JP2007307719A - Biodegradable resin member joining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable resin member joining method which has no problem in association with disposal, improves joining force, and can join the biodegradable resin members in a short time. <P>SOLUTION: In the biodegradable resin member joining method, an adhesion sheet containing polylactic acid as a main component is arranged between the biodegradable resin members containing polylactic acid as a main component while the interfaces in contact the biodegradable resin member and the adhesion sheet are heated. When the biodegradable resin members contain poly(D-lactic acid) as a main component, the adhesion sheet contains poly(L-lactic acid) as a main component. When the biodegradable resin members contain poly(L-lactic acid) as a main component, the adhesion sheet contains poly(D-lactic acid) as a main component. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for joining biodegradable resin members.

  Synthetic resins are widely used not only in daily necessities but also in various fields such as structural parts of the machine industry, civil engineering and building materials because of their excellent characteristics. However, since this synthetic resin is hardly decomposed in a natural environment due to its stability, it is a problem in disposal.

  Therefore, in recent years, so-called biodegradable resins that can be decomposed by microorganisms and reduced to the circulation cycle of ecosystems have attracted attention, and various molded articles using the biodegradable resins have been produced.

  By the way, when joining the members of such biodegradable resin moldings or this member to a base material, if a conventional synthetic resin adhesive is used, even if the member is made biodegradable, it is accompanied by disposal. Problems will arise. Therefore, a method is disclosed in which amorphous polylactic acid is used as an adhesive sheet, and the biodegradable resins are bonded to each other by heating to a temperature not lower than the glass transition temperature and not higher than the melting point of the amorphous polylactic acid (for example, (See Patent Document 1).

Since amorphous polylactic acid is used in this method, the entire joined member exhibits biodegradability, and the problem associated with disposal is solved. However, the temperature for bonding must be controlled within a narrow temperature range of not less than the glass transition temperature and not more than the melting point, and it takes time until the softened adhesive sheet is solidified and joined.
JP 2003-292925 A

  An object of the present invention is to solve the above-described problems, and specifically, to provide a method for joining biodegradable resin members that can be joined in a short time without any problems associated with disposal, with improved joining force.

That is, the present invention
<1> Poly-L-lactic acid containing L-lactic acid as a main component between two biodegradable resin members composed of a biodegradable material containing poly-D-lactic acid containing D-lactic acid as a main component A biodegradable resin member joining method comprising: arranging an adhesive sheet made of a biodegradable material containing a material in a state where an interface between the biodegradable resin member and the adhesive sheet is heated.

  <2> Poly-D-lactic acid containing D-lactic acid as a main component between two biodegradable resin members composed of a biodegradable material containing poly-L-lactic acid containing L-lactic acid as a main component A biodegradable resin member joining method comprising: arranging an adhesive sheet made of a biodegradable material containing a material in a state where an interface between the biodegradable resin member and the adhesive sheet is heated.

In the above inventions <1> and <2>, if one of the biodegradable resin member and the adhesive sheet is composed of a biodegradable material containing poly-L-lactic acid, the other is a biodegradable material containing poly-D-lactic acid. Consists of degradable materials. In this case, since a stereocomplex of poly-L-lactic acid and poly-D-lactic acid is formed at the boundary between the biodegradable resin member and the adhesive sheet, the shear strength is increased by chemical bonding and the bonding force is improved. And crystallization (solidification, bonding) in a short time.
Therefore, according to the inventions <1> and <2>, the joining force between the two biodegradable resin members is increased, and the joining can be performed in a short time.
Also, if a stereo complex is formed at least at the interface between the adhesive sheet and the biodegradable resin member, the adhesive sheet and the biodegradable resin member can be joined, so the heating time for joining can be shortened. it can.

  Furthermore, since the whole joined member is biodegradable, according to the inventions <1> and <2>, the constituent members can be discarded without being separated.

<3> The biodegradable resin as described in <1> or <2> above, wherein the heating temperature at the interface is equal to or higher than the melting points of the poly-L-lactic acid and the poly-D-lactic acid. This is a method for joining members.

