NO136462B - - Google Patents

Description

The manufacture of corrugated cardboard usually includes the following steps:

in a first step, a paper tap, which is usually moistened, is passed between heated, fluted cylinders. An adhesive is then quickly applied to one side of the paper which is correspondingly fluted and constantly heated, and then placed immediately after a paper web, which is usually called a cover layer, on the fluted surface with adhesive. This operation is usually carried out under heating and pressure. A material that consists is thus obtained

of a flat side and a fluted side, the two surfaces being fixed together at the level of the flutes with adhesive. This material is usually called single-sided corrugated cardboard.

If one applies adhesive to the free riffles of the single-sided corrugated board and covers these riffles with another cover layer, a double-sided corrugated board is obtained. It is also possible to produce double-double-sided corrugated board by combining a double-sided bblge board with a single-sided corrugated board (against the grooved part of the latter) and in a similar way triple-sided cardboard.

Due to the high speeds at which the available industrial machines can work (more than 200 m/min.), the primary properties that the joining agent must have are a satisfactory "adhesion" and a fast fixing ability. The term "adhesion",

which is often used in this industry can be defined as the property of an adhesive that is able to form a

sufficient bond immediately after the adhesive and the substrate are brought into contact with each other under light pressure. The adhesiveness should usually appear in the course of approx. 0.1 sec. Adhesion can be defined as the ability of an adhesive to form a bond between the "cover layer" and the "rifle layer" that is not affected by sudden movements of the cardboard. An attachment ability is fast if it occurs within 1 - 5 seconds. after the application of the jointing agent.

In general, it can be said that the known adhesives have this rapid adhesion property to varying degrees. These adhesives are usually made from soluble silicates, such as e.g. sodium silicate (SKEIST - HANDBOOK OF ADHESIVES - 1962 page 92), gelatinized starch or mixtures of non-gelatinized starch and an agent which acts as a carrier for this "raw" starch, such as e.g. gelatinized starch (US Patent 2,102,937).

In order to achieve improvement of certain properties such as e.g. resistance to water of the paperboard obtained, it has also been proposed to use mixtures based on starch materials and a thermo-curable resin such as e.g. urea-formaldehyde or melamine-formaldehyde (French patent document 1,585,311) or also a phenol-formaldehyde resin (Canadian patent document no. 846,239).

The majority of the above-mentioned mixtures have in common that they contain starch, as the only component or as the main component. The disadvantage of such adhesives is that they must always be produced at relatively high temperatures (to cause the explosion of all or parts of the starch). In the production of single-sided corrugated cardboard, the application of adhesive at hqy temperature does not constitute a serious disadvantage since the formation of the ridges can only be carried out on heated rollers and the application of the adhesive is carried out immediately after this formation. On the other hand, if one wishes to produce double-sided corrugated cardboard, double-double-sided corrugated cardboard or a triple-sided corrugated cardboard, the use of adhesives based on starch means that the cardboard sheet must be sent in over heated tables to make it possible to apply adhesive, bursting of the starch and drying the cardboard. For technological reasons, it is also difficult to produce mixtures with a solids content higher than 20 - 30%, and this creates a problem with removing the large volume of water.

Using adhesives "in a cold state", i.e. at a temperature lower than 50 - 60°C, of course makes it possible to avoid the disadvantage of "heating" adhesives based on starch. A mixture that can be used at such temperatures is described in French patent document No. 1,488,773. This mixture consists of a portion of clay in suspension in an aqueous solution containing polyvinyl alcohol, a complex titanium oxalate and ammonium bicarbonate. When this mixture is applied at a temperature of 25 - 30°C will

it always has the disadvantage that it only ensures a weak adhesion of the cover layer to the grooved layer. Also, the mixture has on

due to the acidic pH, there is a tendency to corrode the device for applying the adhesive. Furthermore, the affinity for water of the polyvinyl alcohols leads to joints with relatively poor water resistance.

On the other hand, it has been proposed to avoid the problem of removing the water by using adhesives which are applied in a molten state. Apart from the fact that this technique again raises the problem of hot execution, i.e. with increased energy consumption, it cannot be used in general, but does so with special devices, such as those described in the French patent document 1,532,690.

