WO1998055559A1

WO1998055559A1 - Method for sticking substrate surfaces elastically

Info

Publication number: WO1998055559A1
Application number: PCT/CH1998/000232
Authority: WO
Inventors: Emil Simmler; Thomas Simmler
Original assignee: Alfa Klebstoffe Ag
Priority date: 1997-06-03
Filing date: 1998-06-03
Publication date: 1998-12-10
Also published as: AU7423098A; DE19880759D2

Abstract

The invention relates to a method for sticking substrate surfaces elastically with an aqueous dispersion adhesive. Said dispersion adhesive comprises a dispersion with a polyurethane elastomer base as a first constituent and a dispersion with an acrylic ester copolymer and/or a vinyl acetate and ethylene copolymer base as a second constituent. A thin layer of the dispersion adhesive is applied to at least one of the substrate surfaces for sticking. In the case of two non-porous substrate surfaces, the adhesive is applied in streaks or thin spots. The dispersion adhesive is partially dephlegmated with a brief thermal shock, before the substrate surfaces are laid on top of each other and, usually, briefly pressed together.

Description

Process for elastic bonding of substrate surfaces

The invention relates to a method for the elastic bonding of two substrate surfaces with an aqueous dispersion adhesive and an advantageous application.

If two substrate surfaces are coated with an adhesive and placed on top of each other after the adhesive has dried, this is called a contact adhesive. With conventional adhesives, this can only take effect when the solvent or the water has evaporated. If only one of the two substrate surfaces to be connected is coated with an adhesive and the other, untreated substrate surface is placed on and pressed on after the solvent or water has evaporated, it is a single-sided adhesive. The terms contact and single-sided adhesive are retained even when the substrate surfaces are stacked with wet adhesive.

Adhesives dissolved in volatile organic solvents can be processed quickly. However, this advantage is largely or largely eliminated by a number of disadvantages. The organic solvents escaping during spraying and drying represent a significant labor-economic loss. Furthermore, the volatilizing solvents are flammable, harmful to health and / or polluting. Despite specially built systems and extensive precautions to avoid uncontrolled escape of organic solvents, the legislature has intervened in numerous industrial countries and the use of organic solvents, if this has not already been done, will be largely prohibited in the near or medium future or with high taxes occupied, e.g. with VOC shelves (VOC: Volatile Organic Compounds). EP, AI 0470928 and 0624634 show aqueous dispersions and methods for the elastic bonding of two substrate surfaces, which allow the use of aqueous dispersions as contact or single-sided adhesives. Surprisingly, these aqueous dispersions show a high initial adhesion when the two substrate surfaces are placed on top of one another with wet adhesive and pressed briefly. The adhesive dispersions are pressure-sensitive; without water being released, a setting process is initiated immediately when pressed on. According to the first-mentioned EP, AI 0470928, a first dispersion with an acrylic acid ester copolymer and a colloidal second dispersion of a chloroprene polymer is applied to at least one of the substrate surfaces after prior or simultaneous mixing. The substrate surfaces to be bonded with the wet adhesive dispersions are placed on top of one another and pressed on. EP, AI 0624634 describes an adhesive for foams and other materials with a porous surface, a sprayable dispersion based on an acrylic ester copolymer and a colloidal chloroprene polymer, which contains boric acid as a characteristic feature.

WO 94/05738 discloses the use of aqueous dispersions made from a polymeric, film-forming thermoplastic and polyurethane for bookbinding purposes, including the addition of latex to the dispersion. The dispersion is dried off after careful application. The evaporation of the volatile components can be accelerated with heating devices, heating lamps, blowers and the like, but in normal cases the normal drying speed is sufficient. The aqueous dispersion can also be used as a primer. The volatile components of the dispersion have evaporated before further processing of bound paper stacks. From WO 94/05738, no reference to the bonding of two substrate surfaces with high initial adhesion can be seen or derived; a dry, melted adhesive layer, also called heat seal.

The present invention has for its object to provide a method for the elastic bonding of two substrate surfaces with a dispersion adhesive, which further improves and / or simplifies the initial adhesive force of wet superimposed substrate surfaces, ensures a particularly high final adhesive force with respect to cohesion and adhesion with high elasticity and also allows a long, practical processing time after applying the dispersion without losing the economic and ecological advantages of less efficient processes with aqueous dispersion adhesives.

The object is achieved according to the invention in that a dispersion adhesive, consisting of a first component based on a polyurethane elastomer and a second component based on an acrylic ester copolymer and / or a copolymer of vinyl acetate and ethylene, as a thin layer on at least one of the applied substrate surfaces to be bonded, partially dewatered with a short burst of heat and the substrate surfaces to be bonded are placed wet on top of each other. Special and further embodiments of the invention are the subject of dependent claims.