<4> Furthermore, it pressurizes at the time of the said joining, The joining method of the biodegradable resin member of any one of Claim 1 thru | or 3 characterized by the above-mentioned.

<5> The raw material according to any one of claims 1 to 4, wherein the whole is heated while the biodegradable resin member and the adhesive sheet are joined at the time of joining. It is a joining method of a decomposable resin member.

In the present invention, the biodegradable resin member and the adhesive sheet are joined by forming a stereo complex. Stereocomplexes occur by homogeneous mixing of poly-L-lactic acid and poly-D-lactic acid at the molecular level.
Therefore, the poly-L-lactic acid and the poly-D-lactic acid are mixed by heating so as to be equal to or higher than the melting points of poly-L-lactic acid and poly-D-lactic acid.

  Further, as in the above <4> invention, pressure is applied at the time of joining, or as in the above <5> invention, the whole is heated in a state where the biodegradable resin member and the adhesive sheet are joined. Thereby, members can be joined more firmly.

<6> At least one of the two biodegradable resin members is provided with one or more recesses on a surface in contact with the adhesive sheet, and the adhesive sheet is disposed between the two biodegradable resin members and heated. The biodegradable resin member joining method according to any one of <1> to <4>, wherein a softened adhesive sheet is caused to enter the concave portion when the pressure bonding is performed.

<7> The method for joining biodegradable resin members according to <6>, wherein the recess is a non-through hole or a through hole.

<8> At least one of the two biodegradable resin members is composed of a composite of polylactic acid and biodegradable fibers, and the concave portion is a gap between the biodegradable fibers. The method for joining biodegradable resin members according to <6> or <7>.

  According to the inventions <6> to <8> above, the melt of the adhesive sheet enters into the recesses of the biodegradable resin member and solidifies, so that in addition to the chemical bond of forming a stereocomplex, physically Since it will couple | bond together, members can be joined more firmly.

  According to the present invention, there can be provided a method for joining biodegradable resin members that can be joined in a short time without any problems associated with disposal and with improved joining force.

  In the present invention, as shown in FIG. 1, an adhesive sheet 3 is disposed between biodegradable resin members 1 and 2, and a stereo complex is formed between the biodegradable resin member and the adhesive sheet. In this method, the decomposable resin members 1 and 2 are joined. In the present invention, both the biodegradable resin member to be joined and the adhesive sheet for joining the members are made of polylactic acid.

The material of the biodegradable resin members 1 and 2 will be described.
Biodegradable resin members 1 and 2 are biodegradable materials containing poly-D-lactic acid mainly containing D-lactic acid, or biodegradable materials containing poly-L-lactic acid mainly containing L-lactic acid. It is comprised by. The poly-D-lactic acid containing poly-D-lactic acid as a main component is composed of 70 to 100 mol% of D-lactic acid and 0 to 30 mol% of L-lactic acid or a copolymerization monomer other than lactic acid. . On the other hand, poly-L-lactic acid containing L-lactic acid as a main component is composed of 70 to 100 mol% of L-lactic acid and 0 to 30 mol% of D-lactic acid or a copolymerization monomer other than lactic acid. Say.

As the copolymerizable monomer component other than lactic acid, known copolymerizable monomers (for example, polystyrene, polyamide, etc.) can be used as long as the degradability is not impaired, but the copolymerized monomer component may also be biodegradable. desirable.
As the copolymerization monomer component, for example, oxycarboxylic acid, carboxylic acid ester, lactone, dicarboxylic acid, polyhydric alcohol, etc. that can be copolymerized with lactide can be applied. Polyester, polyether, polycarbonate and the like having a functional group can be applied. It is desirable that the copolymerization monomer component is also biodegradable. Examples of such copolymerizable monomer components include 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and the like.

  In addition, additives such as a plasticizer, a lubricant, a filler, and an ultraviolet absorber may be added to improve the processability of polylactic acid and the physical properties of the molded body.

  When poly-D-lactic acid and poly-L-lactic acid are copolymers (copolymers), any form of a random copolymer, a block copolymer, and a graft copolymer may be used.

