Dimensionally stable adhesive composition containing enzyme modified starch

Abstract

The present invention relates to a dimensionally stable adhesive composition comprising an enzyme modified starch and the use of said adhesive composition as a glue stick.

Description

[Technical field]

[0001] The present invention relates to a dimensionally stable adhesive composition comprising an enzyme modified starch and the use of said adhesive composition as a glue stick. [Background technology]

[0002] Glue sticks are commonly known as cylinders filled with a semi-solid adhesive, the contents of which can be pushed out and pulled back in at the end of the stick by rotating a mechanism that works on the screw principle. The first glue sticks were introduced on the market in 1969, and since then there have been extensive efforts to replace the oil-based adhesives originally used with more sustainable alternatives.

[0003] DE 1 811 466 A1 discloses a glue stick which consists of a molding builder formed from a gel of an alkali or ammonium salt of an aliphatic carboxylic acid having 8 to 36 carbon atoms in water and / or a water-miscible organic solvent and a known water-soluble or water-dispersible adhesive as adhesive component.

[0004] WO 03 / 029376 relates to a dimensionally stable soft wear type glue stick made from an aqueous preparation of a synthetic polymer and a soap gel as builder component, where the aqueous preparation of a synthetic polymer is at least predominantly a solvent-free aqueous polyacrylate dispersion or a solid alkali-soluble polyacrylate, both of which have free acid groups.

[0005] WO 2014 / 019001 discloses a stick paste made from an aqueous preparation of an acrylic ester copolymer as adhesive component and a soap gel as builder substance, and contains C as a gel structure-forming soap. 12- C 22 Fatty acids (especially C 14- C 18 The acrylic acid content of the acrylic acid ester is 10 to 25%.

[0006] A drawback of the stick glues described in the prior art is that they continue to depend on petrochemical components. A further approach to forming stick glues based on renewable raw materials is the use of starch.

[0007] DE 19908560 A1 describes a dimensionally stable, soft, abrasive glue stick which consists of an aqueous preparation of starch ether and sucrose as adhesive components and a soap gel as a forming builder structure.

[0008] EP 2 455 436 A1 discloses a highly homogeneous adhesive composition comprising an enzymatically branched starch having a viscosity stability index SI of 1.3 or less, determined by the quotient of the viscosity after 14 days and the viscosity after 2 hours after preparation of the composition.

[0009] WO 2012 / 110594 relates to a glue stick containing an aqueous preparation of at least one hydroxyalkyl-carboxymethyl starch having a viscosity of less than 2,000,000 mPas, measured as a 40% by weight solution in water using a Brookfield RTV viscometer at 20° C., spindle 7, 20 rpm, and soap, as well as a process for its production and its use for planar bonding of substrates, in particular paper, cardboard, wood and / or plastic.

[0010] WO 2014 / 200344 describes an aqueous adhesive composition comprising highly branched starch (HBS) obtained by reacting starch or a starch derivative with glycogen branching enzyme (EC 2.4.1.18) and a carboxymethyl (CM) polysaccharide derivative. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] DE 1811466 A1 [Patent Document 2] WO 03 / 029376 [Patent Document 3] International Publication No. 2014 / 019001 [Patent Document 4] DE 19908560 A1 [Patent Document 5] European Patent Application Publication No. 2455436 [Patent Document 6] International Publication No. 2012 / 110594 [Patent Document 7] International Publication No. 2014 / 200344 Summary of the Invention [Problem to be solved by the invention]

[0012] The starch-based stick glues available in the prior art have the drawback of continuing to have components that date back to fossil resources and that are not or only partially obtained from renewable plant raw materials.Therefore, there remains a need for sustainable compositions that can be used as stick glues.The object of the present invention is therefore to provide a dimensionally stable adhesive composition, in which the traditionally used chemically modified starches are replaced by degraded starches, where it must be ensured that such adhesive compositions have high bond strength and dimensional stability as well as good abrasion resistance. [Means for solving the problem]

[0013] Surprisingly, it has been found that this object is achieved by an aqueous, dimensionally stable adhesive composition according to claim 1. Preferred embodiments are set forth in the dependent claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention therefore firstly relates to a composition comprising, in each case based on the total weight of the adhesive composition: a) at least 10% by weight of enzyme-modified starch, broken down, having a kinematic viscosity of less than 500,000 mPas, measured according to Brookfield, and obtained by modifying native starch with glycogen branching enzyme (EC 2.4.1.18); b) at least 20% by weight sucrose; c) at least 3% by weight C 12 -C 22 A builder selected from fatty acids and / or salts thereof; The present invention relates to a water-based dimensionally stable adhesive composition comprising: Here, the total proportion of starch (especially degradative enzyme-modified starch) and sucrose is less than 65% by weight based on the total weight of the adhesive composition, and the weight ratio of starch (especially degradative enzyme-modified starch) to sucrose is less than 0.70.

