CZ114489A3 - Process for preparing thixotropic contact acrylic adhesives - Google Patents

Abstract

A process for preparing thixotropic contact acrylic adhesives, formed by a solution of alkyl copolymer and/or aryl acrylate or methacrylate monomers, acryl or methacrylic acids and/or their amides, substituted to nitrogen by alkyl, alkoxyl or methylol groups in a mixture of organic solvents and modified by additives, colours and fillers. Its essence is the subsequent modification of the solution of copolymer by anhydride of bifunctional organic acid, preferably maleic anhydride at 85 to 100 degrees C over 2 to 4 hours.

Description

The invention relates to a process for the production of thixotropic contact acrylate adhesives used for the production and preparation of pressure-sensitive adhesive layers applied to a suitable substrate or directly to the object to be bonded. These adhesives are characterized by the distinctly thixotropic nature of the solution, coupled with high adhesive adhesion to various surfaces, high cohesion, providing mechanical properties of the adhesive, and sufficient elasticity to allow their use on dark, flexible materials.

For the production of self-adhesive materials utilizing the properties of thixotropic acrylate adhesives, the process is generally applied by applying the adhesive solution to the surface of the material (foil, paper, textile substrates) by means of a ruler, skates, slit or application rollers. The use of silicone paper is often used as a removable backing, which is then pressurized by its own durable carrier. Ero technology - such processing properties of the adhesive as thixotropic application behavior, permanent elasticity and tack, relatively high evaporation of the solvents used are important.

However, other properties are more important for the actual application of the finished self-adhesive system, in particular permanent tack and minimal plastic flow.

Originally, natural raw materials, especially raw rubber mixed with rosin or other resinous products, have been used to prepare the self-adhesive layers. The actual preparation of the adhesive consisted of dissolving the adhesive polymer - rubber and other additives in a suitable solvent mixture. The adhesive layers prepared from these solutions, however, had only a transient effect. Due to aging and the associated oxidation, the adhesive layer lost its elasticity and tack, and after some time the system completely disintegrated.

This deficiency has not been overcome by modifying such adhesive layers with synthetic resins or thermoplastic polymers and copolymers. It has also been shown not to be suitable for long-term applications.

The use of acrylate contact adhesives has proven to be sufficiently advantageous, especially since the acrylate copolymers can be suitably combined so that the resulting adhesive layer has a long-lasting and high tack, elasticity, resistance to sunlight and air components.

Low cohesive energy usually results as their basic deficiency, which results in insufficient strength of blinds on vertical surfaces. The pronounced cohesion energy causes the adhesive layer to tend to plastic flow even at normal temperature (cold flow). Depending on the load of the joint in the vertical plane and the thickness of the applied adhesive layer, there is a gradual plastic deformation of the layer in the direction of the applied force and gradually up to its flow and thus slipping of the glued object.

To remove, respectively. at least the reduction of the plastic flow phenomenon is used in essentially two ways. The first is that the polymerization results in the highest molecular weight of the polymer or copolymers. Extremely high molecular weight macromolecules are characterized by high cohesion energy density and reduced tendency to plastic flow. Therefore, the actual polymerization or copolymerization is conducted consciously slowly, at reduced temperatures, in order to favor the growth of the molecule over the initiation of new polymerization centers.

The accompanying phenomenon of the formation of extremely large macromolecules of copolymers is generally a reduction in their solubility in all applicable solvents. The adhesive solution contains a large number of swollen insoluble gels, which degrade the quality of the adhesive layer upon application to the substrate by forming unevenly distributed dot clusters of polymer. Filtering them out of the adhesive solution before application is very difficult and largely impossible, since the swollen polymer particles deform under pressure and penetrate through fine filter materials.

A process for producing these polymers and copolymers that uses cross-linking reactions to increase the size of the macromolecules of the polymer results in similar, but rather intensified, consequences,

i.e., increasing the molecular weight by forming cross-molecular intermolecular bonds. Especially in these cases, the resulting macromolecules are difficult to dissolve in solvents and lose extreme adhesive properties.