As a polymerization method of poly-D-lactic acid and poly-L-lactic acid, known methods such as a condensation polymerization method and a ring-opening polymerization method can be used. For example, lactic acid and other copolymerization monomers can be used as an organic solvent and Dehydration condensation is carried out in the presence of a catalyst, or lactic acid or a copolymerization monomer is once dehydrated to form a cyclic dimer, followed by ring-opening polymerization.
Furthermore, a chain extender can be used to increase the molecular weight of the resulting polylactic acid.

  The molecular weights of poly-D-lactic acid and poly-L-lactic acid are not particularly limited as long as they have sufficient physical properties for the intended application, but generally have a weight average molecular weight of 100,000 to 300,000. Preferably, it is 150,000 to 250,000, more preferably 180,000 to 220,000.

  Poly-D-lactic acid and poly-L-lactic acid may be amorphous polylactic acid in which polymer chains are randomly arranged, and the amorphous polylactic acid may have a temperature, pressure, tension, etc. It may be crystalline polylactic acid in which a part of the polymer chain is oriented when an external factor is applied, and each polymer chain is placed in a morphologically ordered state.

Moreover, the biodegradable resin members 1 and 2 may contain a biodegradable substance in addition to poly-D-lactic acid or poly-L-lactic acid. The biodegradable substance applicable in the present invention is not particularly limited as long as it exhibits biodegradability and does not inhibit the formation of the stereocomplex described below, but biodegradable fibers are used. And since the unevenness | corrugation can be attached | subjected to the surface of the biodegradable resin member 1 and 2, it is preferable from the point which can strengthen joining force. When using biodegradable fiber, it is preferable to use poly-D-lactic acid or poly-L-lactic acid as a matrix and to make a composite reinforced with biodegradable fiber. In this case, the biodegradable fiber is thermally fused and integrated by softening or melting poly-D-lactic acid or poly-L-lactic acid, and at least a part of the biodegradable resin members 1 and 2 has poly-D. -Lactic acid or poly-L-lactic acid is exposed and present.
As the biodegradable fiber, natural fiber such as hemp, cotton, kenaf or the like, or a fiber formed from a biodegradable resin can be used. In this composite, the ratio of polylactic acid to biodegradable fiber is preferably 7: 3 to 3: 7.

Next, the material of the adhesive sheet 3 will be described.
The adhesive sheet 3 is composed of a biodegradable material containing poly-L-lactic acid containing L-lactic acid as a main component or a biodegradable material containing poly-D-lactic acid containing D-lactic acid as a main component. Here, “poly-L-lactic acid containing L-lactic acid as a main component” and “poly-D-lactic acid containing D-lactic acid as a main component” are those indicated by biodegradable resin members 1 and 2. The same is true for the polymerization method and the like.
In the present invention, when the biodegradable resin members 1 and 2 are made of a biodegradable material containing poly-D-lactic acid, the adhesive sheet 3 is made of poly-L-lactic acid and biodegradable. When the resin members 1 and 2 are made of a biodegradable material containing poly-L-lactic acid, the adhesive sheet 3 is made of poly-D-lactic acid.

  Similarly to the biodegradable resin members 1 and 2, the adhesive sheet 3 may contain a biodegradable substance in addition to poly-D-lactic acid or poly-L-lactic acid. The biodegradable substance that can be applied to the adhesive sheet 3 is the same as that of the biodegradable resin members 1 and 2, and biodegradable fibers can also be contained. When the biodegradable fiber is contained in the adhesive sheet 3, the ratio of polylactic acid to biodegradable fiber is preferably about 9: 1 to 6: 4.

  The adhesive sheet 3 is obtained by molding the polylactic acid as a film or sheet by general injection molding, extrusion molding or the like. The thickness of the adhesive sheet is not particularly limited, but is generally about 0.5 mm to 1 mm.

Next, joining of the biodegradable resin members 1 and 2 and the adhesive sheet 3 will be described.
In the present invention, the adhesive sheet 3 is sandwiched between the biodegradable resin members 1 and 2 and joined by forming a stereo complex at least at the interface between the biodegradable resin member 1 or 2 and the adhesive sheet 3. .

