WO1998008910A1 - Glue containing lecithine - Google Patents

Abstract

The invention relates to a glue containing lecithine to be applied on one or both faces of the substrates to be glued. For producing same, an aqueous dispersion of a base glue of great initial adhesive power is mixed with about 30 wt % of lecithine in relation to the solid material. The glueing process consists in wetting the substrate surfaces before superimposing them, and then pressing same one against the other during at least 0.1 sec with a strength of at least 0.1 N/cm<2>. The inventive glue is particularly useful in the printing business. The reader can readily loosen the glued cards, envelopes or pamphlets despite the strong adherence given to them during the manufacturing process.

Description

Adhesive containing lecithin

The invention relates to a lecithin-containing adhesive for application to one or both of two substrate surfaces to be bonded. The invention further relates to a method for connecting two substrate surfaces, at least one of which is water-permeable, to the adhesive and to the use of such an adhesive.

JP, A 53072061 describes a lecithin-containing adhesive with an organic solvent for joining polyethylene films. The adhesive contains 100 parts of chlorinated or cyclized rubber and less than 100 parts of lecithin. This mixture is intended to optimize the adhesion between polyethylene films. For example, two polyethylene films are bonded together by, after applying a mixture of 100 parts of cyclized rubber, 40 parts of lecithin, 60 parts of a fatty acid wax, 14 parts of a polyethylene wax, 8 parts

Dimetylpolysiloxan and 650 parts of toluene, the organic

2 solvents, while 3 see at 200 ° are compressed with about 10 kg / cm. The peel strength is 0.1 kg / cm 2 compared to 0.23 kg / cm 2 with a similar adhesive without lecithin.

JP, A 54002285 describes a further lecithin-containing adhesive composition with an organic solvent. The adhesive comprises a cellulose derivative dissolved in an organic solvent and a phosphatide and at least one substance from the group consisting of deethylsiloxane, low molecular weight polyethylene, inorganic filler and pigment. This adhesive allows substrates to be easily detached, for example 12 parts of ethyl cellulose, 2 parts of lecithin, 1 part of dimethylsiloxane, 1 part of low molecular weight polyethylene, 60 parts of PhMe and 24 parts of EtOAc were stirred at a viscosity of 1 P for 20 min. The lecithin-containing adhesive with organic solvent is applied to a paper web, which is used, for example, for the production of milk cartons, dried at 50 ° and pressed at 220 ° and 5 kg / cm2 for 10 seconds. The peel force is 0.15 kg / 15 mm, compared to 0.25 kg / 15 mm when using aetylene cellulose as an adhesive.

US, A 4634727 describes the pressing of chipboard and the like with lecithin as an integrated lubricant. In a polyvinyl acetate adhesive, lecithin is intended to prevent chipboard or similar products from sticking less to their molded panels during their manufacture. Lecithin is preferably added in an amount of 0.5 to 3.0% by weight. Aqueous polymer dispersions are prepared, for example, by polymerizing an onomeric mixture of vinyl acetate and copolymers of vinyl acetate with at least one type of copolymerizable monomers such as ethylene, acrylic acid and its esters, metacrylic acid and its esters, 2-hydroxyethyl acrylate, etc.

HU, A 34231 discloses self-adhesive components based on acrylic ester and vinyl acetate polymers. Preferably 0.3 to 15% by weight of lecithin are applied to various carriers and covered with a peelable self-adhesive film. Numerous details are given for two variants, an aqueous solvent is neither mentioned nor hinted at.

The above documents show a reduced adhesive strength or peel strength of adhesives due to the addition of lecithin. These and other known fugitive adhesives show a constant but low initial adhesion immediately after pressing two substrate surfaces together, which at a later point in time allow problem-free detachment or peeling of a substrate. Thereby there is usually an adhesion break, the adhesive is also detached from the substrate surface. With the same adhesive, the force required for this essentially depends on the nature of the substrate surfaces.

The present invention has for its object to provide an adhesive of the type mentioned, which allows the connection of two substrate surfaces with a high enough initial adhesion for all processing and a later easy, surface-independent separation of the two substrate surfaces, complete for ecological and workplace hygiene reasons organic solvents should be avoided.

With regard to the adhesive, the object is achieved according to the invention in that an aqueous dispersion of a base adhesive with high initial adhesion contains at least about 30% by weight of mixed in lecithin, based on the solids content. Special and further developing embodiments of the adhesive are the subject of dependent patent claims.

Lecithin belongs to the group of phospholipids, in which phosphoric acid is esterified on the one hand with choline and on the other hand with glycerol. If the two free hydroxyl groups of the basic glycerol are esterified with long-chain fatty acids, lecithins (phosphatidylcholines) of the general formula according to FIG. 1 are obtained.

