DE102022105451A1 - Transparent adhesive composition - Google Patents

Abstract

An adhesive composition is proposed 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 gum as thickener;d) water.

Description

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

Aqueous transparent liquid adhesives are primarily used for craft work as well as for simple and uncomplicated repair tasks. Bonding with at least one open-pored or absorbent substrate, such as wood, paper, cardboard, fabric, cork, felt and other textiles, is generally recommended so that the water contained therein can escape better. Petrochemical-based adhesives, such as polyacrylate, polyurethane, polyvinylpyrolidone, polyvinyl alcohol, continue to dominate the field of aqueous, transparent wet adhesives. Aqueous wet adhesives based on starch and their derivatives are increasingly being described. In all cases, a particular challenge compared to solvent-based wet adhesives is their drying behavior in terms of speed and paper curl. In addition, water-based starch adhesives often have storage stability problems, which manifests themselves as a significant change in viscosity and/or a usually brownish discoloration of the liquid adhesive. This is because they can be subject to enzymatic or biological as well as chemical degradation. Retrogradation can also occur. Many starch-based adhesives and pastes are therefore only produced in a solution from a powder and water shortly before they are used as an adhesive.

In the EP 3 094 678 describes the attempt to achieve long-term stability of liquid adhesives by adjusting the pH value in the 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.

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

One of the main problems with the adhesives known from the prior art is to provide a transparent adhesive that at the same time has a high storage stability. In addition, water-based adhesives often have the problem that these adhesives only dry slowly and the adhesive effect is therefore delayed.

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 both in the dried and in the liquid state. During the drying process, starch-based adhesives also tend to shrink significantly in volume, which, especially in many material bonds, leads to tension within the bond and thus a weakening of the strength. When bonding paper, this loss of volume also leads to particularly unsightly paper curling. This can be counteracted somewhat by using polysaccharides, but this usually comes at the expense of the speed of drying and thus the suitability.

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

1. a) Stärke und/oder mindestens ein Stärkederivat;
2. b) mindestens ein Polyol und/oder Harnstoff als Feuchthaltemittel;
3. c) mindestens eine Polycarbonsäure und/oder ein Salz einer Polycarbonsäure und/oder Xanthan als Verdickungsmittel;
4. d) Wasser.

This object is achieved according to the invention by an adhesive composition which contains the following components:

1. a) starch and/or at least one starch derivative;
2. b) at least one polyol and/or urea as a humectant;
3. c) at least one polycarboxylic acid and/or a salt of a polycarboxylic acid and/or xanthan gum as a thickener;
4. d) water.

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

In a particularly preferred embodiment of the adhesive composition according to the invention, component a) is component b) in a proportion of approximately 15% by weight to approximately 45% by weight, preferably approximately 30% by weight to approximately 40% by weight. with a proportion of approximately 5% by weight to approximately 20% by weight, preferably approximately 8% by weight to approximately 12% by weight, component c) with a proportion of approximately 0.1% by weight to approximately 1.5% by weight and water in a proportion of approximately 40% by weight to approximately 60% by weight. The proportions mentioned have proven to be particularly advantageous with regard to tightening behavior and adhesive performance.

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 to be particularly beneficial in terms of tightening behavior, adhesive performance and paper curl.

Component b) advantageously contains at least one compound selected from the group of glycerol, sugar alcohol, such as sorbitol and/or xylitol, polydextrose and 1,2-propylene glycol. These humectants have proven to be particularly beneficial with regard to setting behavior, adhesive performance and paper curl. Glycerin has proven to be particularly advantageous in terms of these properties.

Component c) is advantageously an alkali metal salt of a polycarboxylic acid, in particular sodium alginate and/or a sodium salt of a water-soluble polyacrylic acid and/or carboxymethyl cellulose and/or pectin. These thickeners have proven to be particularly advantageous with regard to tightening behavior, adhesive performance and paper curl. Sodium alginate has proven to be particularly beneficial.

A particularly advantageous embodiment of the adhesive composition according to the invention contains a combination of maltrodextrin, glycerin, sodium alginate and water. As can be seen from the examples below, such a combination is particularly advantageous in terms of tightening behavior, adhesive performance and paper curling.

The proportion of natural, especially renewable components is preferably more than 99% by weight.

As a rule, the adhesive composition according to the invention contains further additives, selected from the group of preservatives, fragrances, pigments, antioxidants, bleaches and defoamers, where the proportion of these additives is a maximum of approximately 2% by weight.

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

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.

Examples:

1. Preparation of the formulations

The solid components according to Table 1 are sucked into water at room temperature under vacuum and stirred for 3 hours. The appropriate amount of glycerin and/or other liquid components is then added to the solution. Subsequently, auxiliary substances, for example preservatives and/or bleaching agents, are added to the formulation. The adhesive compositions produced in this way are then filled into application bottles. Table 1: tested formulations Components Example 1 (cf.) Example 2 (cf.) Example 3 (cf.) Example 4 (cf.) Example 5 (cf.) Example 6 (req.) Example 7 (req.) Example 8 (req.) Example 9 (req.) Starch derivative (HPS) ¹⁾ 27 35 - - - - - - 27 Maltodextrin (HBS) ²⁾ - - 34.9 34.9 35 34.9 29.5 35 - Sucrose 20 9 - 9 - - - - - Glycerin - - 9 - - 9 10 9 10 Sodium alginate - - - 0.8 0.8 0.8 0.9 - 0.9 Polyacrylic acid ³⁾ - - - - - - - 0.2 - sodium - - - - - - 0.1 - citric acid 4 4 - - - - - - - Excipients (e.g. preservatives, stabilizers) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Water 49 51.7 55 55 55 55 59.9 55.4 61.8
1) HPS: Hydroxypropylated potato starch
2) Enzymatically hyper-distributed starch
3) Carbomer

2. Application tests

All application tests were carried out under constant test conditions. For this purpose, the formulations and test materials were soaked for 24 hours at 23 °C / 50% RH before the start of the test. tempered. Color and transparency were assessed visually. The pH values were determined using a calibrated pH meter from Mettler Toldeo. The viscosities were determined using a rotation vicometer from Brookfield with spindle 5 and 20 rpm at 20 ° C.