The present invention makes it possible to avoid the above-mentioned disadvantages. More particularly, the invention relates to an adhesive mixture that can be used in the relevant machines for the production of corrugated cardboard, which can be produced at only a slightly elevated temperature to provide a resistant joint. Furthermore, these mixtures have a very high dry matter content.

The invention thus relates to an aqueous adhesive dispersion, particularly suitable for the production of corrugated board, with a dry matter content of synthetic polymers or copolymers with a particle size between 0.05 and 10 µm, an inorganic filler and optionally a hardenable precondensate of formaldehyde and phenol or an aminoplastic former , and optionally a catalyst for curing the precondensate, as well as optionally a dispersant and/or a plasticizer, and the distinctive feature of the aqueous adhesive dispersions according to the invention is that the dry substance comprises: a) 10 to 90 parts by weight of one or more homopolymers of vinyl acetate or styrene, copolymers of vinyl acetate with at least one monomer having at least one ethylenically unsaturated bond, or copolymers of styrene with at least one monomer having two ethylenically unsaturated bonds, and b) 90 to 10 parts by weight of calcium carbonate with a particle size between 0.1 and 120 µm,

in that the total dry matter content in the dispersion constitutes 50 85 percent by weight of the dispersion, and the precondensate, when present, constitutes 0.1 - 15 percent by weight in relation to the total weight of dry matter, and includes a reaction product of a phenol, urea, N,N '-ethylene urea, dicyandiamide or aminotriazine.

These and other features of the invention appear in the patent claims.

Dry matter content is defined as the percentage by weight of products obtained after heating the dispersion for 1 hour at 105°C in a steam bath (according to standard ISO no. ISO/R - 1625 - 1970 F).

The polymers used are in and of themselves known for use in adhesives. The filler is also, among a number of others, known to be used in adhesives. The special combination that makes up the invention is, however, new, and the invention offers significant advantages, particularly with regard to rapid drying and gluing at low temperatures of layers of corrugated cardboard.

Examples of monomers that can be copolymerized with vinyl acetate include ethylene, propylene, vinyl esters of linear, saturated aliphatic carboxylic acids with more than 12 carbon atoms, preferably between 3 and 12 carbon atoms, such as e.g. vinyl propionate, vinyl butyrate, vinyl laurate, vinyl esters of saturated, aliphatic carboxylic acids with 5-12 carbon atoms and in which the carboxyl group has a tertiary or quaternary carbon atom in the oc-position, crotonic acid, acrylic acid or methacrylic acid as well as alkyl esters thereof with an alkyl group of 1-10 carbon atoms, such as acrylates and methacrylates of methylhexyl, ethyl, butyl ethyl-2-hexyl and amides thereof, such as e.g. acrylamide or methacrylamide, dicarboxylic acids with an unsaturated ethylene bond, such as e.g. maleic acids or fumaric acids as well as their mono- or diesters of alkyl, where the contained alkyl group(s) contain 4-10 carbon atoms, such as e.g. the maleates or fumarates of dibutyl, dihexyl, butyl and hexyl and 2-ethylhexyl.

It should be understood that the copolymers can be obtained from more than 2 monomers. For example, copolymers of vinyl acetate used in the invention may include copolymers based on vinyl acetate and butyl maleate and/or 2-ethylhexyl acrylate, copolymers of vinyl acetate with butyl acetate and crotonic acid, copolymers of vinyl acetate with ethylene and, optionally, with acrylic acid. Mixtures can also be used, e.g. homopolymers of vinyl acetate with a copolymer of vinyl acetate/2-ethylhexyl acrylate. The copolymers usually contain between 50 and 90 weight percent vinyl acetate. If the copolymers contain free carboxyl groups, the proportion of monomer with such groups is usually between 0.1 and 10 percent by weight of the total monomers subjected to the polymerization.

In copolymers of styrene, the other monomer(s) can be selected from among unsaturated monomers with at least two double bonds. Generally, hutadiene is used as co-monomer.