The aqueous dispersion adhesives used can be used as contact or single-sided adhesives. A high initial adhesive force, which is at least comparable to that of solvent-based adhesives, can be achieved in seconds after application. In contrast to WO 94/05738 discussed at the beginning, wet or still moist surfaces are always placed on top of one another.

The initial adhesive force achieved with the method according to the invention is independent of a prior ventilation. With a shorter machine stop, there are no production downtimes, the applied dispersion remains wet or open for a comparatively long time and retains its advantageous properties essentially unchanged until shortly before drying out, for example after 15 to 30 minutes.

The dispersion adhesives used in the process according to the invention are preferably pressure-sensitive. Depending on the dead weight of the substrate to be glued, which is on top when joining, the coagulation or the destabilization of the dispersion adhesive can already be triggered by the dead weight. As a rule, however, there is a short pressing, in particular for 1 to 5 seconds with expedient 0, 2

2 to 1 N / cm, which ensures the necessary shock to trigger coagulation.

A targeted triggering of the coagulation with a high initial adhesive force is essential in practice.

A dispersion adhesive used in the process according to the invention is expediently produced in a mixer of conventional design, the components being added in a predetermined sequence. A completely mixed dispersion can be stored in the absence of air for several months without coagulating.

A dispersion adhesive preferably has a solids content of 40-80% by weight, in particular 55-75% by weight. The rest is essentially water, but in industrial practice it also contains the additives commonly used for dispersion adhesives. Often these are not known to the user, they are not specified by the manufacturer of the adhesive raw materials.

The first and second components are preferably applied in a mixing ratio of the first to the second dispersion of about 1: 1, based on the solids content.

However, this ratio is not critical, the deviation can vary within wide limits, expediently in the range from 90:10 to 10:90, based on the weight ratio of the solids between the first and the second component.

In order to avoid premature initiation of coagulation, the pH of the dispersion adhesive is preferably in the weakly acidic to basic range, in particular in the range from 7 to 9.

The already extremely high initial adhesion of a dispersion adhesive used can optionally be further increased by mixing up to 80% by weight of natural latex and / or synthetic rubber, preferably with a proportion by weight in the range from 20 to 70%, in particular 40, according to a particular embodiment up to 60%, based on the total solids content.

The first component of an aqueous dispersion adhesive used according to the invention and based on a polyurethane elastomer is essentially composed of polyisocyanates, dihydroxy compounds and chain extenders. It is also advantageous to add a crosslinker which contains at least two groups which are reactive toward isocyanate.

Although polyurethanes and their properties, which are also used as adhesives, have long been known and have repeatedly been the subject of numerous publications, the following is carried out with regard to the individual polyurethane components:

- Aliphatic, cycloaliphatic and aromatic diisocyanates are particularly suitable as polyisocyanates. These have the general formula X (NC0) ". Component X denotes an aliphatic hydrocarbon residue with expediently 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon residue with expedient 6 to 15 atoms or an aromatic hydrocarbon residue with expedient 7 to 15 carbon atoms. As specific examples, 1,4- Butane diisocyanate, cyclohexane diisocyanate and 2,6-toluene diisocyanate are listed. Suitable mixtures of diisocyanates are also suitable.

The dihydroxyl compounds preferably have a molecular weight of 400 to 6000 g / mol, in particular polyester diols, reaction products of dihydric alcohols with dibasic carboxylic acids, for example phthalic acid, adipic acid, maleic acid, furaric acid and dimeric fatty acids. Suitable alcohols for polyester diols are, for example, ethylene glycol, propylene glycol - (1,2) and - (1,3), o-hexanediol and polyethylene glycol.

- Chain extenders preferably have a molecular weight below 400 g / mol. These are, for example, compounds with two hydroxyl groups, two primary or secondary amino groups or one hydroxyl and one primary or secondary amino group. Examples here are ethylenediamine, hexamethylenediamine, piperazine, ethanolamine and isopropanolamine. Chain extenders usually also have a crosslinking function.

When specifically used in the context of the present invention, these polyurethanes not only ensure a high initial adhesive force, but also universal uses for polar and non-polar substrates, with good resistance being retained even when exposed to moisture. The production of a polyurethane, which is not the subject of the present invention, is described for example in DE, A 3437918.