[0015] 40 wt% solution in deionized water (K<1μScm -1 The Brookfield kinematic viscosity of starch as ) can be measured in each case individually with a Brookfield DV2T viscometer at a temperature of 20° C., a rotation speed of 20 rpm, using spindle 7 for kinematic viscosities above 50,000 mPas, spindle 6 for kinematic viscosities up to 50,000 mPas and spindle 4 for kinematic viscosities below 10,000 mPas.

[0016] Degraded starches in the context of the present invention are water-soluble starches obtained from native starch granules by gelatinization. Gelatinization is an irreversible, usually thermally induced, process in which starch granules swell in the presence of water, the starch migrates into the aqueous phase and a polymer solution and / or dispersion is formed. Such degraded starches can be chemically modified or degraded, enzymatically modified and especially rearranged. In the context of the present invention, a starch is considered to be sufficiently degraded if, after the gelatinization step, its dynamic viscosity is less than 500,000 mPas, measured according to Brookfield using spindle 7 at a rotation speed of 20 rpm, as a 40% by weight solution in deionized water. In the context of the present invention, the starch proportion of the adhesive composition according to the present invention comprises any polysaccharide based on α-D-glucose, including amylose and amylopectin components. Thus, in addition to the proportion of enzymatically modified degraded starches, the starch proportion also includes chemically modified and / or chemically degraded degraded starches, provided that these are present as polysaccharides as described above.

[0017] To obtain the starch used in the adhesive composition according to the invention, starch can be degraded and then modified using glycogen branching enzymes (EC 2.4.1.18). Normal starch is composed of two components: substantially linear amylose with α-1,4-glycosidic bonds and α-1,6-branched amylopectin. Branching enzymes are enzymes that are able to convert the α-1,4-glycosidic bonds present in amylopectin and amylose into α-1,6 bonds, creating new branching sites. During incubation with degraded starch, the long side chains of amylose and / or amylopectin are displaced as new α-1,6-glycosidic bonds are formed. This leads to a shortening of the average side chain length and a significant reduction in the interaction capacity of the branched molecules. Starch modified by branching enzymes combines a set of functional properties such as low viscosity at high concentrations, no retrogradation and clear solutions with further functional properties such as sufficiently high wet adhesion.

[0018] The invention therefore provides the use of a degradative enzyme modified starch having a dynamic viscosity of less than 500,000 mPas measured according to Brookfield, obtained by treating starch or a starch derivative with a glycogen branching enzyme (EC 2.4.1.18). The degree of branching can vary and depends on the intended application. Usually, it is therefore preferred that the degradative enzyme modified starch has a degree of molecular branching of at least 4%. In a preferred embodiment, the degradative enzyme modified starch has a degree of molecular branching of at least 5.0% as a component of the adhesive composition according to the invention. This results in a highly stable product. In this context, the degree of branching is preferably at least 5.5%, for example in the range of about 5.5 to about 6.5%. The degree of molecular branching as used herein refers to the relative amount of α-1,6-glycosidic bonds relative to the total amount of α-1,6- and α-1,4-glycosidic bonds ((α-1,6 / (α-1,6+α-1,4)*100%) and can be determined by methods known in the art. Typically, and therefore preferably, the degree of branching in the context of the present invention does not exceed 8.0%, very particularly preferably does not exceed 7.5%.

[0019] Preferably, the starch or starch derivative is first degraded before contacting it with the branching enzyme. As already mentioned above, starch gelatinization is a process that breaks and opens the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (hydroxyl hydrogen and oxygen) to absorb more water. The starch granules are thereby irreversibly dissolved. The penetration of water increases the randomness of the overall granular structure and reduces the number and size of the crystalline regions. The gelatinized starch can be brought to the desired pH by adding an acid or base. After reaching the desired temperature, the branching enzyme is added and the solution is maintained at the desired temperature for the desired time. Alternatively, the branching enzyme can be added to the starch suspension at room temperature and the slurry is heated to the desired temperature with stirring and held at this temperature for the desired time.

[0020] The branching enzyme can be derived from any suitable microbial source, preferably from a thermostable glycogen branching enzyme obtained from a mesophilic or thermophilic organism, preferably Aquifex aeolicus, Anaerobranca gottschalkii or Rhodothermus obamensis.