Paper tightening values as a measure of speed:

When determining the paper tightening values, the time between application of adhesive and paper tear is determined. For this purpose, the adhesive formulation was applied as a bead in the middle of a defined test strip 1x from left to right and a second test strip was pressed on congruently using finger pressure. A stopwatch was immediately activated. The test strips were then pulled apart evenly until the paper was torn 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:

For this purpose, a bead was applied to one end of a test cardboard (40 mm x 233 mm; 300 g/m ² ) and the respective opposite ends were immediately pressed together by hand. While the ends were being joined together, the time was measured until the adhesive maintained the loop tension on its own. During the gluing process, it was checked at regular intervals of approx. 5 seconds by opening the clamping hand to see whether the gluing was holding the inherent tension of the loop on its own. The result is then the arithmetic mean of five individual measurements.

Adhesive performance based on lap shear tests after 24 hours:

To determine the tensile shear strength [N/mm ² ], both wood/wood and wood/aluminum bonds were carried out. Red beech wood, dimensions 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. To do this, apply the adhesive 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 for 1 hour at 1 bar. The overlap area was 20 mm x 15 mm = 300 mm ² . All bonds were tested after 24 hours with a tensile speed of 50 mm/min. A Zwick Z010 tensile testing machine was used.

Paper curl:

A bead was applied to a strip of paper (copy paper) measuring 297 x 52.5 mm, which was glued congruently to a second strip of paper. The paper strips glued together in this way were dried for 1 day and then qualitatively evaluated.

Characteristics:

Table 2: Test results Characteristics Example 1 (cf.) Example 2 (cf.) Example 3 (cf.) Example 4 (cf.) Example 5 (cf.) Example 6 (req.) Example 7 (req.) Example 8 (req.) Example 9 (req.) Look transparent transparent transparent transparent transparent transparent transparent translucent transparent Viscosity [dPas@20°C] RV5/20 rpm 103 shelf stable 107 shelf stable 3.0 shelf stable 80 shelf stable 58 shelf stable 82 shelf stable 65 shelf stable 86 shelf stable 121 shelf stable PH value 4.2 4.5 8.5 7.7 8.0 7.9 8.1 7.5 8.0 Tightening values (seconds) 152 120 52 77 23 25 34 28 35 Loop test [seconds] 65 58 60 49 26 30 35 32 36 Tensile shear strength [N/mm ² ] Wood/wood 2.0 2.4 5.9 3.1 5.4 7.4 4.5 5.1 4.1 Wood/aluminium 1.3 1.6 2.3 1.6 2.3 2.2 2.4 2.3 1.8 Paper curl: minimal medium medium medium strong minimal minimal minimal minimal Conclusion: Very slowly Slowly, paper curl Slow, very thin, paper curl Slowly, paper curl Strong paper curl Fast, powerful, no paper curl Fast, powerful, no paper curl Fast, powerful, no paper curl Fast. Powerful no paper curl

As can be seen impressively from Table 2, the compositions according to the invention according to Examples 6 to 9 show improved properties compared to the comparison compositions from the prior art. The compositions according to the invention are characterized by excellent adhesive performance and the formation of a rapid adhesive bond. At the same time as these advantageous properties, paper curling hardly occurs when paper is glued together.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 3094678 [0003]
• EP 2455436 [0004]
• EP 3008095 [0005]
• EP 3303410 [0007]

Claims (10)

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 gum as a thickener; d) water. Adhesive composition according to Claim 1 , characterized in that component a) is contained in a proportion of approximately 15% by weight to approximately 45% by weight, preferably approximately 30% by weight to approximately 40% by weight, component b) in a proportion from about 5% by weight to about 20% by weight, preferably about 8% by weight to about 12% by weight, component c) with a proportion of about 0.1% by weight to about 12% by weight. 1.5% by weight is contained and water is contained in a proportion of approximately 40% by weight to approximately 60% by weight. Adhesive composition according to one of the Claims 1 or 2 , characterized in that component a) is branched starch, in particular enzymatically branched starch, preferably maltodextrin and/or an alkaline digested starch ether and/or an alkaline digested propoxylated starch. Adhesive composition according to one of the preceding claims, characterized in that component b) contains at least one compound selected from the group of glycerol, sugar alcohol, such as sorbitol and/or xylitol, polydextrose and 1,2-propylene glycol. Adhesive composition according to one of the preceding claims, characterized in that component c) is an alkali metal salt of a polycarboxylic acid, in particular sodium alginate and/or a sodium salt of a water-soluble polyacrylic acid and/or carboxymethyl cellulose and/or pectin. Adhesive composition according to any one of the preceding claims, containing maltodextrin, glycerin, sodium alginate and water. Adhesive composition according to 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 one of the preceding claims, characterized in that further additives selected from the group of preservatives, fragrances, pigments, antioxidants, bleaching agents and defoamers are included, the proportion of these additives being a maximum of approximately 2% by weight. Bottle or tube with an applicator containing an adhesive composition according to one of the Claims 1 until 8th . Use of an adhesive composition according to one of Claims 1 until 8th for bonding open-pored and/or absorbent substrates, in particular for bonding substrates made of paper, cardboard, wood, felt, cork and/or textile material.