The adhesive raw material Luphen D DS 3482 X, an aqueous, specially modified dispersion of a polyester-polyurethane elastomer from the German company BASF, leads to advantageous results. The acrylic ester copolymer used as the first variant of the second component of a dispersion adhesive used according to the invention, also referred to in its entirety as acrylic acid acid copolymer, can also include acrylic ester-styrene copolymers. The adhesive raw material Acronal A 310 S from the already mentioned German company BASF is advantageous, which product is an aqueous dispersion of an acrylic ester copolymer that self-crosslinks at room temperature.

As a second variant for the second component of the dispersion adhesive, the Vinnapas dispersion EP 400 from the German company Wacker has proven to be advantageous. It is a 55% plasticizer-free polymer dispersion of a copolymer of vinyl acetate and ethylene in water.

The two variants, an acrylic ester copolymer on the one hand and a copolymer of vinyl acetate and ethylene on the other hand, can be used individually, but also mixed with the first component, a polyurethane elastomer.

The mixing of additional components into a dispersion adhesive used according to the invention depends on the mixed commercial product (s), which as a rule already contains / contain specially specified additional components, and the desired properties of the dispersion. One or more of the following organic components are e.g. suitable for:

- N-alkylpyrrolidone, for example in the form of N-methyl-2-pyrrolidone, up to 15% by weight, based on the solids content, and / or a substance from the group consisting of N-octyl-2-pyrrolidone and N-dodecyl -2-pyrrolidone, preferably up to 10% by weight in each case, always based on the solids content. N-methyl-2-pyrrolidone can also be mixed with N-octyl-2-pyrrolidone or N-dodecyl-2-pyrrolidone, with unchanged proportions by weight. The former N-methyl-2-pyrrolidone serves as a machine-improving plasticizer, the other two pyrrolidones tend to promote coagulation and wetting.

The addition of sodium lauryl sulfate, preferably in a concentration of 0.1 to 3% by weight, based on the solids content, improves the mechanical properties, in particular the machinability, when applied by spraying.

- With the aim of softening, promoting adhesion, heat resistance and storage stability, dimethyl phthalate or diisobutyl phthalate can also be mixed in as a further component, preferably with up to 20% by weight, again based on the solids content.

- Further optional additional components known to the person skilled in the art are, for example, defoamers (Tego Antifoam 2- 89), emulsifiers (Emulphor OPS 25), dispersion powders for a high solids content (Acronal DS 6200), soft resins (Dertoline 25) and thickeners (Latekoll D 8%) ). A marketable product name is always given in brackets.

- Finally, fine-grained filling materials can also be mixed in, preferably ZnO, MgO and / or color pigments.

The aqueous dispersion adhesive is preferably coated with a

2 specific amount from 2 to 150 g / m, especially from 15

2 to 100 g / m, based on the solids content, applied.

The dispersion adhesive is applied using a method known per se, for example by rolling, brush application or spraying, the latter using a nozzle bar, but also using a spray gun. However, the dispersion adhesive is not sprayed on atomized, but in dripping sprayed on chenform.

The short shock drainage of the applied dispersion adhesive layer is of importance for the invention. However, this shock drainage must never take place more than partially, preferably 10 to 50% by weight of the water, preferably 15 to 25% by weight, based on the total water content, evaporate. Tests have shown that even a small loss of water in the dispersion adhesive layer leads to a steep increase in the initial adhesive force. In this way, standing up and material tension can be absorbed.

If too much water evaporated, the opposite joint surface could only be insufficiently wetted and an unsatisfactory initial adhesive force could be achieved.

With regard to the present invention, it is of particular importance that not only two porous substrates or one porous can be bonded to a non-porous substrate, but also two absolutely non-porous substrates if the adhesive is not applied over the entire surface. In the latter case, the dispersion adhesive is applied as a preferably approximately 15 mm wide strip or corresponding flat dots. The already partially dewatered dispersion adhesive then dries for several days due to the time-delayed water evaporation. The high initial adhesive force leads to a completely sufficient adhesion to all types of substrate surfaces within a very short time.

The components of the dispersion glue used are selected on the basis of the manufacturer's information sheets so that the dispersion glue to be mixed can be specifically aligned to the substrate surfaces to be glued. Further improvements are achieved by adding special additives, for example a metal or a plastic one. Further, for example higher cohesion can be achieved by crosslinking using a polyisocyanate.

The heat surge that leads to partial drainage, called shock drainage, is carried out, for example, with hot air or a gas flame, by using HF (high-frequency alternating currents) or IR radiation (infrared radiation), or with the help of a contact shoe. Depending on the dispersion and throughput speed, the temperature is preferably in the range from 40 to 400 ° C. In practice, the heat is expediently applied for 0.1 to 3 seconds, the adhesive layer preferably being heated to a desired value in the range from 60 to 150 ° C. Both the heat source and the substrate can be complementarily stationary or movable. In the case of film-shaped substrates, the heat is preferably supplied from the rear or the back of the substrate surface covered with the adhesive layer.