The second method used so far is the addition of an adhesive solution of thixotropic agents, such as aliphatic monocarboxylic acids having carbon numbers of 10 or more, their ammonium and metal salts, esters and amides, or oligomers thereof. Such agents include, for example, stearic acid, hydroxystearic acid, fatty acids of natural origin, ammonium, lithium, calcium stearate, glycerin stearate. Rather, their thixotropic effect lies in the formation of hydrogen bonds, which break down even at low tangential stresses. '

Macromolecules of different types are characterized not only by different solubilities in different types of solvents, but also by mutual immiscibility in solutions. Therefore, it usually happens that even a well-mixed glue solution, seemingly homogeneous, has a high viscosity

after two days of standing, it is divided into two phases, since a thermodynamic equilibrium is slowly created between the pole solution; and copolymers and a thixotropic additive solution. The additive itself settles at the bottom of the tank or shipping container as a separate viscous layer and the adhesive must be vigorously mixed to at least partially redistribute the agent in solution. In most cases, however, the two phases cannot be permanently combined again. The actual effect of the additive is thereby severely limited and sometimes even completely eliminated.

In addition, the formation of a new phase, whether swollen excess molecular weight copolymer particles or the separation of the swollen thixotropisizing agent, causes the formation of various coating defects when applying the leuide agent. The adhesive layer is inhomogeneous after drying, the outlet of its dirt} '' and the villi reduce the contact plate at better '!'! and the apparent adhesion of the self-adhesive materials in use.

These disadvantages and shortcomings can be eliminated and the quality of the material crucial ??? ako? ' to increase the process, which is first of all the invention. It is based on a process for the production of thixotropy contact acrylate adhesives comprising a solution of a copolymer of alkyl and / or alkene-acrylic and / or methacrylic monomers, acrylic or acetic acid and / or their armides substituted on nitrogen by alkyl, alkoxy or methyl groups, additives, fillers, dyes or pigments, the principle being that 1 to 10 propellants are added to the mixture in organic solvents at a temperature of 85-10 ° C. %, based on the total amount of monomers, of the bifunctional organic acid anhydride, preferably maleic anhydride, and the resulting mixture is stirred for 2-4 hours at this temperature.

The actual design depends on the particular composition of the solution. In principle, however, the conventional solution copolymerization is initially carried out under conditions such that an optimum molecular weight is obtained. While the conventional method requires a lower average molecular weight to be sufficient when using the process according to the invention, it follows from the examples.

Further, depending on the content of suitable reactive groups in the copolymer, crosslinking of the copolymer is carried out for the purpose of forming a copolymer. further increasing the viscosity of the solution. However, no foreign direct thixotroping agent is added, but sc adds the required amount r at a temperature of 85-100 ° C, preferably at 92-96 ° C.

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of another suitable bifunctional organic acid anhydride and stirred for 2 to 4 hours at this temperature. Then the solution is cooled and jumped into the shipping containers.

The advantage of this procedure can be evaluated by direct measurement, i.e. cold flow, i.e., plastic deformation of the blind, performed in a vertical position. A layer of glue is applied to the silicone paper substrate with a ruler so that the coating is chipped at a certain rate, for example 20 g / day, dried and the substrate paper, for example, 1.5 cm wide, is pressed by roller. The paper is then peeled off, whereby the adhesive layer is transferred from the silicone paper to the backing paper and adhered to a vertically placed glass plate on a predetermined area (e.g. 5 cm). From the bottom, the sample paper is loaded with a prescribed weight, e.g. The sample is monitored for 24 hours, and the displacement of the bonded surface is measured in the direction of the applied weight.

While commonly produced adhesives are measured in millimeters and often fall off after 24 hours, when using a glue prepared in a protected manner, the cold flow displacement is generally zero, in rare cases reaching a maximum of 0.5 mm.