The stereo complex will be described.
Poly-L-lactic acid has a left-handed helical structure, whereas poly-D-lactic acid has a right-handed helical structure. Therefore, when these are uniformly mixed at the molecular level, stereospecific binding occurs between the two components. It forms a tighter and stronger crystal structure than the crystal structure formed with poly-L-lactic acid or poly-D-lactic acid alone. This crystal structure is called a stereo complex. By the formation of this stereo complex, the biodegradable resin members 1 and 2 and the adhesive sheet 3 are chemically bonded. Since this chemical bond is tight and strong, the bonding force between the biodegradable resin members 1 and 2 and the adhesive sheet 3 is improved.

The stereocomplex in the polylactic acid polymer can be formed by mixing the poly-D-lactic acid and poly-L-lactic acid in a solution state or a molten state.
Therefore, in joining the biodegradable resin members 1 and 2 and the adhesive sheet 3, heating is performed so that at least an interface where the biodegradable resin member 1 or 2 and the adhesive sheet 3 are in contact is in a molten state. In order to bring poly-D-lactic acid and poly-L-lactic acid into a molten state, it is preferable to heat to a temperature equal to or higher than the melting points of poly-D-lactic acid and poly-L-lactic acid, specifically 170 ° C to 220 ° C. It is more preferable that the temperature is 180 ° C to 210 ° C. However, in the case of containing kenaf fiber in addition to poly-D-lactic acid or poly-L-lactic acid, the heating temperature is preferably 190 ° C. or lower in order to prevent thermal degradation of the kenaf fiber.

Since the crystal structure by the stereocomplex is formed by generating a stereospecific bond between two-component helical structures with different winding directions, the crystal structure is formed by melting and rearranging and arranging the molecules. Compared to the case, the rate of crystallization is extremely high. Therefore, the joining time of the members can be shortened as compared with conventional joining methods.
In addition, the stereo complex only needs to be formed at least at the interface, and can be joined without melting the entire adhesive sheet as in the past. In particular, since polylactic acid takes a long time to crystallize, it takes a long time to join the members. However, in the present invention, polylactic acid only needs to be melted at least at the above-described interface. It can be shortened.

In the case where the biodegradable resin members 1 and 2 are poly-D-lactic acid or a composite of poly-L-lactic acid and biodegradable fibers, the biodegradable fibers on the surfaces to be joined, that is, the surfaces in contact with the adhesive sheet 3 It is preferable that a part of is exposed. When a part of the biodegradable fiber is exposed on the surface, when the adhesive sheet melts at the time of joining, the melt of the adhesive sheet enters the gap between the biodegradable fibers and solidifies, thereby strengthening the member. They can be joined together.
Thereby, in addition to the chemical bond of forming a stereo complex, it is also physically bonded, so the members can be bonded more firmly.

  Moreover, it is also preferable to provide a recessed part in the surface to which the member to be joined is joined. As shown in FIG. 2, the recess may be in the form of a non-through hole 4 or a through hole 5 provided on a surface to be joined of members to be joined. By providing such a recess, the members 3 can be joined more firmly by joining and solidifying the melt 3 of the adhesive sheet into the recess during bonding. As shown in the non-through hole 4 in FIG. 2, the recess is preferably formed with an inclination with respect to the surfaces to be joined. This is because the strength is further increased against peeling. Further, in order to prevent the adhesive sheet 3 softened and melted at the time of joining from flowing out and to enter the recess, it is preferable to provide the flow stop 6 on at least one of the members. This flow stop can also serve as positioning of the members at the time of joining.

  The adhesive sheet 3 is disposed between the biodegradable resin members 1 and 2 manufactured as described above, and the biodegradable resin member 1 is at least at the interface where the biodegradable resin member 1 or 2 and the adhesive sheet 3 are in contact with each other. Then, the biodegradable resin member 2 and the adhesive sheet 3 are heated to a temperature equal to or higher than the melting point to form a stereo complex at the interface.