The heat capacity of the substrate, e.g. made of paper or cardboard, can store part of the thermal shock and thus have an after-effect. This is the case, for example, in the event of a thermal shock to an envelope.

The use of the method according to the invention is particularly advantageous in bookbinding technology; a much better and also faster perfect binding can be achieved on an automatic binding machine. After the sheets and milling machines have been gathered together, gluing the spine of the book with the dispersion adhesive according to the invention can achieve an hourly output of 3000 pieces per hour, for example from catalogs or brochures, by means of natural drying within 2 to 3 seconds after gluing the spine. With a short burst of heat for about 1 to 2 seconds with significantly higher than natural partial drainage, the same automatic binding machine can achieve an output of up to 10,000 pieces per hour. The flexibility that is particularly important in bookbinding technology remains in spite of high cohesive and adhesive power maintained.

Further specific measures in bookbinding technology can be used in the further development of the dispersion adhesive according to the invention:

- A mixture of 1 to 15% by weight of glycerin and boric acid is added to the dispersion, based on the solids content. This mixture of glycerin and boric acid in a preferred ratio of about 6: 1 is previously heated.

- The solids content of the dispersion adhesive is increased by metering in at least one component already contained or new. Up to about 15% by weight of dispersion powder, based on the solids content, are preferably added.

- A mineral filler is added in the same weight percentage range.

The aim of these measures is to achieve a very high initial adhesive force even when the water release is below about 10%.

Further advantageous applications of the method according to the invention are bag production with plastics and packaging made of paper. In the case of thin and thermally highly conductive materials, the heat shock can also be given from the back.

The main advantages of the invention can be summarized briefly as follows:

- Extremely high and fast initial adhesive force due to a heat shock leading to partial drainage, both on porous or absorbent substrate surfaces, such as cardboard, Paper, wood, leather, as well as with two non-porous substrate surfaces, such as metals or plastics, after just a few seconds.

- No use of organic solvents or solvent components, which pollute the workplace and the environment, and practically pH-neutral.

- High heat resistance, not flammable.

Claims

claims

1. Process for the elastic bonding of substrate surfaces with a dispersion adhesive,

characterized in that

a dispersion adhesive consisting of a first component based on a polyurethane elastomer and a second component based on an acrylic ester copolymer and / or a copolymer of vinyl acetate and ethylene, applied as a thin layer to at least one of the substrate surfaces to be bonded, with a short one Heat shock partially drained and the substrate surfaces to be bonded are placed wet on top of each other.

2. The method according to claim 1, characterized in that the dispersion adhesive is applied with a specific amount of 2-150 g / m 2, in particular 15 - 100 g / m2, based on the solids content.

3. The method according to claim 1 or 2, characterized in that the dispersion adhesive is applied to two non-porous substrate surfaces as strips or as flat dots.

4. The method according to any one of claims 1 to 3, characterized in that the short shock dewatering with hot air, a gas flame, HF, IR radiation or a contact shoe, in particular with an acting temperature of 40-400 ° C, and 10-50 % By weight of the water, preferably 15-25% by weight, based on the total water content, are evaporated.

5. The method according to any one of claims 1 to 4, thereby indicates that the shock drainage takes place during 0.1 - 3 sec, with heating of the adhesive layer to preferably 60 - 150 ° C.

6. The method according to any one of claims 1 to 5, characterized in that the heat is supplied from the rear during the shock drainage of film-shaped substrates.

7. The method according to any one of claims 1 to 6, characterized in that the superimposed substrate surfaces are pressed together briefly, preferably

2 for 1-5 sec with a pressure of 0.2-1 N / cm.

8. The method according to any one of claims 1 to 7, characterized in that a dispersion adhesive with a solids content of 40-80 wt .-% and a pH of preferably 7-9 is used.

9. The method according to any one of claims 1 to 8, characterized in that a dispersion adhesive with up to about 80 wt .-%, preferably 20 - 70 wt .-%, mixed natural latex and / or synthetic rubber, based on the total solids content, is mixed .

10. The method according to any one of claims 1 to 9, characterized in that for bookbinding purposes a dispersion adhesive with an additional mixture of 1-15 wt .-% glycerol and boric acid, based on the solids content, is applied, the ratio glycerol: boric acid preferably is about 6: 1.

11. The method according to any one of claims 1 to 10, characterized in that for bookbinding purposes a dispersion adhesive with additional dispersion powder and / or a filler, preferably up to 15 wt .-%, based on the solids content, is applied.