The production method according to the invention is explained in more detail in the following examples, which, however, are neither limited nor exhausted.

Example 1,

In a 2500 L reactor, a copolymer of a mixture of 150 kg butyl methacrylate 550 kg of 2-ethylhexyl acrylate kg of N-isobutoxymethyl acrylamide 6 kg of acrylic acid in a 80/110 blend of 80 kg toluene 150 kg in the presence of 1.5 kg dibenzoyl peroxide.

The properties of the solution thus prepared are assessed by measuring the flow rate in a standard manner and measuring the theological properties of the solution on a Rheotest 2, where the Ostwald-Waelea equation constants and thixotropic behavior are determined from a series of viscosity measurements at various shear rates. The following values were determined by measuring the prepared solution:

cold flow 4 mm Ostwald equation -de Waelea equation K = 15,385 n = 0.8275 rheological stability 100% increase in viscosity 58,03 mPa.s

Note that n in the equation shows the deviation of the solution from the Newtonian behavior.

16 kg of maleic anhydride are added to the copolymer solution at 92 DEG C. and stirred at this temperature for 3 hours. The solution is then cooled and measured in the same way. The following values were found: cold flow 0 mm Ostwald-de 'Waelea equation K = 42.99 n = 0.5435 rheological stability 98.52% viscosity increase 220.49 mPa.s

The most illustrative comparison is possible by quantifying the viscosities of the two solutions for different shear deformation rates that are close to 0 under cold flow measurement conditions.

Calculations based on the Ostwald-de Wael equation using experimentally found constants are given in the table.

- 8 shear rate Viscosity (apparent) in mPa.s deformation in 1 / s solution without solution treated according to the invention

0.1 5486 12 296 2.1 1597 5 064 4.1 1546 S 257 6.1 1215 1 885 8.1 1150 1 654 10.1 1068 il 486

The table shows the viscosity increase at low shear deformation rates, while under normal processing conditions viscosities are almost equal.

Example 2

In a 2 500 1 ^β θ reactor by solution copolymerization, a solution of copolymer kg of methyl methacrylate prepared 565 kg of 2-ethylhexyl acrylate kg of H-butoxymethylacrylamide 7 kg of methacrylic acid in 80/110 technical gasoline 820 kg of ethyl acetate 100 kg of ethyl alcohol 20 kg

CE With Abiester 26 kg

2.1 kg of iso-bis-isobutyronitrile was used as the initiator of the copolymerization.

Prepared solution; copolymer has the following properties: st flux of 6 mm Ostwald-de Waelea equation K = 19.526 η χ 0.88EE rheological stability 100% viscosity increase 25.21 mPa.s

9 kg of phthalic anhydride are added slowly to the copolymer solution at 96 [deg.] C. and stirred for 4 hours. The mixture was cooled and measured in the same way. The following values were found:

cold flow 0.1 mm * constant of the Ostwald-de Waelea equation E = 18.553

n. = 0.6932 rheological stability 99.1% viscosity increase 101.55 mPa.s

When the treated solution was applied to the substrate, the coating was fully film-forming, without villi and casting defects.

Claims (1)

patent claims Process for the preparation of thixotropic contact acrylate adhesives by copolyraeration of a monomer mixture comprising 15 to 35% by weight of esters of acrylic acid with aliphatic alcohols having a carbon number of 1 to 8, 0.8 to 3% by weight. unsaturated monomers selected from the group consisting of acrylic and methacrylic acid and / or amides thereof substituted on the nitrogen by alkyl, alkoxy or methyl olefins, 5 to 15 wt.% of an alkyl ester of methacrylic acid having a number of carbon atoms in the alkyl. % of a substituent 1 to 6 and optionally 1 to 5 wt.% of additives, dyes or fillers, in the presence of 5 to 75 wt.% of organic solvents, characterized in that it is further 100 ° C adds 1 to 10% by weight, calculated on the total amount of monomers, bifunctional anhydride organic