Transparent adhesive composition

Abstract

The invention relates to an adhesive composition containing at least the following components: a) starch and / or at least one starch derivative; b) at least one polyol and / or urea as a humectant; c) at least one polycarboxylic acid and / or a salt of a polycarboxylic acid and / or xanthan as a thickening agent; d) water.

Description

[0001] Transparent adhesive composition

[0002] The present invention relates to a transparent water-based adhesive composition.

[0003] Aqueous, transparent liquid adhesives are primarily used for handicrafts and simple, straightforward repairs. Bonding with at least one open-pored or absorbent substrate, such as wood, paper, cardboard, fabric, cork, felt, and other textiles, is generally recommended to allow the water contained within them to escape more easily. Petrochemical-based adhesives, such as polyacrylate, polyurethane, polyvinylpyrrolidone, and polyvinyl alcohol, continue to dominate the field of aqueous, transparent wet adhesives. Starch-based aqueous wet adhesives and their derivatives are also increasingly being described. In all cases, their drying behavior in terms of speed and paper curl poses a particular challenge compared to solvent-based wet adhesives.In addition, water-based starch adhesives often exhibit storage stability problems, which manifest themselves as a significant change in viscosity and / or a usually brownish discoloration of the liquid adhesive. These adhesives can be subject to enzymatic, biological, and chemical degradation. Retrogradation can also occur. Therefore, many starch-based adhesives and pastes are prepared from a powder and water solution shortly before application.

[0004] EP 3 094 678 describes an attempt to achieve long-term stability in liquid adhesives by adjusting the pH to an acidic range between 3.0 and 6.0 by adding organic carboxylic acids. EP 2 455 436 describes the use of enzymatically highly branched starches in adhesives to achieve long-term stability.

[0005] EP 3 008 095 describes the combination of highly branched starches with carboxymethylated polysaccharide derivatives as thickeners in liquid adhesives.

[0006] One of the main problems with current adhesives is providing a transparent adhesive that also offers high storage stability. Furthermore, water-based adhesives often have the problem that they dry slowly, resulting in a delayed bonding effect.

[0007] In EP 3 303 410, the task of increasing bonding speed is solved by adding clay minerals, which, however, is accompanied by a loss of transparency in both the dried and liquid states. During the drying process, starch-based adhesives also tend to experience significant volume shrinkage, which, particularly in the case of many material bonds, leads to tension within the bond and thus a weakening of the bond strength. In paper bonds, this volume shrinkage also leads to particularly unsightly paper curling. This can be counteracted somewhat by using polysaccharides, but this usually comes at the expense of drying speed and thus the setting behavior.

[0008] The present invention is based on the problem of providing an adhesive composition which overcomes the problems known from the prior art.

[0009] This object is achieved according to the invention by an adhesive composition which contains the following components: a) starch and / or at least one starch derivative; b) at least one polyol and / or urea as a humectant; c) at least one polycarboxylic acid and / or a salt of a polycarboxylic acid and / or xanthan as a thickener; d) water.

[0010] It was surprisingly found that the adhesive composition according to the invention is particularly characterized by its rapid setting behavior (speed), very good adhesive performance (tensile shear strength) and negligible paper curl while maintaining transparency and high storage stability.

[0011] In a particularly preferred embodiment of the adhesive composition according to the invention, component a) is present in a proportion of approximately 15% to approximately 45% by weight, preferably approximately 30% to approximately 40% by weight, component b) in a proportion of approximately 5% to approximately 20% by weight, preferably approximately 8% to approximately 12% by weight, component c) in a proportion of approximately 0.1% to approximately 1.5% by weight, and water in a proportion of approximately 40% to approximately 60% by weight. These proportion ranges have proven particularly advantageous, especially with regard to pull-in behavior and adhesive performance.

[0012] Component a) is advantageously branched starch, in particular enzymatically branched starch, preferably maltodextrin and / or an alkaline-digested starch ether and / or an alkaline-digested propoxylated starch. Maltodextrin, in particular, has proven particularly advantageous with regard to pull-on behavior, adhesive performance, and paper corrugation.

[0013] Component b) advantageously contains at least one compound selected from the group consisting of glycerin, sugar alcohols, such as sorbitol and / or xylitol, polydextrose, and 1,2-propylene glycol. These humectants have proven particularly advantageous with regard to pull-on behavior, adhesive performance, and paper curl. Glycerin has proven particularly advantageous with regard to these properties.

[0014] Component c) is advantageously an alkali salt of a polycarboxylic acid, in particular sodium alginate and / or a sodium salt of a water-soluble polyacrylic acid and / or carboxymethylcellulose and / or pectin. These thickeners have proven particularly advantageous with regard to settling behavior, adhesive performance, and paper corrugation. Sodium alginate has proven particularly advantageous.

[0015] A particularly advantageous embodiment of the adhesive composition according to the invention contains a combination of maltodextrin, glycerin, sodium alginate, and water. As can be seen from the examples below, such a combination is particularly advantageous with regard to pull-off behavior, adhesive performance, and paper corrugation.

[0016] Preferably, the proportion of natural, in particular renewable, components is more than 99% by weight.

[0017] As a rule, the adhesive composition according to the invention contains further additives selected from the group of preservatives, fragrances, pigments, antioxidants, bleaching agents and defoamers, where the proportion of these additives is a maximum of approximately 2 wt.%.

[0018] The present invention further relates to a tube or bottle with applicator containing an adhesive composition according to the invention.

[0019] The present invention further relates to a use of an adhesive composition according to the invention for bonding open-pored and / or absorbent substrates, in particular for bonding substrates made of paper, cardboard, wood, felt, cork and / or textile material.

