

This preparation was run on a commercial machine using a 40.8kg liner on the single face side and

two 40.8 kg liners laminated on the machine on the "double backer" side. Good debonding was observed at speeds of 106 m/min. Conventional adhesives can normally be run at approx. 60-75 m/min. under the same test conditions.

The same mixture was used as a laminating adhesive with satisfactory results. however, no numerical data were obtained as this particular machine could be run at its top speed using either a conventional formulation or a formulation in accordance with the invention.

EXAMPLE VI

Another batch of adhesive was prepared using the same starch acetate succinate as indicated in Example v. The amount of carrier starch was 95 kg, and the rest of the preparation was identical to that indicated in Example 5.

Using the identical 90, 90/90 laminate, with liners as indicated in Example 5, speeds of 126 m/min were achieved. A further attempt was made where the "double backer" liner consisted of a 40.8 kg liner laminated on the machine using this adhesive formulation to a 31 kg liner. Speeds of 123 m/min. was achieved. The average speeds for both of these plate grades were 60 m/min. using conventional adhesives. Machine speed was not limited in these two cases by glue line failure, but by the possibility of running with overload at higher speeds.

EXAMPLE VII

To a slurry of 24.6 g of unmodified corn starch in 330 ml of water was added 25 ml of a 2.75% (w/v) borax solution, 45 ml of 3.09% (w/v) NaOH and a mixture of 0.018 mol succinic anhydride and 0.048 mol acetic anhydride. A laboratory evaluation of the resulting slurry indicated that it had superior adhesive properties.

EXAMPLE VIII

Example VII was repeated with the exception that the succinic anhydride was replaced by adipic anhydride. The product was again rated as a superior corrugation adhesive.

EXAMPLE. IX

Commercial trials were carried out on a number of products using the following preparations.

When using the ester materials, NaOH was added to

9.1 kg and the borax to 8.2 kg.

The preparations were run using 2 7.2 kg liners with glue settings of 0.51 mm on "single facer" and 0.46 mm on "double backer".

EXAMPLE X

Instron force/time curves were produced using the standard method for the following starch materials.

(a) This is material from Example IX, Experiment 2

(b) This is material from Example IX, Experiment 3

(c) This is material from Example IX, Experiment 4

(d) This is material from example i

(e) This is material from Example V

(f) This product showed only 13% machine speed improvement (g) This is material from Example III, trial a (h) This is material from Example III, trial b (i) This product showed 38% machine speed improvement

EXAMPLE XI

Standard Instron force/time areas were determined for the following starch materials:

EXAMPLE XII

The material from Example I was saponified in the presence of NaOH and borax. It was then washed with water to remove the caustic soda, borax and salts. A standard Instron force/time determination was made. The material showed 58% heating cycle improvement and 82% cooling cycle improvement.

EXAMPLE XIII

Example XII was repeated using material from Example V. This showed a 58% improvement in the heating cycle and a 102% improvement in the cooling cycle.

When an acid neutralization step was introduced, no significant improvement was demonstrated in comparison 'with unmodified corn starch.'

Although the starch acetate succinate, and the other specific primary adhesive components identified herein, provide superior results compared to compositions based on unmodified corn starch and other conventional materials, they can generally be used in the preparation of corrugation adhesive compositions in the same general manner and substantially the same conditions such as conventional materials, e.g. unmodified corn starch. In general, the primary adhesive components according to the invention can be used to replace part of, or: preferably all, of the conventional primary adhesive components in adhesive preparations of both Stein-Hall type and non-carrier type. Specific variations in amounts of components and the addition of other components can be made in the preparations using these primary adhesive components in the same way as is done for conventional adhesive preparations. These variations are well known to those skilled in the art.

The details of the Stein-Hall type adhesive system can be found in the above-mentioned US Patents 2,051,025 and 2,102,937, the descriptions of which are incorporated herein. The details of non-carrier type adhesive systems can be found in US Patent 3,355,307 , which is included here. When using the applicant's new preparations in a non-carrier environment, such reaction stoppers as acid anhydrides and acid chlorides can be used. These can be roughly defined as acid or acid-producing materials. Careful selection of the reaction stopper can thus allow the same material to serve as reaction stopper and esterification reagent.

It is of course necessary that the final bond strength, as opposed to the "green" bond strength, is sufficiently high to enable conventional use of the product. Needle adhesion tests have shown that the final bond strengths using the adhesive preparations according to the invention are practically equal to bond strengths for conventional adhesives.

The adhesive preparations according to the invention are also useful for purposes other than the production of corrugated cardboard. For example, these preparations can be used in pipe winding and the production of laminated boards and multi-layer paper sacks.

Furthermore, the conventional additives which will give water resistance to the hardened bonds can also be incorporated into the preparation.

Although the invention is described in connection with specific embodiments thereof, it shall be understood that it may be subject to further modifications, and this application shall cover other variations, applications or adaptations of the invention by generally following the principles of the invention and including such deviations from present description which is within known or common practice in the area to which the invention belongs, and which can be applied to the essential features which are indicated here, and which are within the scope of the invention.

Claims (8)

1. Adhesive preparation which is suitable for use in a corrugator and which makes it possible to run the corrugator at operating speeds of at least approx. 20% above what is possible when using unmodified maize starch as the primary active component, characterized in that the preparation contains as the primary active component a saponifiable starch ester material which has at least approx. 30% larger area under an Instron power/time heating curve and at least approx. 30% greater area under an Instron force/time cooling curve, compared to unmodified corn starch under the same test conditions, and sufficient alkali to practically completely saponify the saponifiable starch ester material. 2.K pharmaceutical preparation as specified in claim 1, characterized in that the saponifiable starch ester material .. has a saponifiable D.S. value of at least approx. 0.015. 3.K pharmaceutical preparation as stated in claims 1 and 2, characterized in that the saponifiable starch ester material is a saponifiable corn starch ester material. 4. Adhesive preparation as stated in any one of claims 1 to 3, characterized in that for saponable starch ester material is granular and ungelatinized. 5. Adhesive preparation as stated in any of the preceding claims, characterized in that the saponifiable starch ester material is in the form of partially swollen granules. 6. Adhesive composition as set forth in any one of claims 1 to 5, character! characterized in that the saponifiable starch ester is selected from the group consisting of starch acetate, starch succinate, starch acetate succinate and mixtures thereof. 7. Adhesive preparation as set forth in any one of claims 1 to 6, characterized in that the saponifiable starch ester is a corn starch acetate succinate with a saponifiable D .S. value in the range from about 0.025 to about 0.045. 8. Adhesive preparation as specified in any of the preceding claims, characterized in that it contains up to approx. 5% additional alkali and up to approx. 5% borax (10 moles), based on total starch material, commercial basis.