  As specific heating methods, (1) the surfaces of the biodegradable resin members 1 and 2 on the side in contact with the adhesive sheet 3 are previously heated to melt polylactic acid, and in this state, the biodegradable resin There is a method of sandwiching the adhesive sheet 3 between the members 1 and 2. Also, (2) a method in which the surface of the adhesive sheet 3 is preheated to melt polylactic acid and then sandwiched between the biodegradable resin members 1 and 2, (3) the biodegradable resin members 1 and 2 The surface of the adhesive sheet 3 is heated in advance, and the adhesive sheet 3 is sandwiched between the biodegradable resin members 1 and 2 in this state, (4) the above (1 ) To (3), the method in which the adhesive sheet 3 is sandwiched between the biodegradable resin members 1 and 2 and then bonded while being pressurized, (5) any of the above (1) to (3) Depending on the method, after the adhesive sheet 3 is sandwiched between the biodegradable resin members 1 and 2, the whole is heated while being pressurized.

  When pressurizing at the time of joining, it is preferable to adjust the pressure appropriately in consideration of the strength of the biodegradable resin member 1 and the biodegradable resin member 2 and the strength of the adhesive sheet 3, for example, a pressure of 10 MPa to 20 MPa. Can be added.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
<Production of biodegradable resin member>
Using a clip-shaped member as shown in FIG. 1, compression molding is performed using 300 g of poly-L-lactic acid (manufactured by Toyota Motor Corporation, trade name: U′z-B0, melting point 168 ° C.) and 200 g of kenaf fiber. A plate-like member was manufactured.

<Preparation of adhesive sheet-1>
Using a short fiber (1.7T51 mm) of the poly-D-lactic acid (manufactured by PURAC, trade name: PURASORB PD, melting point 192 ° C.), a non-woven fabric having a basis weight of 100 g / m ² was produced, and an adhesive sheet-1 was formed. .

<Joint>
The respective surfaces of the clip-shaped biodegradable resin member and the plate-shaped biodegradable resin member were heated at 200 ° C. for 3 minutes, the adhesive sheet -1 was sandwiched between them, and the surfaces were left to stand for several hours. .

[Comparative Example 1]
<Production of biodegradable resin member>
Using a clip-shaped member as shown in FIG. 1, compression molding is performed using 300 g of poly-L-lactic acid (manufactured by Toyota Motor Corporation, trade name: U′z-B0, melting point 168 ° C.) and 200 g of kenaf fiber. A plate-like member was manufactured.

<Preparation of adhesive sheet-2>
In the production of the adhesive sheet-1, a poly-D-lactic acid short fiber (1.7 T51 mm) was used as poly-L-lactic acid (manufactured by Toyota Motor Corporation, trade name: U'z-B0, melting point 168 ° C.). Then, a non-woven fabric having a basis weight of 100 g / m ² was produced, and an adhesive sheet-2 was formed.

<Joint>
The respective surfaces of the clip-shaped biodegradable resin member and the plate-shaped biodegradable resin member were heated at 200 ° C. for 3 minutes, and the pressure-sensitive adhesive sheet-2 was sandwiched between the surfaces, and then left for several hours. .

[Comparative Example 2]
<Production of biodegradable resin member>
Using a clip-shaped member as shown in FIG. 1, compression molding is performed using 300 g of poly-L-lactic acid (manufactured by Toyota Motor Corporation, trade name: U′z-B0, melting point 168 ° C.) and 200 g of kenaf fiber. A plate-like member was manufactured.

<Joint>
The respective surfaces of the clip-shaped biodegradable resin member and the plate-shaped biodegradable resin member were heated at 200 ° C. for 3 minutes, and were then pressure-bonded with a clip without interposing an adhesive sheet therebetween, and left for several hours.

[Measurement of viscoelasticity of joints]
The viscoelasticity was measured for the joint part. The measuring method is as follows.
Using a DVE Rheospectr (DVE-V4) manufactured by Rheology Co., Ltd., a tensile test was carried out to measure viscoelasticity. The measurement conditions were a measurement start temperature of −50 ° C., an end temperature of 250 ° C., a temperature increase rate of 3 ° C./min, and a sine wave having a fundamental frequency of 10 Hz.

