Biodegradable resin composition and molding

Abstract

To provide a biodegradable resin composition and a molding which have both moldability and degradability.SOLUTION: A biodegradable resin composition contains a biodegradable polyester resin and an additive, contains, with respect to 100 mass% of the biodegradable polyester resin, 70 mass% or more and 100 mass% or less of polybutylene succinate adipate, 0 mass% or more and 30 mass% or less of polybutylene succinate, and 0 mass% or more and 30 mass% or less of polybutylene adipate terephthalate, contains, as additives, with respect to 100 mass% of the biodegradable resin composition, 0.2 mass% or more and less than 1.0 mass% of a carbodiimide compound, and 5.0 mass% or more and 40 mass% or less of a plate-like filler, and has melt tension at 160°C of 45 mN or more and 70 mN or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biodegradable resin composition suitable for molding, for example, seedling pots, and a molded article thereof. [Background technology]

[0002] Seeds of vegetables, flowers, and trees are generally sown in seedling containers (also called seedling pots) and raised for a certain period of time, after which the seedlings are removed from the pots and planted in a planting area for cultivation. Seedling pots are mainly made of resin such as polyethylene, and although used seedling pots can be reused after cleaning and disinfection, most are collected and then incinerated. Moreover, they have sometimes been released into the general environment without being properly collected after use.

[0003] In order to reduce the cost of disposing of used seedling pots and the labor required for their collection, as well as to take into account today's environmental concerns, there is a trend toward switching to seedling pots made of biodegradable resin, which do not require incineration. Biodegradable resin is a resin that is decomposed over a certain period of time by microorganisms in the soil and water of nature, ultimately breaking down into water and carbon dioxide. By using seedling pots made of biodegradable resin, seedlings can be planted in the ground without having to be removed from the pot. Because the seedling pots decompose in the ground, not only is collection and incineration unnecessary, but the planting process is also simplified.

[0004] For example, Patent Document 1 discloses a seedling container made of biodegradable resin. According to the invention of Patent Document 1, by providing a large number of holes, the container has the necessary strength during the seedling raising period above ground, and decomposition is promoted underground.

[0005] Such seedling pots are obtained by molding a resin composition by blow molding, vacuum molding, or the like, but these methods require a resin composition with high melt tension to be molded into a deep shape like a seedling pot. However, biodegradable resins have lower melt tension than general-purpose plastics such as polyethylene, making them inferior in moldability, and improvements are needed.

[0006] For example, a known method for improving the molding processability of biodegradable resins is to chain-extend biodegradable polyester resins using a carbodiimide compound to increase their molecular weight (Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-204265 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-63111

[0008] However, it is known that the addition of a carbodiimide compound to a biodegradable resin inhibits hydrolysis. Seedling pots are required to have the necessary strength during the seedling raising period above ground and to be degradable in the ground after planting. However, if too much carbodiimide compound is added, the decomposition in the ground after planting becomes slow, making it difficult to achieve both moldability and the degradability required for seedling pots. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, an object of the present invention is to provide a biodegradable resin composition and a molded article that are both moldable and degradable. [Means for solving the problem]

[0010] As a result of intensive research conducted by the present inventors to achieve the above-mentioned object, they discovered that by incorporating specific amounts of a carbodiimide compound and a plate-like filler as additives, a biodegradable resin composition that combines moldability and degradability can be obtained, and thus arrived at the present invention.

[0011] That is, the biodegradable resin composition of the present invention contains a biodegradable polyester resin and an additive, and contains 70% by mass or more and 100% by mass or less of polybutylene succinate adipate (PBSA), 0% by mass or more and 30% by mass or less of polybutylene succinate (PBS), and 0% by mass or more and 30% by mass or less of polybutylene adipate terephthalate (PBAT) relative to 100% by mass of the biodegradable polyester resin, The additives include a carbodiimide compound in an amount of 0.2% by mass or more and less than 1.0% by mass and a flake-like filler in an amount of 5.0% by mass or more and 40% by mass or less, relative to 100% by mass of the biodegradable resin composition; The melt tension at 160°C is 45 mN or more and 70 mN or less.

[0012] The present invention also relates to a molded article obtained by blow molding or vacuum molding the biodegradable resin composition. [Effects of the Invention]

[0013] The present invention can provide a biodegradable resin composition and a molded article that have both moldability and degradability. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating a seedling pot (type A) formed by blow molding. [Figure 2] FIG. 1 is a diagram illustrating a seedling pot (type B) formed by vacuum molding. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention is a biodegradable resin composition containing a biodegradable polyester resin and an additive. Biodegradable polyester resins include polybutylene succinate adipate (PBSA), polybutylene succinate (PBS), or polybutylene adipate terephthalate (PBAT). Specifically, PBSA is essential as a biodegradable polyester, and PBS or PBAT is also included.