The amount of styrene in these copolymers is usually between

40 and 75 percent by weight.

The production of the various homopolymers and copolymers can be carried out according to known methods.

The above-mentioned polymers and especially the copolymers containing a copolymerized plasticizer, such as e.g. butyl maleate,

can be used. It is also possible to use an additional softening agent. These softeners can be of the type usually used, such as e.g. phthalates, adipates, azelates, sebacates. Dibutyl- or 2-diethylhexyl-

phthalate. If an added plasticizer is used, this usually constitutes between 5 and 50 percent by weight of the total weight of the polymer.

The mixtures according to the invention are available in the form of aqueous dispersions and it is advantageous to use one or more dispersants or stabilizers. This agent, which must be soluble in water, is usually selected from among anionic dispersants or nonionic dispersants.

Examples of anionic dispersants include sodium salts or cesium salts of phosphoric acids (hexametaphosphoric acid), saturated fatty acids with 5 - 18 carbon atoms, sulfonated fatty acid esters, alkyl sulfonates and sodium sulfonates (alkyl groups contain 6-18 carbon atoms), alkylbenzene sulfonic acids and alkylbenzene sodium sulfonates, alkyl sulfonate sodium succinates, alkylpotassium malonates, condensates of ethylene oxide and alkylphenol sulfates.

Examples of non-ionic dispersants include polyvinyl alcohols, hydroxyethyl cellulose, condensates of alkyl phenols or fatty alcohols and ethylene oxide as well as vegetable oils that are polyoxyethylated.

Other dispersants or stabilizers can also be used, such as e.g. those mentioned in "Detergents and Emulsifiers" published in 1964 by John W. Mc Cutcheon, Inc.

Usually the dispersant makes up between 0.5 and 10% by weight of the charge.

Calcium carbonate with a particle size between 0.1 and 120 µm is used as filler.

These particles can have different structural forms. As an example of these fillers, calcium carbonate in the form of oolitic particles can be mentioned in particular.

Usually has 50 percent by weight of the filler used

according to the invention a diameter between 0.5 and 20 µm.

The production of the adhesives according to the invention can be carried out by simply mixing together, while stirring, the various components mentioned above with water. This can of course be carried out in several steps. It is thus possible, in a first step, to prepare an aqueous dispersion of the polymer that is softened or not, possibly in the presence of a dispersant, and then introduce the calcium carbonate. You can also start by dispersing the filler.

This embodiment can - and this constitutes one of the advantages of the mixtures according to the invention - be carried out at room temperature,

but the mixture can also be prepared at a much higher temperature, e.g. at 60 - 80°C.

In one embodiment of the invention, the water resistance of the obtained joints is improved by further introducing a thermo-curable resin into the mixtures.

In this particular embodiment, between 0.1 and

15% by weight, based on the total weight of dry matter in the dispersion, of a precondensate formed by reacting formaldehyde with a compound selected from the group consisting of phenol, urea, N,N-ethylene urea, dicyandiamide and aminotriazine0

A precondensate is a product with a slightly increased molecular weight (usually between 300 and 2000) which has physical and chemical properties different from the starting compounds, and which are usually soluble or miscible with water and/or organic solvents, as well as being subject to conversion , under the influence of heat and/or a reactive component, to a state where the resin becomes practically insoluble in organic solvents.

The precondensates used in the invention are selected from products that are well known. More specifically, precondensates of phenol/formaldehyde (group A) are usually obtained by reacting 1 to

3 moles of formaldehyde with 1 mole of a phenol.

Examples of phenols include phenol, polyphenols

like for example. resorcin, pyrocatechin, hydroquinone, phloroglucin, alkyl-cycloalkyl- or arylphenols such as e.g. cresols or xylenols, p-tert.vinylphenol, p.cyclohexylphenol, p.phenylphenol. Likewise, bis(p.hydroxyphenyl)methane or bis(p.hydroxyphenyl)-2,2-propane can be mentioned. Mixtures of these phenols can of course be used.