  The obtained measurement results are shown in FIG. As shown in FIG. 3, the viscoelasticity was higher in Example 1 than in Comparative Example 1 and Comparative Example 2. This is probably because the poly-D-lactic acid of the adhesive sheet-1 and the poly-L-lactic acid of the biodegradable resin member formed a stereo complex at the interface.

[Measurement of adhesive strength at joints]
About the said junction part, Shimadzu Corporation Shimadzu autograph (AG-20KNG) was used, the tension test was implemented with the crosshead moving speed of 10 mm / min, and the adhesive strength was measured.

  The obtained measurement results are shown in FIG. As shown in FIG. 4, the shear strength was higher in Example 1 than in Comparative Example 1 and Comparative Example 2. This is probably because the poly-D-lactic acid of the adhesive sheet-1 and the poly-L-lactic acid of the biodegradable resin member formed a stereo complex at the interface.

[Adhesion speed of joint part]
In Example 1, it was confirmed that the biodegradable resin member could be joined in about 3 minutes at 200 ° C. On the other hand, in Comparative Example 1 and Comparative Example 2, it took about 0.5 to 3 hours for joining. In this example, since the bonding is performed by forming a stereo complex, the bonding time can be shortened as compared with the case of forming a crystal structure by melting and rearranging the molecular arrangement as in the comparative example. It seems to have been.

  In the present invention, as shown in the results of the examples, the formation of a stereo complex increases the shear strength, improves the joining force, and shortens the joining time. Since the whole is biodegradable, the entire member can be decomposed by microorganisms or the like, and can be discarded without separating the constituent members.

1 is a schematic diagram illustrating the method of the present invention. 1 is a schematic diagram illustrating the method of the present invention. It is a graph which shows the result of the viscoelasticity measurement in an Example. It is a graph which shows the measurement result of the adhesive strength in an Example.

Explanation of symbols

1 Biodegradable resin member 2 Biodegradable resin member 3 Adhesive sheet 4 Non-through hole 5 Through hole 6 Flow stop

Claims (8)

  Raw material containing poly-L-lactic acid mainly composed of L-lactic acid between two biodegradable resin members composed of biodegradable material containing poly-D-lactic acid mainly composed of D-lactic acid A bonding method of a biodegradable resin member, wherein an adhesive sheet made of a degradable material is disposed in a state where an interface between the biodegradable resin member and the adhesive sheet is heated.   A living body containing poly-D-lactic acid mainly composed of D-lactic acid between two biodegradable resin members composed of a biodegradable material containing poly-L-lactic acid mainly composed of L-lactic acid. A bonding method of a biodegradable resin member, wherein an adhesive sheet made of a degradable material is disposed in a state where an interface between the biodegradable resin member and the adhesive sheet is heated.   The method for joining biodegradable resin members according to claim 1 or 2, wherein a heating temperature at the interface is a temperature equal to or higher than a melting point of the poly-L-lactic acid and the poly-D-lactic acid. .   Furthermore, it pressurizes at the time of the said joining, The joining method of the biodegradable resin member of any one of Claim 1 thru | or 3 characterized by the above-mentioned.   The biodegradable resin according to any one of claims 1 to 4, wherein the entire biodegradable resin member and the adhesive sheet are heated at the time of joining, and the whole is heated. Member joining method.   At least one of the two biodegradable resin members is provided with one or more recesses on the surface in contact with the adhesive sheet, and when the adhesive sheet is disposed and joined between the two biodegradable resin members The method for joining biodegradable resin members according to any one of claims 1 to 5, wherein the softened adhesive sheet is caused to enter the recess.   The biodegradable resin member joining method according to claim 6, wherein the recess is a non-through hole or a through hole.   7. At least one of the two biodegradable resin members is composed of a composite of polylactic acid and biodegradable fibers, and the concave portion is a gap between the biodegradable fibers. Or the joining method of the biodegradable resin member of Claim 7.

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