[0016] In the present invention, PBSA is an aliphatic polyester resin, which is a polymerized condensation product of butanediol, an aliphatic diol, succinic acid, an aliphatic dicarboxylic acid, and adipic acid or adipic anhydride.

[0017] In the present invention, PBS is an aliphatic polyester resin, which is a polymerized condensation product of butanediol, an aliphatic diol, and succinic acid, an aliphatic dicarboxylic acid.

[0018] In the present invention, PBAT is an aliphatic-aromatic polyester resin, which is a polymerized condensation product of butanediol, an aliphatic diol, adipic acid or adipic anhydride, an aliphatic dicarboxylic acid, and terephthalic acid, an aromatic dicarboxylic acid.

[0019] The content of PBSA in 100% by mass of the biodegradable polyester resin of the present invention is 70% by mass or more and 100% by mass or less, and preferably 80% by mass or more and 90% by mass or less. PBSA is a biodegradable resin that decomposes faster than PBS or PBAT, and if the content is less than 70% by mass, it is difficult to achieve the decomposition rate required by the present invention.

[0020] When the biodegradable polyester resin of the present invention contains PBSA and PBS, the content of PBS is 0% by mass or more and 30% by mass or less, and preferably 10% by mass or more and 20% by mass or less, relative to 100% by mass of the biodegradable polyester resin. The combined use of PBSA and PBS improves moldability and also improves the crystallization temperature (described later) and the imprintability. However, if the PBS content exceeds 30% by mass, it is difficult to obtain the degradability required by the present invention.

[0021] When the biodegradable polyester resin of the present invention contains PBSA and PBAT, the PBAT content is 0% by mass or more and 30% by mass or less, and preferably 10% by mass or more and 20% by mass or less, relative to 100% by mass of the biodegradable polyester resin. The combined use of PBSA and PBAT improves molding processability, but if the PBAT content exceeds 30% by mass, deburring properties tend to deteriorate, making it difficult to achieve the degradability required by the present invention. Here, burr removal property refers to the ease with which burrs, which are resin that has solidified and protruded from the shape of the molded product, can be removed from the molded product. In the present invention, when two sets of seedling pots 1 having the shape shown in FIG. 1 are continuously produced using a blow molding machine, the seedling pots are obtained with the bottom surfaces connected by burrs, and the ease with which the burrs can be removed from the seedling pots refers to the ease with which the burrs can be removed from the seedling pots. In the present invention, a seedling pot is considered to have excellent burr removal property if the burrs can be removed from the seedling pot by manually twisting it one to three times.

[0022] The biodegradable resin composition of the present invention may contain other known biodegradable resins to the extent that the effects of the present invention are not impaired.

[0023] Next, the additive of the present invention will be described. The additive of the present invention includes a carbodiimide compound and a flake-like filler.

[0024] A carbodiimide compound is a polymer having a carbodiimide group in the molecule, and is reactive with the terminal carboxyl and hydroxyl groups of a biodegradable polyester resin. By reacting two or more molecules of a biodegradable polyester resin with a carbodiimide compound to extend the chain, the molecular weight of the biodegradable polyester resin can be increased and the melt tension of the biodegradable resin composition can be increased. Here, melt tension refers to the tension generated when a heated and molten resin is stretched, and is an indicator of moldability, as described below. Furthermore, carbodiimide compounds are known to suppress the hydrolysis of biodegradable polyester resins, so if too much carbodiimide compound is added, it may be difficult to achieve the degradability required by the present invention, and the screw load may be increased during molding, making it difficult to mix the materials, and even making molding impossible.

[0025] On the other hand, plate-like fillers are used as additives for biodegradable resin compositions, for example, as inorganic fillers or crystal nucleating agents. Adding a plate-like filler to a biodegradable resin composition can also increase its melt tension. However, adding too much plate-like filler can impose a screw load during molding, making it difficult to mix the materials and making molding impossible. Furthermore, the hardness of the resulting molded body increases, tending to deteriorate deburring properties.

[0026] In the present invention, by using a carbodiimide compound and a flake-like filler in combination, it is possible to provide a biodegradable resin composition and a molded article that have both moldability and degradability.

[0027] The carbodiimide compound used in the present invention may be any known compound, and is not particularly limited. Examples include monocarbodiimide compounds having one carbodiimide group in the same molecule, and polycarbodiimide compounds having two or more carbodiimide groups in the same molecule. Further examples include aromatic monocarbodiimide compounds and aromatic polycarbodiimide compounds having an aromatic ring in the molecule, and aliphatic monocarbodiimide compounds and aliphatic polycarbodiimide compounds not having an aromatic ring in the molecule. Of these, one type may be used alone, or two or more types may be used in combination. Among these, aliphatic monocarbodiimide compounds and aliphatic polycarbodiimide compounds are preferably used.

