Hot-melt adhesive composition and adhesive structure and laminate using the same

Abstract

To provide a hot-melt adhesive composition that is biodegradable and has excellent adhesion to plastics, metals, and other materials, either individually or in combination, as well as adhesive structures and laminates using the same. [Solution] The hot-melt adhesive composition of the present invention contains a thermoplastic component, which is at least one selected from the group consisting of thermoplastic polysaccharides and thermoplastic proteins. According to the present invention, excellent hot-melt adhesion can be provided to substrates made of materials such as plastics and metals, regardless of their type. The adhesive composition of the present invention is also biodegradable and can function as an environmentally friendly hot-melt adhesive. Furthermore, even after bonding two substrates made of the same or different materials, the adhesion can be easily released by applying a predetermined temperature in an environment such as a water bath.

Description

Technical Field

[0001] The present invention relates to a hot melt type adhesive composition, an adhesive structure and a laminate using the same.

Background Art

[0002] In recent years, in order to reduce the environmental impact, materials and products have been made lighter, and the replacement of metal materials with polymer materials or composite materials has become increasingly important. Under such circumstances, adhesion between different materials may be required to combine diverse materials. As an adhesive, hot melt adhesives that do not involve the evaporation of low boiling point organic solvents or water are widely used in industrial applications.

[0003] On the other hand, as biodegradable plastics such as polylactic acid become widespread, biodegradability has come to be desired for adhesives used between materials.

[0004] Glue is a natural polymer material that has been used as an adhesive since ancient times. In addition to having good adhesiveness to wood, glue also has the property of being easily disassembled. Moreover, it itself has the property of biodegradability.

[0005] However, since glue is used as an adhesive in an aqueous solution, it cannot be used as an industrially important hot melt adhesive, and it is difficult to say that it can meet the needs such as adhesion between the above different materials.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention aims to solve the above problems, and its object is to provide a hot melt type adhesive composition having biodegradability and excellent adhesiveness to single or combined materials such as plastics and metals, an adhesive structure and a laminate using the same.

Means for Solving the Problems

[0007] The present invention relates to a hot-melt adhesive composition containing a thermoplastic component, The composition is characterized in that the thermoplastic component is at least one selected from the group consisting of thermoplastic polysaccharides and thermoplastic proteins.

[0008] In one embodiment, the thermoplastic component contains a thermoplastic protein.

[0009] In further embodiments, the hot-melt adhesive composition of the present invention further contains polysaccharides and polyols having α-links.

[0010] In one embodiment, the thermoplastic protein contains at least one natural product-derived protein selected from the group consisting of gelatin, collagen, gluten, soy protein, and okara-derived protein.

[0011] The present invention also relates to an adhesive structure which is a thermally melted and solidified product of the above-mentioned hot-melt adhesive composition.

[0012] In one embodiment, the adhesive structure of the present invention is attached to a substrate layer and can be detached from the substrate layer by a water bath at 35°C to 100°C.

[0013] The present invention also relates to a laminate comprising a base layer and an adhesive layer composed of the above-mentioned adhesive structure.

[0014] In one embodiment, the substrate layer is biodegradable. [Effects of the Invention]

[0015] According to the present invention, excellent hot-melt adhesion can be provided to substrates made of materials such as plastics and metals, regardless of their type. The adhesive composition of the present invention is also biodegradable and can function as an environmentally friendly hot-melt adhesive. Furthermore, even after bonding two substrates made of the same or different materials, the adhesion can be easily released by applying a predetermined temperature in an environment such as a water bath. [Brief explanation of the drawing]

[0016] [Figure 1] (a) is a schematic cross-sectional view illustrating the state in which the test specimens prepared in the examples and comparative examples are sandwiched between two heater units, and (b) is a schematic diagram of the prepared test specimen illustrating the size of the test specimen and the positional relationship of the substrate and adhesive sample used. [Modes for carrying out the invention]

[0017] The present invention will be described in detail below.

[0018] (Hot melt adhesive composition) The hot-melt adhesive composition of the present invention contains a thermoplastic component.

[0019] Herein, the term "for hot-melt bonding" as used in this specification means that the product is intended for bonding to a given substrate by hot melt, and includes, for example, its use as a hot-melt adhesive.