[0021] In the context of the present invention, it has surprisingly been found that when degraded enzyme-modified starch is used, the compositions previously described for stick glues do not result in dimensionally stable adhesive compositions, which is why the limitations of the total proportion of starch and sucrose are indicated. It has therefore been found that, in the context of the present invention, in order to achieve particularly advantageous properties, in particular with regard to dimensional stability and abrasion resistance, the total proportion of starch in the adhesive composition according to the invention should be kept within strictly defined limits. Preferred are therefore embodiments in which the total proportion of starch (in particular degraded enzyme-modified starch) and sucrose is less than 60% by weight, but preferably more than 40% by weight, particularly preferably more than 45% by weight, in each case based on the total weight of the adhesive composition.

[0022] A glue stick is characterized in particular by a combination of properties, in addition to sufficient adhesive strength, of abrasion resistance, dimensional stability and compressive strength, which must be coordinated with one another. To this end, it has surprisingly been found that the desired combination of properties can be achieved, in particular when the adhesive composition has starch and sucrose in a weight ratio of less than 0.70. By adapting this weight ratio, the properties of the adhesive composition according to the invention can be further improved, whereby embodiments are preferred in which the weight ratio of starch (in particular degraded enzyme-modified starch) to sucrose is less than 0.60, preferably greater than 0.30. If the weight ratio is more than 0.70, the required compressive strength and abrasion resistance of the adhesive composition cannot be achieved, whereby compressive strength in the context of the present invention is the maximum load measured parallel to the longitudinal axis at which the stick-shaped adhesive composition disintegrates under a compressive load. A decrease in adhesive strength was observed at weight ratios of less than 0.30.

[0023] The starch contained in the adhesive composition of the invention is characterized by a dynamic viscosity of less than 500,000 mPas. In a preferred embodiment, the dynamic viscosity of the degradative enzyme modified starch is less than 200,000 mPas, preferably less than 100,000 mPas, particularly preferably less than 50,000 mPas, but preferably at least 10,000 mPas, where the dynamic viscosity is measured as described above. For most applications, a dynamic viscosity of at least 10,000 mPas is preferred, since at dynamic viscosities of less than 10,000 mPas, in addition to the lower viscosity and the need for longer processing times, an undesirable change in the color of the adhesive composition may also be observed at high temperatures. On the contrary, it has surprisingly been found that a dynamic viscosity of less than 200,000 mPa·s suppresses gel formation and recrystallization in the adhesive composition, resulting in a homogeneous, storage-stable adhesive composition. By further reducing the dynamic viscosity to less than 100,000 mPas, preferably less than 50,000 mPas, the pumpability and filling properties of the adhesive composition in the liquid and heated state could be significantly improved. The viscosity range of 10,000-50,000 mPas was identified as a good compromise between process duration and energy requirements and the provision of a sufficiently degraded starch to obtain sufficient adhesive strength and color stability of the adhesive composition of the invention. Furthermore, this viscosity range allows the production of cylindrical adhesive compositions required for application as stick glues to achieve fewer rejects as a result of misfilling of stick sleeves and an overall reduction in downtime during filling.

[0024] The starch raw material used for the degradative enzyme modified starch used in the adhesive composition of the invention is preferably a starch of natural origin. This may be any conventional tuber, cereal or legume starch, such as pea starch, corn starch including waxy corn starch, potato starch including waxy potato starch, amaranth starch, rice starch including waxy rice starch, wheat starch including waxy wheat starch, barley starch including waxy barley starch, tapioca starch or sago starch. In a preferred embodiment, the degradative enzyme modified starch is obtained from cereals, tubers, roots and / or legumes, preferably from tubers, particularly preferably from sweet potato and / or potato, and especially preferably from potato.

[0025] Starches of natural origin generally have an amylose content of 20% to 40%, depending on the plant species from which they are obtained. This amylose content is also preferred in the context of the present invention. However, there are also amylopectin-rich starches with a significantly increased amylopectin content and products with an increased amylose content. Starches with a high amylopectin content can be degraded and enzymatically hydrolyzed in the context of the present invention in the context of the adhesive composition of the present invention, and starches with an amylopectin content of more than 80% can also be used here. Amylopectin is already a branched starch, and the enzymatic modification according to the present invention using branching enzymes can further increase this already naturally high branching.

[0026] Since starch is naturally heterogeneous, in addition to starch molecules, other starch molecules having the above-mentioned properties may also be present in the enzymatically branched starch prepared according to the invention for the adhesive composition, in the ranges preferred according to the invention. In a preferred embodiment, the proportion of enzymatically modified starch is at least 65% by weight, preferably at least 80% by weight, particularly preferably at least 90% by weight, based on the total starch proportion.