[0028] Examples of aliphatic monocarbodiimide compounds include dicyclohexylcarbodiimide, ethylene bis(dicyclohexylcarbodiimide), hexamethylene bis(dicyclohexylcarbodiimide), diisopropylcarbodiimide, N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide, etc. Aliphatic polycarbodiimide compounds can be synthesized by a decarboxylation condensation reaction of a diisocyanate using a carbodiimidization catalyst such as an organic phosphorus compound or an organic metal compound, and examples of such diisocyanates include hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, xylylene diisocyanate, tetramethylxylylene diisocyanate, etc. The carbodiimide compound of the present invention is preferably poly(4,4'-dicyclohexylmethane carbodiimide).

[0029] The flake filler in the present invention may be any known filler, and is not particularly limited. Examples include talc, kaolin, mica, clay, glass flakes, boron nitride, plate-like iron oxide, plate-like calcium carbonate, and plate-like aluminum hydroxide, with talc being preferred. Surface-treated flake fillers may also be used. Furthermore, a flake-like filler having an average particle size of 2 to 6 μm is preferred in terms of increasing the melt tension.

[0030] The content of the carbodiimide compound in 100% by mass of the biodegradable resin composition is 0.2% by mass or more but less than 1.0% by mass, preferably 0.3% by mass or more but less than 0.7% by mass. If the content is less than 0.2% by mass, the molecular weight does not increase sufficiently, resulting in low melt tension and poor moldability for deep shapes such as seedling pots. If the content is 1.0% by mass or more, no further increase in melt tension is observed, which places a load on the screw during molding, making it difficult to mix the materials and potentially making molding impossible. In addition, hydrolysis is suppressed, making it difficult to achieve the degradability required by the present invention.

[0031] The content of the platy filler in the biodegradable resin composition (100% by mass) is 5% to 40% by mass, preferably 7% to 25% by mass. If the content is less than 5% by mass, the thickening effect is insufficient, the melt tension is low, and the molding processability for deep shapes such as seedling pots tends to be poor. If the content is more than 40% by mass, the melt tension does not increase any further, and the screw load is applied during molding, making it difficult to mix the materials, and molding may become impossible.

[0032] In addition to the above, any additives may be added to the biodegradable resin composition of the present invention as long as they do not impair the effects of the present invention. Examples of such additives include plasticizers, heat stabilizers, lubricants, antiblocking agents, nucleating agents, biodegradation accelerators, biodegradation inhibitors, antioxidants, UV stabilizers, light stabilizers, antibacterial agents, fillers, colorants, antistatic agents, and starch. The additives used in the present invention are preferably those listed in the positive list of biomass plastics of the Japan Biomass Plastics Association.

[0033] The biodegradable resin composition of the present invention includes a dry blend obtained by mixing the above-mentioned biodegradable polyester resin of the present invention with additives, and a compound or masterbatch obtained by kneading the materials while heating them in a twin-screw extruder and granulating them by a strand cutting method.

[0034] The biodegradable resin composition of the present invention has a melt tension of 45 mN or more and 70 mN or less, and is excellent in moldability.

[0035] Here, the molding processability in the present invention will be explained. For example, known seedling pots include Type A, which has a general shape as shown in Figure 1, and Type B, which has a shape in which multiple pots are connected together as shown in Figure 2. Type A is mainly formed by blow molding, while Type B is mainly formed by vacuum forming a sheet. To form a deep shape like a seedling pot using these methods, a resin composition with high melt tension is required. The reason for this is that in blow molding, resin is extruded from above and sandwiched between molds on both sides, and then air is injected to expand it, continuously producing pairs of seedling pots. However, if drawdown occurs (a phenomenon in which the preformed resin cannot withstand its own weight and sags in the direction of gravity) due to the resin's low melt tension, differences in the weight of the pots are likely to occur. If the weight difference is large, the product will be defective. Furthermore, in vacuum molding, the sheet is softened by heating, and then vacuumed to adhere it to a mold to form a certain shape. However, if the resin has low melt tension and draws down, the pot will have poor appearance, such as wrinkles or uneven thickness.

[0036] The biodegradable resin composition of the present invention has a melt tension of 45 mN or more and 70 mN or less at 160°C, which suppresses drawdown during blow molding or vacuum molding, eliminates weight differences in the pots, and produces seedling pots with good appearance, i.e., has excellent moldability. If the melt tension is less than 45 mN, drawdown is large during blow molding or vacuum molding, and molding processability tends to be poor, while if it exceeds 70 mN, a screw load is applied during molding, making molding difficult. The method for measuring melt tension is shown in the examples.