[0020] In the present invention, thermoplastic components include thermoplastic polysaccharides and thermoplastic proteins, as well as combinations thereof.

[0021] Thermoplastic polysaccharides are mixtures that have thermoplastic properties and contain a predetermined polysaccharide and a plasticizer, specifically containing polysaccharides having α-links and polyols.

[0022] In the present invention, the polysaccharide having an α-bond contains various constituent sugars existing in nature. Examples of the polysaccharide having an α-bond include starch, dextrin, α-cyclodextrin, pullulan, agarose, and carrageenan, and combinations thereof. The polysaccharide having an α-bond is preferably starch because it is easily available and can provide excellent adhesiveness to the resulting composition.

[0023] Starch is, for example, derived from plants. For example, starches derived from cereals such as corn, wheat, and rice; beans such as broad beans, mung beans, and adzuki beans; tubers such as potatoes, sweet potatoes, and tapioca; wild grasses such as arrowroot, bracken, and kudzu; and palms such as sago palm; and combinations thereof can be used.

[0024] In the present invention, polyols can function, for example, as plasticizers for the polysaccharide having the above α-bond. Examples of polyols include ethylene glycol (EG), polyethylene glycol (PEG), polypropylene glycol, trimethylolpropane, glycerin-based compounds, sorbitol, pentaerythritol, and derivatives thereof, and combinations thereof.

[0025] Here, polyethylene glycol (PEG) or polypropylene glycol preferably has a weight average molecular weight of 200 to 10000, more preferably 300 to 2000.

[0026] Examples of glycerin compounds include glycerin polyvalent esters such as glycerin, glycerin (mono, di, tri)acetate, glycerin (mono, di, tri)ethylate, and glycerin (mono, di, tri)stearate; polyglycerins such as diglycerin, triglycerin, tetraglycerin, and hexaglycerin; and polyglycerin polyvalent alkyl esters such as diglycerin (mono, di, tri, tetra)acetate, diglycerin (mono, di, tri, tetra)ethylate, diglycerin (mono, di, tri, tetra)stearate, and triglycerin (mono, di, tri, tetra, hepta, hexa)acetate.

[0027] Polyols are preferred, particularly ethylene glycol (EG), polyethylene glycol (PEG), glycerin compounds, trimethylolpropane, and sorbitol, as well as combinations thereof, because they are biodegradable and, for example, have excellent plasticizing effects on the above-mentioned polysaccharides. More preferably, ethylene glycol (EG), polyethylene glycol (PEG), glycerin, and sorbitol are preferred.

[0028] When using a combination of polysaccharides having α-bonds and polyols, the content of the polyols is preferably 5 to 100 parts by mass, more preferably 10 to 80 parts by mass, per 100 parts by mass of the polysaccharide having α-bonds. If the content of polyols is less than 5 parts by mass, the resulting composition may not have appropriate thermoplasticity. If the content of polyols exceeds 100 parts by mass, the polyols may easily bleed out from the resulting composition.

[0029] In the present invention, the polysaccharides having α-bonds and polyols can function together as a type of thermoplastic biomass (thermoplastic polysaccharide) through mixing. For this reason, the hot-melt adhesive composition of the present invention may contain, for example, a mixture of the polysaccharides having α-bonds and polyols as a thermoplastic polysaccharide, preferably thermoplastic starch. Thermoplastic polysaccharides (including thermoplastic starch) are also biodegradable in themselves.

[0030] Such thermoplastic polysaccharides are well known; for example, thermoplastic starch is commercially available. Alternatively, they can be easily produced by those skilled in the art by mixing the above-mentioned polysaccharides (e.g., starch) with polyols.

[0031] Thermoplastic proteins are mixtures that possess thermoplastic properties and contain a predetermined protein and a plasticizer, specifically containing natural product-derived proteins and polyols.

[0032] Natural product-derived proteins that may be contained in thermoplastic proteins are not particularly limited, but include, for example, gelatin, collagen, gluten, soy protein, and okara-derived proteins, as well as combinations thereof. It is preferable that thermoplastic proteins contain gelatin because it is readily available and exhibits excellent adhesion when combined with the above-mentioned thermoplastic polysaccharides. Polyols that may be contained in thermoplastic proteins are not particularly limited, but include, for example, polyols that can be added together with the above-mentioned polysaccharides having α-links.