The α configuration shown in FIG. 1 predominantly or almost exclusively occurs in nature. In the β configuration, which is not considered further here, the secondary (middle) hydroxyl group is esterified with the phosphoric acid choline residue.

The fatty acid residues denoted by R 'and R "result in a large number of different lecithins, which in the case of extraction plants are always mixtures.

Soybean lecithins, the most important vegetable raw material before rape and sunflowers, contain, for example, residues R ', R "of palmitic acid, stearic acid, palmitoleic acid, oleic acid, linoleic acid and linolenic acid. Normally, the primary hydroxyl group with a saturated fatty acid is the secondary hydroxyl group (the middle one ) the glycerol is esterified with an unsaturated fatty acid The plant-based lecithins also contain structurally related additives, in particular cephalins.

Lecithins are a hygroscopic, waxy mass, which in the case of lecithins obtained from plants soon takes on a brownish-yellow color in the air. The decomposition temperature is around 200 ° C. Lecithins are easily soluble in ether and often also in alcohol. Lecithins are insoluble in water, but can be dispersed in them.

Lecithins are primarily known as emulsifiers, mainly in the food industry. Lecithins are also used as defoamers or preservatives.

For the production of the aqueous dispersion adhesive according to the invention, based on the solids content, preferably 35 to 80% by weight, in particular 40 to 70% by weight, lecithin is mixed into a base adhesive. With smaller batches of lecithin, the characteristic effects according to the present invention do not occur or only inadequately.

Lecithin is mixed into an aqueous dispersion adhesive in a manner known per se, in this sense it works

Lecithin is not the actual adhesion promoter. Rather, the main effect of lecithin is after to reduce the cohesion of the adhesive applied between two substrates considerably in a relatively short time. When a substrate is peeled off or peeled off, as a rule 0.5 to 2 hours after gluing, the adhesive force (adhesive layer - substrate surface) does not usually result in an adhesion break, but rather a cohesive break, in other words the adhesive layer becomes inherent so separated that parts of it remain on both substrate surfaces. This has the advantage that there is always a separation that is only dependent on the applied adhesive. This is not the case in the event of an adhesion break, where at least one substrate surface plays a decisive role. According to the present invention, however, an adhesion breakage can also occur if the adhesive layer adheres only slightly to a substrate surface.

Soybean lecithins are preferably bleached because of the discoloration, for example by adding about 30% H-0 and then stirring at about 60 ° C. for about 5 hours. The substrate surfaces would be unsightly after using a non-bleached lecithin after a cohesive break.

Lecithin as a white mass which cannot be discolored by light can also be prepared by synthetic processes known to the person skilled in the art. Synthetic lecithin, like that obtained from plants, is available on the market.

Unless finished commercial products are used, the usual additives are expediently mixed in with the base adhesive, in addition to lecithin, for example 0.1 to 2% by weight of preservative, 0.2 ^" to 1% by weight of defoamer and / or 0, 5 to 5 wt .-% compatibility agent, the weight percent as always based on the solids content.

Suitable lecithin-free base adhesives, which

2 tial adhesion of preferably at least 1 N / cm, in particular 2 of which have at least 3 N / cm are, for example, from EP, AI

0470928 and 0624634, to which express reference is made, also with regard to the method. For example, an aqueous base adhesive dispersion can consist of a first dispersion of an acrylic ester copolymer, rubber-containing or not, and a second dispersion of a chloroprene polymerate, the usual auxiliaries or additives also being present in the small amounts indicated. The addition of boric acid is particularly favorable. Basic adhesives are among others manufactured and sold by the patent owner, Alfa Klebstoffe AG, CH-8454 Buchberg, under the SIMALFA brand name.

Individual main components of SIMALFA are also suitable as lecithin-free basic adhesives. Both dispersions of acrylic acid ester copolymers and of chloroprene polymerizates give good results with a lecithin content according to the invention, in particular also with the customary auxiliaries. Instead of synthetic, natural latex can also be used as the basic adhesive.

Basically, not only the above-mentioned, but all adhesive raw materials suitable for the manufacture of adhesives are suitable as basic adhesives.

With regard to the present invention, it is also of particular importance that the essential properties of the lecithin-free base adhesive are retained when substantial amounts of lecithin are added. This applies, for example, to water resistance, paint adhesion and, in the case of thermoplastics, to heat sealability. If an adhesive layer is hot-sealed after reaching the cohesive break area, it loses cohesion during the liquefaction, which in practice lasts a few seconds at most, and regains the same cohesion and adhesive force immediately after hardening, ie remains in the area of the cohesive break. The addition of lecithin only works a gradual decrease in the maximum value of cohesion.