[0027] The adhesive composition of the invention is characterized in that it is obtained mainly from natural raw materials. Thus, preferred are embodiments in which the proportion of degraded chemically modified starch, in particular hydroxyalkyl-carboxymethyl-modified starch, is preferably less than 20% by weight, particularly preferably less than 10% by weight and very particularly preferably less than 5% by weight, based on the total starch proportion. Chemically modified starches are in particular those obtained as products of condensation between hydroxyl groups of anhydroglucose units (AGE) of starch molecules and alcoholic hydroxyl groups of other compounds. However, in a particular embodiment, in order to adjust the rheological properties for liquid filling of the adhesive composition of the invention in the industrial production of glue sticks, it may be advantageous in the adhesive composition of the invention to have at least 0.1% by weight, preferably at least 1.0% by weight, but preferably less than 5.0% by weight, particularly preferably less than 3.0% by weight, of hydroxyalkyl-carboxymethyl-modified starch, in each case based on the total weight of the adhesive composition.

[0028] The builder structure of the adhesive composition of the present invention is 12 -C 22 In a preferred embodiment, at least 4% by weight, preferably at least 5% by weight, but preferably no more than 10% by weight, of C, in each case based on the total weight of the adhesive composition. 12 -C 22 A builder selected from fatty acids and / or salts thereof is included in the adhesive composition of the present invention. The builder structure is preferably C 14 -C 18 It is preferably selected from fatty acids and / or their salts. Particularly preferably, the salts of the builder structures are the sodium, potassium or calcium salts of the corresponding fatty acids or mixtures of these salts.

[0029] The adhesive composition of the present invention is water-based. Water-based adhesive composition can be understood in the context of the present invention to mean an adhesive composition that contains at least 5 wt.% water based on the total weight of the adhesive composition. In a preferred embodiment, the adhesive composition of the present invention contains at least 10 wt.%, preferably at least 15 wt.%, particularly preferably at least 20 wt.%, and especially preferably at least 25 wt.% water based on the total weight of the adhesive composition.

[0030] The adhesive composition of the present invention preferably has a pH value of at least 9.0, particularly preferably at least 9.5, but preferably not more than 11.0. The pH value of the adhesive composition can be adjusted using conventional alkaline reacting substances such as sodium hydroxide, and the pH value is measured directly as a property of the adhesive composition in a liquefied mass at 80° C. using a pH-sensitive glass electrode after calibration with standard buffer solutions.

[0031] In one particularly preferred embodiment, the adhesive composition of the present invention comprises the following components: a) 10-25% by weight of degraded enzyme-modified starch having a kinematic viscosity of less than 500,000 mPas, measured according to Brookfield, and obtained by modifying native starch with glycogen branching enzyme (EC 2.4.1.18); b) 20-45% by weight of sucrose; c) 3 to 10% by weight of C 12 -C 22 a builder selected from fatty acids and / or salts thereof; d) at least 20% by weight water; e) less than 5% by weight of degraded chemically modified starch; and, where applicable, f1) at least 0.1% by weight, preferably at least 1.0% by weight, but preferably less than 3.0% by weight, of hydroxyalkyl-carboxymethyl-modified starch and preferably less than 3% by weight, particularly preferably less than 1% by weight, of degraded chemically modified starch that is not hydroxyalkyl-carboxymethyl-modified starch; or f2) less than 3% by weight, preferably less than 1% by weight, of degraded chemically modified starch; The weight percentages are in each case based on the total weight of the adhesive composition.

[0032] The adhesive composition of the present invention is particularly suitable for use as a glue stick. Accordingly, the present invention further relates to a glue stick formed from the adhesive composition of the present invention.

[0033] The present invention also relates to the use of the glue stick of the present invention for surface-to-surface bonding of substrates, in particular for bonding paper, cardboard and / or plastic to one another. EXAMPLES

[0034] The present invention will now be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the invention in any way.

[0035] Exemplary formulations are summarized in Table 1, where data designated in weight percent are expressed relative to the total weight of the composition. The resulting adhesive compositions were measured and the results are shown in Table 1.

[0036] [Table 1]

[0037] A 10kN Pro Line test device from Zwick Roell is used to measure the compressive strength.

[0038] A 30 mm length of glue cut just above the piston is inserted between two holding pieces; these are stainless steel discs about 10 mm thick with a circular recess of 3 mm to match the diameter of the relevant stick. The stick with the holding pieces is placed in the centre of the test platform of the compression strength tester. The height of the measuring head is adapted to the height of the test part. The measuring head is then moved towards the stick to be tested with a feed rate of 120 mm / min. The highest compressive force reached gives the compressive strength in N. For a diameter of 21 mm, the compressive strength of the glue stick should be between 60 and 120 N.