[0033] When used in combination with naturally derived proteins as thermoplastic proteins, the content of polyols is preferably 5 to 100 parts by mass, more preferably 10 to 80 parts by mass, per 100 parts by mass of naturally derived protein. If the polyol content is less than 5 parts by mass, the resulting composition may not have appropriate thermoplasticity. If the polyol content exceeds 100 parts by mass, the polyols may easily bleed out of the resulting composition.

[0034] Such thermoplastic proteins are well known; for example, thermoplastic gelatin is commercially available. Alternatively, they can be easily produced by those skilled in the art by mixing the above-mentioned natural product-derived proteins (e.g., gelatin) with polyols.

[0035] In the present invention, it is preferable that the thermoplastic component contains a thermoplastic protein. The thermoplastic protein can change its properties from solid to liquid or from liquid to solid at a predetermined temperature. Such a change in properties can be more effectively observed at the temperatures described later (preferably 35°C to 180°C, more preferably 40°C to 1500°C), which can be applied as a hot-melt adhesive. Furthermore, the thermoplastic protein, liquefied by the application of such temperature, can easily adhere to various substrates and function as an adhesive even on its own.

[0036] Furthermore, by combining such thermoplastic proteins with the above-mentioned thermoplastic polysaccharides, and / or polysaccharides and polyols having the above-mentioned α-bonds, the resulting composition can be made even more effective as a hot-melt adhesive.

[0037] For example, if the hot-melt adhesive composition of the present invention contains thermoplastic polysaccharides and thermoplastic proteins, the amount of thermoplastic protein that may be included in the composition is preferably 1 to 10,000 parts by mass, more preferably 3 to 3,000 parts by mass, and even more preferably 5 to 2,000 parts by mass, per 100 parts by mass of the thermoplastic polysaccharides. If the thermoplastic protein content is less than 1 part by mass, the resulting composition may not be able to exhibit sufficient adhesion to various substrates. If the thermoplastic protein content exceeds 10,000 parts by mass, the resulting composition may become hard, and the workability in bonding may deteriorate.

[0038] In this invention, instead of mixing the thermoplastic polysaccharides and / or thermoplastic proteins that constitute the thermoplastic component, as well as the optional polysaccharides and polyols having α-bonds, the hot-melt adhesive composition may be constructed using a material (e.g., a plant-based material) that contains all of these as constituent components. Examples of such materials include grains such as wheat, barley, rye, and oats. In this invention, grains are preferably processed into a powder form (e.g., wheat flour) for reasons such as improving workability.

[0039] The hot-melt adhesive composition of the present invention may also contain water as another solvent component. Examples of water include pure water, deionized water, distilled water, and tap water. The content of the other solvent component is not particularly limited, and an appropriate amount can be selected by those skilled in the art as long as it does not impair the effects of the present invention.

[0040] The hot-melt adhesive composition of the present invention may also contain other components, such as low-molecular-weight organic substances. The content of these other components is not particularly limited, and an appropriate amount can be selected by those skilled in the art.

[0041] The hot-melt adhesive composition of the present invention functions as a hot-melt adhesive in which the thermoplastic component melts when a predetermined temperature is applied, and then solidifies when cooled to, for example, room temperature. The temperature at which melting begins is not particularly limited, but is preferably 35°C to 180°C, more preferably 40°C to 150°C. Therefore, the hot-melt adhesive composition of the present invention easily melts when such a temperature is applied, and then forms an adhesive structure in the form of a hot-melt solidified product when cooled. Furthermore, even after the adhesive structure has been formed, the hot-melt solidified product can be made hot-melt again by exposing the adhesive structure to an environment at the above temperature (for example, a water bath set to preferably 35°C to 100°C). As a result, even after bonding substrates together using the adhesive composition of the present invention as described later, the adhesion of the substrates together can be easily released by exposing them to such a temperature environment.

[0042] (Laminated structure) The laminate of the present invention comprises a substrate layer composed of a substrate and an adhesive layer composed of an adhesive structure obtained from the hot-melt adhesive composition described above.