With regard to the method, the object is achieved according to the invention in that the aqueous adhesive dispersion is applied to at least one of the substrate surfaces to be bonded, the substrate surfaces are placed wet on top of one another and are

2 rend at least about 0.1 see with at least about 0.1 N / cm. At least one of the substrate surfaces is porous, so it is permeable to water or absorbent.

Thin layers of adhesive are applied in the range of at least a few grams per m 2, for example 2 to 50 g / m 2. An adhesive strip which is at least about 2 mm, in particular 10 to 15 mm wide, is preferably applied to large substrate areas, this strip being continuous or interrupted. For ecological and workplace hygiene considerations, the aqueous dispersions according to the invention are always advantageous over adhesives with organic solvents used according to the prior art.

It has been found that the faster the dispersion adhesive dries, the greater the adhesive force, the adhesion. This in turn depends on the porosity of the substrate surface (s).

An increase in the adhesive force can also be achieved if hot activation takes place. If the adhesive is warmed up a little, the cohesion increases.

An aqueous adhesive dispersion composed and applied according to the invention always leads to a connection of two substrate surfaces with high initial adhesion, initially constant or increasing and after a short time decreasing cohesion into the area of the cohesive break. The initial adhesive force acts immediately after laying on and pressing on, the cohesion and the adhesive force (adhesion) reach a maximum value after a short time, usually after a few minutes. Then the cohesion decreases to a maximum of approximately 50%, in particular to a maximum of approximately 30% of the maximum value and remains approximately constant, the range of a low cohesion break during peeling is reached. If the adhesion is once less than the cohesion, an adhesion break occurs during peeling, the adhesive layer is retained and as such is detached from the relevant substrate surface.

The person skilled in the art can easily determine the relevant characteristic values for each adhesive, which can be controlled with a fixed adhesive by the choice of the substrate surfaces and any hot activation.

Coated substrate surfaces are, for example, normal paper, coated paper, printed paper, also poorly anchored lines and printing inks, and cardboard. Even difficult substrates such as metal foils, PVC and the like can be coated with an appropriate adhesive dispersion containing lecithin.

After peeling off with cohesive breakage, the adhesive residues remain on the surfaces. As they are transparent, they usually do not interfere any further, otherwise an attempt is made to break the adhesive.

The uses of an adhesive containing lecithin are extremely diverse, for example:

In magazines cards, envelopes or entire brochures are stuck in for advertising purposes, which can be used for printing and

Wrinkles must have a good initial adhesive force, but afterwards, if possible, remove them without tearing the paper are. With the adhesive according to the invention, inserts can also be applied to printed and / or illustrated pages without problems, the peeling with a cohesive break in the case of greatly reduced cohesion prevents the ink from peeling off or even a paper break. Inserts pre-coated over the entire surface with lecithin-containing, thermoplastic adhesive can be glued in by means of punctiform or strip-shaped heat sealing; the greatly reduced cohesion for a cohesive fracture when being removed remains. The adhesive residues left on the paper are transparent and do not disturb the reader any further.

When making paper rolls, the beginning is glued onto a cardboard tube, the end onto the roll. An increased initial liability for the beginning and the end is advantageous in terms of production technology, as is easier peeling during use, for example in the case of a toilet roll.

Labels of all kinds can be applied not only to a carrier with a silicone base, but also to paper for storage on a roller conveyor and the like. Then it is particularly important to apply it with an increased initial adhesive force and peel it off by breaking the cohesion with greatly reduced cohesion. A label loss at the beginning and end is always prevented.

Items offered in the multipack are usually "bundled" with a shrinkable wrapping film with a thickness of 60 to 70 μm. According to the invention, a smaller film thickness of ~ 25 to 30 μm with an adhesive application of

2 2 g / m used. The wrapping can be complete or done using broadband technology. example 1

A heat-sealable polyethylene dispersion is applied in the form of a 10 mm wide strip, namely the SIMALCO 5512 adhesive from Alfa Klebstoffe AG, CH-8454 Buchberg,

2 with about 20 g adhesive / m. This adhesive, a water-based, fast-setting synthetic resin adhesive with about 35% by weight lecithin, based on the solid, serves e.g. the mechanical fixation of cardboard and label roll ends. It can also be applied to a substrate surface with poorly anchored lines and printing inks. The application takes place with roller application or electronically controlled nozzle application. Both applications have very good machine running properties.