[0020] Examples:

[0021] 1. Preparation of the formulations

[0022] The solid components according to Table 1 are vacuum-suspended in water at room temperature and stirred for 3 hours. The appropriate amount of glycerin and / or other liquid components is then added to the solution. Subsequently, excipients, such as preservatives and / or bleaching agents, are added to the formulation. The resulting adhesive compositions are then filled into application bottles.

[0023] 1) HPS: Hydroxypropylated potato starch

[0024] 2) Enzymatically hyperbranched starch

[0025] 3) Carbomer

[0026] Table 1 : tested formulations

[0027] 2. Application-related tests

[0028] All application tests were conducted under constant test conditions. The formulations and test materials were held at 23°C / 50% RH for 24 hours prior to testing. Color and transparency were assessed visually. pH values ​​were determined using a calibrated Mettler-Toldeo pH meter. Viscosities were determined using a Brookfield rotational viscometer with a spindle of 5 and 20 rpm at 20°C.

[0029] Paper suit values ​​as a measure of speed:

[0030] When determining the paper pull-in values, the time between adhesive application and paper tear is measured. For this purpose, the adhesive formulation was applied as a bead on a defined test strip centered 1x from left to right, and a second test strip was pressed onto the strip using finger pressure to ensure it was congruent. A stopwatch was immediately activated. The test strips were then pulled apart evenly until the paper tear occurred, and the time was determined. The result is the arithmetic mean of five individual measurements. Loop test as a measure of the speed of bonding under tension:

[0031] For this purpose, a bead was placed on one end of a test cardboard (40 mm x 233 mm; 300g / m 2) was applied and the opposite ends were immediately pressed together by hand. While the ends were being joined, the time it took for the adhesive to self-maintain the loop tension was measured. During the bonding process, the clamping hand was opened at regular intervals of approximately five seconds to check whether the adhesive was self-maintaining the loop's inherent tension. The result is then calculated as the arithmetic mean of five individual measurements.

[0032] Adhesive performance based on tensile shear tests after 24 hours:

[0033] To determine the tensile shear strength [N / mm 2] Both wood / wood and wood / aluminum bondings were performed. Red beech wood, measuring 85 mm x 20 mm x 3 mm, and aluminum test specimens from Rocholl were used. For this purpose, the adhesive formulation to be tested was applied to one side of each of two wooden test specimens. The adhesive was applied evenly with a notched trowel over a length of at least 15 mm but no more than 20 mm. The test specimens were then placed overlapping one another and pressed together for 1 hour at 1 bar. The overlap area in each case was 20 mm x 15 mm = 300 mm. 2 All bonds were tested after 24 hours at a tensile speed of 50 mm / min. A Zwick Z010 tensile testing machine was used.

[0034] Paper curl:

[0035] A bead was applied to a 297 x 52.5 mm paper strip (copy paper), which was then bonded to a second paper strip in a congruent manner. The bonded paper strips were dried for 1 day and then qualitatively evaluated. Properties:

[0036] Table 2: Test results

[0037] As Table 2 clearly shows, the inventive compositions according to Examples 6 to 9 exhibit improved properties compared to the comparative compositions from the prior art. The inventive compositions are characterized by excellent adhesive performance and the formation of a rapid adhesive bond. In addition to these advantageous properties, paper curling is virtually nonexistent when bonding paper.

Claims

Patent claims: Adhesive composition comprising at least the following components: a) starch and / or at least one starch derivative; b) at least one polyol and / or urea as a humectant; c) at least one polycarboxylic acid and / or a salt of a polycarboxylic acid and / or xanthan gum as a thickener; d) water. Adhesive composition according to claim 1, characterized in that component a) is present in a proportion of approximately 15 wt.% to approximately 45 wt.%, preferably approximately 30 wt.% to approximately 40 wt.%, component b) is present in a proportion of approximately 5 wt.% to approximately 20 wt.%, preferably approximately 8 wt.% to approximately 12 wt.%, component c) is present in a proportion of approximately 0.1 wt.% to approximately 1.5 wt.%, and water is present in a proportion of approximately 40 wt.% to approximately 60 wt.%.Adhesive composition according to claim 1 or 2, characterized in that component a) is branched starch, in particular enzymatically branched starch, preferably maltodextrin and / or an alkaline starch ether and / or an alkaline propoxylated starch. Adhesive composition according to any of the preceding claims, characterized in that component b) is at least one compound. Selected from the group consisting of glycerin, sugar alcohols such as sorbitol and / or xylitol, polydextrose, and 1,2-propylene glycol. Adhesive composition according to any one of the preceding claims, characterized in that component c) is an alkali salt of a polycarboxylic acid, in particular sodium alginate, and / or a sodium salt of a water-soluble polyacrylic acid, and / or carboxymethylcellulose, and / or pectin. Adhesive composition according to any one of the preceding claims, containing maltodextrin, glycerin, sodium alginate, and water. Adhesive composition according to any one of the preceding claims, characterized in that the proportion of natural, in particular renewable, components is more than 99% by weight.Adhesive composition according to any one of the preceding claims, characterized in that it contains further additives selected from the group consisting of preservatives, fragrances, pigments, antioxidants, bleaching agents, and defoamers, wherein the proportion of these additives is a maximum of approximately 2% by weight. Bottle or tube with an applicator containing an adhesive composition according to any one of claims 1 to 8. Use of an adhesive composition according to any one of claims 1 to 8 for bonding open-pored and / or absorbent substrates, in particular for bonding substrates made of paper, cardboard, wood, felt, cork, and / or textile material.

Images