[0043] The base layer is composed of any material such as plastic (e.g., thermoplastic resin, thermosetting resin), wood, metal (e.g., iron, aluminum, copper, titanium, zinc, and tin, their alloys, and stainless steel), ceramics, and composites thereof, and may be, for example, thin layers such as films and sheets; flat members such as panels and plates; or any other three-dimensional shapes. The laminate of the present invention preferably has at least two base layers composed of the same or different materials, with an adhesive structure placed between the base layers so that the base layers are firmly bonded together.

[0044] In the present invention, it is preferable that the base layer be made of a biodegradable material. For example, if the adhesive structure constituting the adhesive layer is biodegradable, the entire resulting laminate will be biodegradable, further reducing the environmental burden. Examples of biodegradable materials include biodegradable thermoplastic resins and wood, as well as composite materials thereof.

[0045] Examples of biodegradable thermoplastic resins include polylactic acid, polycaprolactone, polybutylene succinate, polyethylene succinate, polyvinyl alcohol, polyglycolic acid, poly(caprolactone / butylene succinate), poly(butylene succinate / adipate), poly(ethylene terephthalate / succinate), poly(butylene adipate / terephthalate), and polyhydroxybutyric acid, as well as combinations thereof.

[0046] Examples of wood include Japanese red pine, Japanese black pine, Japanese yew, ginkgo, Japanese yew, Yezo spruce, Japanese nutmeg, Japanese larch, Japanese umbrella pine, Japanese cypress, Japanese cedar, Japanese hemlock, Japanese fir, Sakhalin fir, Japanese cedar, Japanese cypress, Japanese cypress, Japanese white pine, fir, Agathis, Scots pine, Caribbean pine, clinky pine, Southern yellow pine, spruce, Japanese red cedar, Western red hemlock, Western red cypress, Western red cypress, Western red pine, Western fir, red pine, Japanese red pine, Northern Japanese larch, Ponderosa pine, Radiata pine, Merkus pine, Mexican pine Coniferous trees such as cypress, redwood, and lodgepole pine; Japanese ash, Japanese holly, evergreen oak, Japanese ash, Distylium racemosum, Japanese maple, Japanese pagoda tree, Japanese snowbell, Japanese persimmon, Katsura tree, Phellodendron amurense, Paulownia, camphor tree, chestnut, zelkova tree, Castanopsis sieboldii, cherry, Japanese wingnut, hornbeam species, Japanese linden, Japanese white oak, Japanese white birch, Machilus thunbergii, boxwood, horse chestnut, poplar, false acacia, Japanese elm, alder, beech, magnolia, Japanese white birch, dogwood, Japanese oak, Japanese birch, Manchurian ash, willow species, Japanese mulberry, acacia Mangium, Azobe, Apitong, African Mahogany, Albizia, Yellow Birch, Yellow Poplar, Yellow Meranti, Ipe, Iroko, Elima, Okoume, Obeche, Older, Kapur, Kapok, Kamelele, Karin, Kalophyllum, Gubas, Gelongan, Kempas, Cordia, Ebony, Coccolojua, Coconut, Rubber Tree, Sapele, Jelutong, Jarrah, Jongkon, Silver Beach, Spanish Cedar, Scepter, Soft Maples, Dark Red Meranti, Taun, Dao, Taga Hardwoods such as yasan, teak, nato, hard maple, basswood, balsa, beech, hickory, bubinga, ply, black walnut, black cherry, black bean, perpock, white ash, white oak, white meranti, makore, mahogany, maras, mansonia, melina, mersawa, merbau, mengelis, monkeypod, light red meranti, labra, ramin, lignum vitae, red oak, rosewood, and other hardwoods; as well as combinations thereof.

[0047] The present invention is in high demand for use because, for example, it allows for the mass production of any shape and is also well-suited to the social objective of reducing environmental impact. Therefore, it is preferable that the base layer is composed of or contains a biodegradable thermoplastic resin.

[0048] The thickness of the substrate layer is not particularly limited; for example, if it has a thin layer or plate-like form, it may have a thickness between a few micrometers and a few centimeters. On the other hand, the thickness of the adhesive layer is preferably 0.01 mm to 5 mm, more preferably 0.02 mm to 3 mm. If the thickness of the adhesive layer is less than 0.01 mm, the amount of adhesive structure contained in the adhesive layer is too small, making it difficult to maintain sufficient adhesion to the substrate. If the thickness of the adhesive layer exceeds 5 mm, the adhesion to the substrate hardly changes, and it may be economically uneconomical in that a large amount of adhesive composition is required.