The condensation reaction that leads to these precondensates or "resols" is usually carried out in an alkaline environment.

These precondensates from group A, which are preferably used, are liquids that can be mixed with water. They can thus be easily introduced into the mixtures. Liquids that are not miscible with water can also always be used. In this case, it is advantageous to form de-emulsions of the compounds in the presence of common surface-active agents, for which they are introduced into the mixtures.

The precondensates of formaldehyde with urea, N,N<*->ethylene urea dicyandiamide or an aminotriazine (group B) are usually obtained by condensation of formaldehyde and the nitrogen-containing compound in a weakly acidic or weakly alkaline environment. Usually, the reaction proportions are such that at least 0.6 is used

and a maximum of 2.2 mol formaldehyde per Nl^ group. Usually these precondensates are etherified to varying degrees with an alcohol with 1-6 carbon atoms, such as e.g. methanol, ethanol and butanol.

Among the aminotriazines that can be used to obtain such precondensates, mention may be made of melamine, acetoguanamine, benzoguanamine, formoguanamine, N-(t.butyl)melamines, N-(t.octyl)melamines, in which the t.octyl group has the formula -C( CH3)2 - CH2 - C(CH3)3, ameline, chloroguanamine, hydroxybenzoguanamine, 6-methyl-2,4-diamino-1,3,5-triazine, 2,4,6-trihydrazine-1,3,5- triazine, 2,4,6-triethyl-amino-1,3,5-triazine. Likewise, tris(N,N-dialkyl)melamine can be used, e.g. tris (N,N-dimethylJmelamine.

The precondensates from group B are likewise incorporated into the mixtures in the form of an organic or aqueous solution (if the precondensate is soluble in water). They can likewise be used in the form of powder with a particle size between 10 and 100 µm. This powder can be dispersed directly into the adhesive mixture. The hardening of the precondensates from groups A and B can be increased by heating to between 30 and 60°C for 1 to 4 hours and/or by introducing an acid catalyst, such as e.g. mineral acids (hydrochloric acid, nitric acid, phosphoric acid) or organic acids (formic acid, maleic acid, acetic acid, paratoluenesulfonic acid).

In the case of the phenol/formaldehyde resins, other catalyst types can also be used, such as, for example, the lactones described in German patent document No. 1,065*605. If a catalyst is used, the amount of this usually amounts to between 0.1 and 20% by weight of the precondensate used.

It should be noted that the use of catalysts is not absolutely necessary and especially if the pH of the adhesive mixture is slightly acidic (e.g. if polymers based on vinyl acetate are used which are partially hydrolysed in the presence of the water in the mixture) the curing of the precondensates from group B can be carried out without the addition of catalysts„

It should also be specified that the contact of the adhesive mixture with the grooved layer and the pre-heated overlay causes the temperature in the adhesive mixture to rise and this promotes the rate of hardening of the precondensates.

The methods for producing the adhesive mixtures can be varied. It is thus possible to add the precondensate (liquid or solid) to the dispersion of the polymer and then add water, e.g. in an amount that makes it possible to achieve the desired concentration and possibly catalyst and dispersant, and then to introduce the filler.

You can also mix the dispersion of the polymer in water, the filler and then the precondensate and the catalyst if the solution is not acidic.

The first method is preferably used in the present invention when the catalyst is of an acidic nature, as the introduction of the filler only has an effect in the latter case, as the reaction for hardening the precondensate under the influence of the acid (released from the vinyl polymer and/or added to the mixture) is initiated for this acid is neutralized by the filler. If, therefore, the curing reaction can be activated by means other than the presence of an acid catalyst (e.g. heat), the precondensate can instead be introduced into the mixture which already contains all the other components.

Furthermore, even though the mixtures have the advantage that they can have a high content of solid materials (up to 85% dry matter content), they have all the rheological properties that allow them to be used with normal machines for the production of corrugated board.