SIMALCO 5512 has the following essential properties:

- Composition: Plasticizer-free copolymer dispersion - Solids content: approx. 43%

- pH: about 8

- Viscosity according to DIN53019 with a shear rate gradient of 100s ^"1 : about 370 mPas - Storage stability: at + 5 ^β C to + 40" C in

Original containers at least 6 months

- Cleaning: can be thinned and washed with

Water - mandatory labeling: no dangerous good

2 shows the time in minutes since the application of the adhesive and the joining of the substrate surfaces on the abscissa, and the peel values of a 15 mm wide adhesive strip in grams corresponding to the cohesion are plotted on the ordinate. The first material crack limit represented by curve 1 runs parallel to the abscissa. If the peel value of the applied adhesive is above this straight line, paper peeling is possible when a substrate surface is peeled off. The time-independent peel value of 50 g according to FIG. 1 is characteristic of weak paper, for example newsprint.

If instead of ordinary newsprint paper a strong paper is used, such as is used in the packaging industry, the material tear-out limit is significantly higher, according to curve 2 at 90 g. Of course, this straight line again runs parallel to the abscissa, and the material tear-out limit for strong paper is also independent of time.

If SIMALCO 5512 is applied to coated paper, an initial adhesion with a peel value of approximately 18 g is achieved immediately after joining and pressing. The cohesion increases to a peel value of about 65 g within the first 5 min and then falls to a peel value of less than 30 g within the next 30 min. In the further course of time, the cohesion drops only slightly. This curve is represented by curve 3. When the lecithin-containing adhesive is applied to strong paper, there is never a tear-off of the material. When applying to newsprint, it is hardly possible to tear out paper after the first 20 minutes, previously likely. When peeling off there is a break in the cohesion below the tear-out limit, the adhesive film is separated. This course of the peeling value over time is advantageous in every respect, high during industrial processing, low during peeling.

When the adhesive layer containing lecithin is applied to richly printed paper, the initial adhesive force is lower with a peel value of about 10 g. In the first 5 min, the cohesion increases to about 45 g and drops to a value of less than 10 g after 30 min. The peel value according to curve 4 remains approximately constant over the next 30 minutes. After half an hour, richly printed paper has such a low peel value that the cohesive break not only remains without the slightest damage to the paper, but also has no effect on the printing ink.

Thanks to its greater porosity, the lecithin-containing adhesive sets much faster on unprinted, coated paper than on saturated printed paper, which is why a higher initial adhesion and a higher maximum cohesion and adhesive force (adhesion) are achieved. 2, the possible paper tear-out limit is not reached even with newsprint.

2 In the range from 2 to 40 g adhesive / m, the curves according to Fig. 2 do not tend to change.

When using other adhesives with a higher initial adhesive force and greater maximum adhesion, the material tear-out limit for strong paper can of course also be reached.

The adhesive used is matched to the respective conditions using expert knowledge. The parameters initial adhesion, maximum cohesion, time to reach maximum cohesion, time to reach cohesion break and peel value in the area of cohesion break are the main parameters to be taken into account.

If a natural or artificial latex dispersion with at least about 50% by weight of lecithin, based on the solids content, is applied, curve 5 results. This runs horizontally for about 10 minutes at a value of about 38 g, the cohesion initially corresponds to about the initial tung. Then the cohesion first decreases more strongly, then weakly, and after 60 minutes reaches an approximately constant peel value of about 13 g, as always in relation to a 15 mm wide adhesive strip.

Trends of type 3, 4 or 5 according to FIG. 2 tend to be approximately the same for other adhesives with at least about 30% by weight lecithin. After the application of the adhesive layer and the joining and pressing together of the substrate surfaces, an initial adhesion arises, which increases to a maximum value for the cohesion within a few minutes or remains constant for the time being. The cohesion decreases more strongly in the course of the following minutes, weaker after 20 to 30 minutes to a minimum value which is usually reached after 0.5 to 2 hours. This allows easy peeling under a cohesive break in the adhesive layer.

The adhesive force (adhesion) is always greater than the cohesion, at least in the cohesive fracture area, otherwise the adhesive layer would delaminate from the substrate surface instead of being separated.

Example 2

The SIMALCO 5502 adhesive, likewise a lecithin-containing synthetic resin adhesive according to the present invention, also contains, based on the solids content, more than about 30% by weight of lecithin and sets very quickly. It is particularly suitable for difficult substrates such as metal foils, PVC, etc. The plasticizer-free copolymer dispersion contains about 50% solids, has a pH of about 6 and a viscosity of about 445 mPas. Example 3

Other adhesives from Alfa Klebstoffe AG, CH-8454 Buchberg, are suitable as a basis for adding lecithin in the scope of the invention, for example ALFA D101, D253, D259, D312, D2106, D3523, D4034 and D4572. These basic adhesives have individual specific properties, these are not changed by the addition of lecithin, in particular sealable adhesives remain sealable even after the addition of lecithin and after reaching the area of the cohesive break.