[0049] In the laminate of the present invention, a strong adhesive relationship is maintained between the substrate layer and the adhesive layer because the substrate layer is attached (e.g., bonded) to the adhesive structure contained in the adhesive layer. On the other hand, the adhesive structure constituting the adhesive layer as described above can have its adhesiveness reduced by being exposed to a predetermined temperature, such as a water bath. As a result, the adhesion between the substrate layer and the adhesive layer in the laminate can be released, and the adhesive structure can be easily detached from the substrate constituting these layers.

[0050] Furthermore, the substrate material detached from the laminate may be disposed of in accordance with various laws and regulations, or it may be reused for new bonding using the hot-melt adhesive composition described above. Alternatively, for example, if both the substrate layer and the adhesive layer constituting the laminate are biodegradable, the laminate can be left to decompose naturally in the environment.

[0051] The laminate of the present invention can be used in a variety of products, such as building products, agricultural materials, daily necessities, stationery, electronic and electrical products, vehicle products, and packaging materials or containers for pharmaceuticals, cosmetics, food, etc. [Examples]

[0052] The present invention will be described more specifically below with reference to examples. However, the present invention is not limited to these examples.

[0053] (Evaluation of adhesive properties by tensile testing) To evaluate the adhesive properties of the adhesive samples obtained in the examples and comparative examples, the following tensile tests were performed in accordance with JIS K 6850 Test Method for Tensile Shear Adhesion Strength of Rigid Adheres.

[0054] First, the obtained adhesive sample was preheated at 100°C for 2 minutes, and then pressed at 100°C under 20 MPa for 3 minutes to form a sheet. Next, this sheet-like adhesive sample was cut to a mass of 0.05 g and sandwiched between the first substrate 10 and the second substrate 20 shown in Figure 1(a) to obtain a laminated test piece 100.

[0055] In preparing the test specimen 100, a stainless steel (SUS) plate 48 and an aluminum plate 46 were placed inside two heater units, respectively. Then, between these heater units, the first base material 10, a sheet-like adhesive sample 30, and the second base material 10 were stacked in that order from bottom to top and hot-pressed. The hot-pressing conditions were set for each test specimen prepared, as described later.

[0056] As shown in Figure 1(b), the sheet-like adhesive sample 30 was placed approximately in the center of the test piece 100, that is, within a distance of 12.5 mm from one end 12 (the end opposite the grip 14) of the first base material 10 constituting the test piece 100, and within a distance of 12.5 mm from one end 22 (the end opposite the grip 24) of the second base material 20 constituting the test piece 100.

[0057] The tensile strength of the obtained test specimens was measured using a desktop precision universal testing machine (Shimadzu Corporation) Autograph AGS-1kNX. For the tensile strength measurement, a test speed of 1 mm / min and a distance of 40 mm between the grips 14 were adopted. The results were expressed as follows: the obtained breaking force (N) was divided by the shear area (mm²). 2 The result of dividing by ) is the maximum stress (N / mm²). 2 It was expressed as ).

[0058] (Example 1: Preparation of adhesive sample (E1)) 5.00 g of cornstarch-derived thermoplastic starch (commercial product) was weighed out and added to a twin-screw type mixer (Thermo Fisher Scientific Micro Compounder MiniLab 3) preheated to 130°C and rotating at 50 rpm. The mixer's rotation speed was then increased to 100 rpm and the mixture was melt-kneaded for 10 minutes to obtain adhesive sample (E1).

[0059] 0.05 g of this adhesive sample (E1) was used to prepare test specimens 100 by preheating them in a hot press machine set to 120°C (with the upper and lower heater units shown in Figure 1(a) activated) by clamping them for 30 seconds without applying press pressure, and then hot pressing them at 20 MPa for 2 minutes. The tensile test described above was then performed on the test specimens. The results are shown in Table 1.