The primary application of the usual adhesive dispersions according to the invention is for the production of corrugated cardboard. Other advantages are that the dispersions according to the invention do not have an abrasive effect on the machine rollers, that they adhere very quickly and ensure great strength in the joined parts. The mixtures can be used for other purposes, such as e.g. gluing together paper, wood and leather. The modified mixtures also represent a particularly high water resistance, which makes them very advantageous for use when gluing parts that are exposed to water in a liquid state or steam. This property is particularly beneficial when producing corrugated cardboard that is to be stored in wardrobes.

The following examples describe the invention.

EXAMPLE 1

What is to be produced is a single-sided corrugated cardboard sheet, according to general principles for industrial machines for the production of corrugated cardboard. Trial conditions are as follows:

- production speed: 100 m/min.

- paper width: 130 mm

- theoretical linear pressure on the knurled rollers (achieved with

the rifles): 50 kg/cm.

- linear pressure in the press (applying the cover layer over the grooved layer): 35 kg/cm - device for applying glue with a glue container, a cylinder for applying glue and a cylinder that regulates the thickness of the glue layer to between 0.20 and 0, 25mm,

- the rifles have a distance of 8.6 mm, a height of 4.5 mm. The

is 116 rifles per m in the finished cardboard,

The paper used for the formation of riffles is a paper with a high content of semi-chemical pulp and with a basis weight of 112 g/m 2. The paper for the cover layer is a kraft paper with a basis weight of 150 g/m 2.

The adhesive mixture used in this experiment is an aqueous dispersion containing 30 parts of a homopolymer of vinyl acetate, in the form of particles with an average size between 1

and 2 µm, and softened with dibutyl phthalate (25% by weight in relation to the weight of the polymer), 70 parts calcium carbonate in the form of particles of oolitic form, and average size between 1 and 40 µm (50% of the particles have a diameter between 1 and 3 pm, 0.7 parts sodium hexametaphosphate, the amount of water used in the dispersion is such that the dry matter content amounts to 58%.

The viscosity, according to Stein Hall, of the dispersion is 52 s at 25°C.

The fluted layer of the paper is moistened to approximately 8% by means of water vapor (pressure 2.5 bar).

The fluted cylinders are heated to approximately 180°C.

The adhesive dispersion is applied to the fluted layer at a temperature of 30°C, the paper coming from the fluted cylinders being at a temperature of approximately 80°C.

The adhesiveness and adhesion occur respectively. after 0.1 and 2 sec.

Below are the results of various attempts that were made

applied to the manufactured cardboard (temperature 20°C, relative humidity 60%).

EXAMPLE 2

3 dispersions are produced:

A: - 30 parts of the homopolymer from example 1

- 0.7 parts sodium hexametaphosphate

- 70 parts calcium carbonate (rhombedric structure with particle diameter between 1.7 and 8 pm - 50% by weight has a diameter of approximately 2.5 μm).

- water so that the dry matter content amounts to 63.2%

B: - 30 parts of the homopolymer from example 1

- 70 parts calcium carbonate from dispersion A

- 0.7 parts sodium hexametaphosphate

-0.7 parts polyvinyl alcohol (viscosity at 20°C of an aqueous 4% solution: 4 centipoise, average ester number: 20).

- water so that the dry matter content amounts to 61.2%.

C: - 30 parts of a copolymer of styrene/butadiene with 60% by weight of styrene, in the form of particles with an average diameter between 0.1 and 2 µm

- 0.7 parts sodium hexametaphosphate

- 70 parts calcium carbonate from mixture A

- water so that the dry matter content amounts to 75%

The same equipment as in example 1 is used. The working conditions were as follows: - theoretical linear pressure on the rifles and in the press:

45 kg/cm

- production speed: 100 or 150 m/min.

The above dispersions were used at approx. 26°C.

The manufactured cardboard had the following properties:

EXAMPLE 3

The water resistance test carried out in this example aims to measure the resistance of an adhesive joint (a corrugated layer of paper and a cover layer of paper) which is immersed in water and loaded with a weight on the corrugated layer of paper perpendicularly on the adhesive film. (This text has norm NFQ

03 042).