Example 4

The following lecithin-containing aqueous dispersion adhesives according to the invention met all requirements with regard to the initial adhesion and the time profile of the peel values (see FIG. 2), the% by weight always referring to the solids content:

a) 43% by weight of the aqueous acrylic resin copolymer Acronal A 603 (BASF), 48% by weight lecithin, the rest of the usual additives

b) 25% by weight of Acronal A 603, 23% by weight of Poligen MV 250 (BASF), an aqueous acrylate-styrene dispersion crosslinked by metal ions, 50% by weight of lecithin, the rest of the usual additives

c) 33% by weight of an aqueous colloidal dispersion of a polymer of 2-chlorobutadiene - (1,3), namely the chloroprene DISI ^ RCOLL C84 (BAYER) as synthetic latex, 66% by weight lecithin, the rest of the usual additives , pH 9-10

d) 48% by weight of natural latex, 51% by weight of lecithin, the rest of the usual additives e) 33% by weight of natural latex, 65% by weight of bleached lecithin, the rest of the usual additives

f) 1 to 4 wt .-%, in particular about 2 wt .-%, Acronal A 603 or A 310 S (BASF), 31 wt .-% chloroprene DISPERCOLL C84

(BAYER), 64% by weight lecithin, balance usual additives. The

Addition of the acrylic resin copolymer serves to regulate the adhesion.

Variants c) to f) have the additional advantage that a film-shaped substrate can be removed elastically and always continuously. 2, the peel values of the adhesives a) and b) run essentially according to curves 3 or 4, the peel values of the adhesives c) to f) according to curve 5.

Example 5

With the Acronal 205 dispersion adhesive, also an aqueous acrylic resin copolymer, with a lecithin content of at least 30% by weight with respect to the solids content, sticky residues are obtained after peeling off a substrate by cohesive fracture, which residues again after pressing on a clean substrate surface tie. In the tests with other adhesives, the residues after the cohesive break are blunt, a new adhesive connection with the residues is not possible. This is e.g. important for labels applied on a roll, removable and applied for the labeling of objects.

Claims

claims 1. lecithin-containing adhesive for application to one or both of two substrate surfaces to be bonded, characterized in that an aqueous dispersion of a base adhesive with high initial adhesion, at least about 30% by weight of admixed lecithin, based on the solids content. 2. Adhesive according to claim 1, characterized in that it contains, based on the solids content, 35 to 80% by weight, preferably 40 to 70% by weight, lecithin. 3. Adhesive according to claim 1 or 2, characterized in that it contains previously bleached or synthetic lecithin. 4. Adhesive according to one of claims 1 to 3, characterized in that the lecithins contain as fatty acid residues palmitic acid, stearic acid, palmitoleic acid, oleic acid, linoleic acid and / or linolenic acid, a saturated fatty acid preferably with the primary, an unsaturated fatty acid preferably with the secondary Hydroxyl group of the glycerol esterified. 5. Adhesive according to one of claims 1 to 4, characterized in that the lecithin-free base adhesive has an initial adhesion of at least 1 N / cm 2, preferably 2 wise of at least 3 N / cm, this initial adhesion remains essentially unchanged due to the addition of lecithin. 6. Adhesive according to one of claims 1 to 5, characterized indicates that the lecithin-free base adhesive dispersion contains at least one acrylic acid ester copolymer and / or one chloroprene polymer as main component (s). 7. Adhesive according to one of claims 1 to 6, characterized in that the lecithin-free base adhesive dispersion contains natural or synthetic latex as the main component or as one of the main components. 8. A method for gluing two substrate surfaces, at least one of which is water-permeable, with an adhesive according to one of claims 1 to 7, characterized in that the aqueous adhesive dispersion is applied to at least one of the substrate surfaces to be bonded, the substrate surfaces are placed wet on top of one another and pressed on for at least about 0.1 seconds with at least about 0.1 N / cm. 9. The method according to claim 8, characterized in that a preferably at least about 2 mm, in particular 10 to 15 mm wide, continuous or interrupted adhesive strips is applied to large substrate areas. 10. Use of the adhesive according to one of claims 1 to 6 in the printing industry for cards, envelopes or brochures glued in easily detachable by the reader.