[0060] Next, 0.05 g of this adhesive sample (E1) was used as the first substrate 10, a polypropylene (PP) plate (thickness 0.5 mm), and the second substrate 20, an aluminum (Al) plate (thickness 0.5 mm), as shown in Figures 1(a) and (b). The sample was preheated by clamping it in a hot press machine set to 110°C (only the upper heater unit shown in Figure 1(a) was activated) for 30 seconds without applying press pressure, and then hot-pressed at 10 MPa for 2 minutes to prepare test specimens 100, and the tensile test described above was performed. The results are shown in Table 2.

[0061] Furthermore, 0.05 g of this adhesive sample (E1) was used as the first substrate 10, a polylactic acid (PLA) plate (thickness 0.5 mm), and the second substrate 20, an aluminum (Al) plate (thickness 0.5 mm), as shown in Figures 1(a) and (b). The sample was preheated by clamping it in a hot press machine set to 100°C (only the upper heater unit shown in Figure 1(a) was activated) for 30 seconds without applying press pressure, and then hot-pressed at 10 MPa for 2 minutes to prepare test specimens 100, and the tensile test described above was performed. The results are shown in Table 3.

[0062] Furthermore, 0.05 g of this adhesive sample (E1) was used to prepare test specimens 100 by preheating them in a hot press machine set to 60°C (with the upper and lower heater units shown in Figure 1(a) activated) by clamping them for 30 seconds without applying press pressure, using a polylactic acid (PLA) plate (0.5 mm thick) as the first substrate 10 and a polylactic acid (PLA) plate (0.5 mm thick) as the second substrate 20, as shown in Figures 1(a) and (b). After preheating, the specimens were hot-pressed at 10 MPa for 2 minutes, and the tensile test described above was performed. The results are shown in Table 4.

[0063] (Example 2: Preparation of adhesive sample (E2)) Adhesive sample (E2) was obtained in the same manner as in Example 1, except that the amount of thermoplastic starch added was changed to 3.75 g and 1.25 g of thermoplastic gelatin (commercial product) was added. Test specimens were prepared from this adhesive sample (E2) in the same manner as in Example 1, and the tensile test described above was performed. The results are shown in Tables 1 to 4.

[0064] (Example 3: Preparation of adhesive sample (E3)) Adhesive sample (E3) was obtained in the same manner as in Example 1, except that the amount of thermoplastic starch added was changed to 2.50 g and 2.5 g of thermoplastic gelatin (commercial product) was added. Test specimens were prepared from this adhesive sample (E3) in the same manner as in Example 1, and the tensile test described above was performed. The results are shown in Tables 1 to 4.

[0065] (Example 4: Preparation of adhesive sample (E4)) Adhesive sample (E4) was obtained in the same manner as in Example 1, except that the amount of thermoplastic starch added was changed to 1.25 g and the amount of gelatin added to 3.75 g. Test specimens were prepared from this adhesive sample (E4) in the same manner as in Example 1, and the tensile test described above was performed. The results are shown in Tables 1 to 4.

[0066] (Example 5: Preparation of adhesive sample (E5)) Adhesive sample (E5) was obtained in the same manner as in Example 1, except that the amount of thermoplastic starch added was changed to 0 g and 5.00 g of thermoplastic gelatin (commercial product) was added. Test specimens were prepared from this adhesive sample (E5) in the same manner as in Example 1, and the tensile test described above was performed. The results are shown in Tables 1 to 4.

[0067] (Comparative Example 1: Preparation of adhesive sample (C1)) Adhesive sample (C1) was obtained in the same manner as in Example 1, except that 5.00 g of powdered corn starch was used instead of thermoplastic starch. This adhesive sample (C1) did not have thermoplastic properties, and although we attempted to prepare test pieces in the same manner as in Example 1, it was not possible to bond the substrates together.

[0068] (Comparative Example 2: Preparation of Adhesive Sample (C2)) Adhesive sample (C2) was obtained in the same manner as in Example 1, except that 2.50 g of powdered corn starch was used and 2.50 g of powdered gelatin was added instead of thermoplastic gelatin (commercially available). This adhesive sample (C2) did not have thermoplastic properties, and although an attempt was made to prepare test pieces in the same manner as in Example 1, it was not possible to bond the substrates together.