The test conditions are as follows:

- the corrugated layer of paper is a paper with a high content of semi-chemical pulp, with a basis weight equal to 125 g/m 2. - the cover layer paper is kraft paper with a basis weight of 150 g/cm 2.

These papers are placed for 48 hours in a room with the following conditions: 23°C - 1°C, relative humidity 50% in 2% for the joining.

On a format of a fluted layer of paper (100 x 40 mm), an adhesive film with a thickness of 0.5 mm and a width of 20 mm is applied in relation to the width and perpendicular to the fibers of the paper.

After 0.5 sec. the cover layer paper (5 x 80 mm) is applied with a pressure of 50 g/cm 2. The rough surface of the cover layer paper comes into contact with the adhesive joint, the fibers in the cover layer paper are parallel to the fibers in the corrugated paper. The pressure (50 g/cm 2 ) is maintained for 30 sec. The surface area of the formed adhesive joint is 1 cm 2.

The samples, which consist of glued together layers of corrugated paper and cover layer paper, are kept together for 48 hours in a room with the following conditions: 23°C t 1°C, relative humidity 50% - 2%.

The test pieces are then suspended from the cover layer paper vertically down

in a cylindrical container filled with distilled water at 20°C for 3°C, then a weight of 200 g is attached to the underside of the fluted paper, the distance separating this weight from the lower part of the glue plane being 30 mm. The glue plane is completely submerged in water.

The test pieces are checked visually every hour.

The wet strength of the adhesive joint is expressed as the duration i

hours, i.e. the time that elapses from the beginning of the examination to the moment when a break in the glue plane is observed.

In a mixing device, introduce:

- 60 g of a dispersion of softened polyvinyl acetate

- 0.8 g of hexamethoxymethylmelamine

- 0.08 g of formic acid

The polyvinyl acetate is a homopolymer in the form of particles with a size between 1 and 2 µm. The dispersion contains 30 g of water, 24 g of polymer and 6 g of dibutyl phthalate.

The mixture is stirred for 1 hour and. water is then added in an amount such that the dry matter content of the mixture after the addition of 0.7 g of sodium hexamate phosphate and 70 g of calcium carbonate in the form of oolitic particles amounts to 58% with an average size between 1 and 40 ) xm, (50% of the particles have a diameter between 1 and 3 µm).

With this mixture, 10 joinings are carried out under the above conditions.

It is found that for three joints the wet strength in the joint was respectively 12 hours, one day and l*s day, while for the seven other adhesive joints the wet strengths were more than 5 days.

Claims (4)

1. Aqueous adhesive dispersion, particularly suitable for the production of corrugated cardboard, with a dry matter content of synthetic polymers or copolymers with a particle size between 0.05 and 10 µm, an inorganic filler and optionally a hardenable precondensate of formaldehyde and phenol or an amino-plastic former and optionally a catalyst for curing the precondensate, as well as optionally a dispersant and/or a plasticizer, characterized in that the dry matter comprises: a) 10 to 90 parts by weight of one or more homopolymers of vinyl acetate or styrene, copolymers of vinyl acetate with at least one monomer having at least one ethylenically unsaturated bond, or copolymers of styrene with at least one monomer having two ethylenically unsaturated bonds, and b) 90 to 10 parts by weight of calcium carbonate with particle size between 0.1 and 120 Jim, as the total dry matter content in the dispersion constitutes 50 - 85 percent by weight of the dispersion, and the precondensate, when there is present, constitutes 0.1 - 15 percent by weight in relation to the total weight of dry matter, and includes a reaction product of a phenol, urea, N;N'-ethylene urea, dicyandiamide or aminotriazine. 2. KLebemiddel dispersion as specified in claim 1, characterized in that it contains 0.5 to 10 parts by weight of dispersant, calculated on the weight of the particulate calcium carbonate. 3. KLebemiddel dispersion as stated in claim 1, characterized in that the polymer has added 5 to 50 percent by weight of plasticizer, calculated on the weight of the particulate polymer or copolymer. 4. Chemical dispersion as stated in claim 1, characterized in that it contains a precondensate formed by reaction of formaldehyde with melamine and subsequent etherification with methanol.