[0039] As can be seen from the data presented, the adhesive compositions of the present invention are characterized, inter alia, by a combination of high compressive strength, good abrasion resistance, and high adhesive strength.

Claims

1. In each case, based on the total weight of the adhesive composition, a) at least 10% by weight of a degraded enzyme-modified starch having a kinematic viscosity of less than 500,000 mPa·s as measured according to Brookfield and obtained by modifying native starch with glycogen branching enzyme (EC 2.4.1.18); b) at least 20% by weight of sucrose; c) a builder selected from at least 3% by weight of C １２ -C ２２ fatty acids and / or salts thereof; An aqueous, dimensionally stable adhesive composition containing wherein the total proportion of starch, especially the degraded enzyme-modified starch, and sucrose is less than 65% by weight based on the total weight of the adhesive composition, and the weight ratio of starch, especially the degraded enzyme-modified starch, to sucrose is less than 0.70, An aqueous, dimensionally stable adhesive composition.

2. The adhesive composition according to claim 1, characterized in that the total proportion of starch, especially the degraded enzyme-modified starch, and sucrose is less than 60% by weight based on the total weight of the adhesive composition, preferably more than 40% by weight, particularly preferably more than 45% by weight.

3. The adhesive composition according to claim 1, characterized in that the weight ratio of starch, especially the degraded enzyme-modified starch, to sucrose is less than 0.60, preferably greater than 0.

30.

4. The adhesive composition according to claim 1, characterized in that the kinematic viscosity of the degraded enzyme-modified starch is less than 200,000 mPa·s, preferably less than 100,000 mPa·s, particularly preferably less than 50,000 mPa·s, but preferably at least 10,000 mPa·s.

5. The adhesive composition according to claim 1, characterized in that the degraded enzyme-modified starch is obtained from cereals, tubers, roots and / or leguminous plants, preferably from tubers, particularly preferably from sweet potatoes and / or potatoes, and most preferably from potatoes.

6. The adhesive composition according to claim 1, characterized in that the proportion of enzymatically degraded starch is at least 65% by weight, preferably at least 80% by weight, particularly preferably at least 90% by weight, based on the total starch proportion.

7. The adhesive composition according to claim 1, characterized in that the proportion of degraded chemically modified starch, especially hydroxyalkyl-carboxymethyl-modified starch, is preferably less than 20% by weight, particularly preferably less than 10% by weight, very particularly preferably less than 5% by weight, based on the total starch proportion.

8. In each case, the adhesive composition contains at least 4% by weight, preferably at least 5% by weight, but preferably 10% by weight or less, based on the total weight of the adhesive composition, of C １２ -C ２２ The adhesive composition according to claim 1, characterized by containing a builder selected from fatty acids and their salts.

9. C １２ -C ２２ The fatty acid salt is selected from sodium salts, potassium salts, and / or calcium salts, and the adhesive composition according to claim 1 is characterized in that.

10. The adhesive composition according to claim 1, containing at least 10% by weight, preferably at least 15% by weight, particularly preferably at least 20% by weight, and especially preferably at least 25% by weight of water, based on the total weight of the adhesive composition.

11. The adhesive composition according to claim 1, characterized in that it has a pH value of at least 9.0, preferably at least 9.5, but preferably 11.0 or less.

12. a) 10 to 25% by weight of a degraded enzyme-modified starch having a kinematic viscosity of less than 500,000 mPa·s as measured according to Brookfield and obtained by modifying native starch using glycogen branching enzyme (EC 2.4.1.18); b) 20 to 45% by weight of sucrose; c) 3 to 10% by weight of a builder selected from C １２ -C ２２ fatty acids and / or their salts; d) at least 20% by weight of water; and e) less than 5% by weight of degraded chemically modified starch; and, where applicable f1) at least 0.1% by weight, preferably at least 1.0% by weight, but preferably less than 3.0% by weight of hydroxyalkyl-carboxymethyl-modified starch, and preferably less than 3% by weight, particularly preferably less than 1% by weight, of degraded chemically modified starch that is not hydroxyalkyl-carboxymethyl-modified starch; or f2) less than 3% by weight, preferably less than 1% by weight, of degraded chemically modified starch comprising, the % by weight being in each case based on the total weight of the adhesive composition, the adhesive composition according to claim 1.

13. A stick paste formed from the adhesive composition according to at least one of claims 1 to 12.

14. Use of the stick paste according to claim 13 for surface-to-surface bonding of substrates, in particular for bonding paper, cardboard and / or plastics to one another.