[0069] (Comparative Example 3: Preparation of adhesive sample (C3)) Adhesive sample (C3) was obtained in the same manner as in Example 1, except that thermoplastic gelatin was not added and 5.00 g of powdered gelatin was added. This adhesive sample (C3) did not have thermoplastic properties, and although an attempt was made to prepare test pieces in the same manner as in Example 1, it was not possible to bond the substrates together.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Table 4]

[0074] As shown in Tables 1-4, the adhesive samples (E1)-(E5) obtained in Examples 1-5 showed stronger adhesion to the substrate compared to the samples (C1)-(C3) of Comparative Examples 1-3.

[0075] (Example 6: Preparation of adhesive sample (E6)) 2.50 g of dextrin, 0.50 g of glycerin, 2.50 g of gelatin, and 0.50 g of deionized water were weighed out and added to a twin-screw type compounder (Thermo Fisher Scientific MiniLab 3) preheated to 130°C and rotating at 50 rpm. The compounding process was then increased to 100 rpm and melt-kneaded for 10 minutes to obtain adhesive sample (E6).

[0076] 0.05 g of this adhesive sample (E6) was used as the first substrate 10, a polylactic acid (PLA) plate (thickness 0.5 mm), and the second substrate 20, an aluminum (Al) plate (thickness 0.5 mm), as shown in Figures 1(a) and (b). The samples were preheated by clamping them in a hot press machine set to 100°C (only the upper heater unit shown in Figure 1(a) was activated) for 30 seconds without applying press pressure, and then hot-pressed at 10 MPa for 2 minutes to prepare test specimens 100, and the tensile test described above was performed. The results are shown in Table 5.

[0077] (Example 7: Preparation of adhesive sample (E7)) Adhesive sample (E7) was obtained in the same manner as in Example 6, except that 2.50 g of α-cyclodextrin was used instead of dextrin. Test specimens were prepared from this adhesive sample (E7) in the same manner as in Example 6, and the tensile test described above was performed. The results are shown in Table 5.

[0078] (Example 8: Preparation of adhesive sample (E8)) Adhesive sample (E8) was obtained in the same manner as in Example 6, except that 2.50 g of pullulan was used instead of dextrin. Test specimens were prepared from this adhesive sample (E8) in the same manner as in Example 6, and the tensile test described above was performed. The results are shown in Table 5.

[0079] (Comparative Example 4: Preparation of Adhesive Sample (C4)) Adhesive sample (C4) was obtained in the same manner as in Example 6, except that 2.50 g of agarose was used instead of dextrin. Attempts were made to prepare test specimens from this adhesive sample (C4) in the same manner as in Example 6, but the substrates could not be bonded together, and therefore a tensile test was not performed. The results are shown in Table 5.

[0080] [Table 5]

[0081] As shown in Table 5, the adhesive samples (E6) to (E8) obtained in Examples 6 to 8 were able to bond aluminum (Al) plates and polylactic acid (PLA) plates well due to the use of polysaccharides having α-bonds in their structure. In contrast, the adhesive sample (C4) of Comparative Example 4, which used a polysaccharide (agarose) without α-bonds in its structure, was found to be unable to bond the substrates at all and was confirmed to be unable to function as an adhesive composition.

[0082] (Example 9: Preparation of adhesive sample (E9)) An adhesive sample (E9) was obtained in the same manner as in Example 1, except that 2.50 g of commercially available tapioca-derived thermoplastic starch was used instead of cornstarch-derived thermoplastic starch, and 2.50 g of commercially available thermoplastic gelatin was added.

[0083] 0.05 g of this adhesive sample (E9) was used to prepare test specimens 100 by preheating them in a hot press machine set to 120°C (with the upper and lower heater units shown in Figure 1(a) activated) by clamping them for 30 seconds without applying press pressure, and then hot pressing them at 20 MPa for 2 minutes. The tensile test described above was then performed on the test specimens. The results, along with those for Example 3 using adhesive sample (E3) derived from cornstarch, are shown in Table 6.

[0084] [Table 6]

[0085] As shown in Table 6, the adhesive samples (E3) and (E9) obtained in Examples 3 and 9 exhibited excellent adhesion to the substrate, regardless of the origin of the thermoplastic starch used (corn starch or tapioca starch).

[0086] (Example 10: Preparation of adhesive sample (E10)) 4.00 g of wheat flour (cake flour), 1.00 g of glycerin, and 0.30 g of deionized water were weighed out and added to a twin-screw type mixer (Thermo Fisher Scientific Micro Compounder MiniLab 3) preheated to 120°C and rotating at 50 rpm. The mixer's rotation speed was then increased to 100 rpm and the mixture was melt-kneaded for 10 minutes to obtain adhesive sample (E10).

[0087] 0.05 g of this adhesive sample (E10) was used as the first substrate 10, and an aluminum (Al) plate (thickness 0.5 mm) as the second substrate 20, as shown in Figures 1(a) and 1(b). Test specimens 100 were prepared by preheating them in a hot press machine set to 120°C (with the upper and lower heater units shown in Figure 1(a) activated) for 30 seconds without applying press pressure, and then hot pressing them at 20 MPa for 2 minutes. The tensile test described above was then performed on the test specimens. The results are shown in Table 7.

[0088] [Table 7]

[0089] As shown in Table 7, the adhesive sample (E10) obtained in Example 10 exhibited appropriate adhesion between the substrates used. The wheat flour used in Example 10 contains starch (a polysaccharide with α-links) and gluten (a protein) as constituent components. It is presumed that the coexistence of these with glycerin in the obtained adhesive sample (E10) resulted in the formation of a substantial thermoplastic polysaccharide and thermoplastic protein in the sample, allowing for the confirmation of adhesion between the substrates used.

[0090] (Example 11: Peel test of substrate with adhesive sample placed on it) Multiple test specimens (SUS-SUS test specimens) were prepared by taking 0.05 g of the adhesive sample (E3) obtained in Example 3 and using a stainless steel (SUS) plate (thickness 0.1 mm) as the first substrate 10 and a stainless steel (SUS) plate (thickness 0.1 mm) as the second substrate 20, as shown in Figures 1(a) and 1(b). The specimens were preheated by clamping them in a hot press machine set to 120°C (with the upper and lower heater units shown in Figure 1(a) activated) for 30 seconds without applying press pressure, and then hot pressing them at 20 MPa for 2 minutes.

[0091] The obtained test pieces were placed in a constant temperature bath set to 80°C for one hour, and then removed. When we attempted to separate the SUS substrates by hand, we were able to easily separate them.

[0092] Next, the obtained test specimens were placed in a constant temperature bath set to 80°C for 1.5 hours, and then placed in water at room temperature (25°C). The SUS substrate peeled off naturally without any manual contact.

[0093] On the other hand, when the obtained test pieces were left in water at room temperature (25°C) for 3 hours, and then attempts were made to separate the SUS substrates by hand, they could not be separated. [Industrial applicability]

[0094] The present invention is useful in various industries, such as the fields of resin processing, agriculture, automobiles, electronics and electrical products, pharmaceuticals, cosmetics, food, stationery, and daily necessities. [Explanation of Symbols]

[0095] 10. First substrate 20 Second base material 30 Adhesive Samples 46 Aluminum plate 48 stainless steel plates 100 test specimens

Claims

1. A hot-melt adhesive composition containing a thermoplastic component, A composition wherein the thermoplastic component is at least one selected from the group consisting of thermoplastic polysaccharides and thermoplastic proteins.

2. The hot-melt adhesive composition according to claim 1, wherein the thermoplastic component contains a thermoplastic protein.

3. Furthermore, the hot-melt adhesive composition according to claim 2 further contains a polysaccharide having an α-link and a polyol.

4. The hot-melt adhesive composition according to claim 1, wherein the thermoplastic protein contains at least one natural product-derived protein selected from the group consisting of gelatin, collagen, gluten, soy protein, and okara-derived protein.

5. An adhesive structure which is a heat-melted and solidified product of a hot-melt adhesive composition according to any one of claims 1 to 4.

6. The adhesive structure according to claim 5, which is attached to a substrate layer and can be detached from the substrate layer by a water bath at 35°C to 100°C.

7. A laminate comprising a base layer and an adhesive layer composed of the adhesive structure described in claim 5.

8. The laminate according to claim 7, wherein the base material layer is biodegradable.

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