[0037] The biodegradable resin composition of the present invention preferably has an MFR of 1.0 g / 10 min or more and 2.5 g / 10 min or less. MFR (melt flow rate) is a value that indicates the ease of flow of a resin. If the MFR is less than 1.0 g / 10 min, the viscosity of the resin is high, which puts a load on the screw during molding, making molding difficult. If the MFR is more than 2.5 g / 10 min, the drawdown during molding is large, which tends to result in poor moldability. The method for measuring MFR is shown in the examples.

[0038] The biodegradable resin composition of the present invention preferably has a crystallization temperature of 50°C or higher. The crystallization temperature is the temperature of the exothermic peak due to crystallization that appears when a resin is cooled at a constant rate from a molten state using DSC, and is an indicator of the temperature at which the resin cools and solidifies. The higher this temperature, the easier the resin solidifies. During resin molding, i.e., when the resin is heated and softened, it can be pressed against a mold to form imprints such as product names, manufacturer names, letters, symbols, and patterns. However, if the crystallization temperature is low, the imprints can be difficult to obtain. This is presumably because the resin takes time to cool and solidify, and is demolded in an incomplete state, making the imprints difficult to obtain. The crystallization temperatures of the biodegradable polyester resins of the present invention are approximately 30°C for PBSA, approximately 71°C for PBS, and approximately 39°C for PBAT. Therefore, in the present invention, if the crystallization temperature is 50°C or higher, it does not require a significant amount of time for cooling and solidifying, and the resin cools and solidifies between molding and demolding within the cycle time range of the molding machine, making the imprints more easily obtainable. Furthermore, if the crystallization temperature is 70° C. or higher, the markings are more likely to be formed clearly, which is more preferable. The method for measuring the crystallization temperature is as shown in the examples.

[0039] Next, the decomposability in the present invention will be explained. For example, seedling pots are required to have the necessary strength for the seedling raising period above ground and to be degradable underground after planting. Specifically, it is considered desirable for the pot to maintain sufficient strength for practical use for a maximum of four months of seedling raising, and to decompose by 80% or more of its mass before burial three months after burial (planting). In the present invention, a sheet made with a press is cut into a 4 cm diameter circle, and the resulting sample is buried in potting soil. It is then left to stand at a constant temperature and humidity of 25°C and 95% RH for three months. If the mass change rate when removed is 50% or more, it is determined that the strength during the seedling raising period is maintained and decomposition after burial is promoted. The method for measuring the mass change rate is shown in the Examples.

[0040] The biodegradable resin composition of the present invention is ideal for molding into deep shapes such as seedling pots, and can also be used for other purposes such as trays and various containers. [Example]

[0041] The present invention will be described in more detail below with reference to examples, but is not limited to these examples.

[0042] Examples 1 to 12, Comparative Examples 1 to 6 The components were blended in the blending ratios shown in Tables 1 to 3 below, kneaded, and mixed at 150°C using a twin-screw extruder, and granulated by a strand cut method to obtain compounds. The resulting compounds were evaluated for melt tension, MFR, crystallization temperature, biodegradability, moldability, stampability, and deburring properties, and the results are shown in Tables 1 to 3. However, in Comparative Examples 4 and 6, screw load was applied during molding, making sheet film formation and blow molding impossible, so moldability, stampability, and deburring properties could not be evaluated. The blending ratios in the tables are shown in mass%.

[0043] [Ingredients in Tables 1 to 3] Biodegradable polyester resin PBSA: Polybutylene succinate adipate (Mitsubishi Chemical Corporation, product name "Bio PBS FD92PB") PBS: Polybutylene succinate (Mitsubishi Chemical Corporation, product name "Bio PBS FZ91PB") PBAT: Polybutylene adipate terephthalate (BASF, product name "ecoflex (registered trademark) C1200") Additive 1: Talc (Takehara Chemical Industry Co., Ltd., product name "Hytron") Additive 2: Carbodiimide compound (Manufactured by Nisshinbo Chemical Co., Ltd., product name "Carbodilite LA-1")

[0044] [Melt tension] Using a capillary rheometer (manufactured by Toyo Seiki Seisakusho, trade name "PM-C"), the melt tension (mN) was measured under conditions of a temperature of 160°C, a piston descending speed of 10 m / min, and a take-up speed of 20 mm / min, and evaluated based on the following criteria. <Evaluation criteria> ×: Less than 45 mN 〇:45mN or more and 70mN or less ××: More than 70mN

[0045] [MFR] The MFR (g / 10 min) was measured using a melt indexer (manufactured by Toyo Seiki Seisakusho, trade name "F-F01") under conditions of a load of 2.16 kg and a temperature of 190°C, and evaluated based on the following criteria. <Evaluation criteria> ×: Less than 1.0g / 10min 〇: 1.0g / 10min or more and 2.5g / 10min or less ××: More than 2.5g / 10min

[0046] [Crystallization temperature] DSC measurements were performed using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Corporation, product name "DSC7020"), and the crystallization temperature (°C), which is the temperature of the exothermic peak due to crystallization that appears when the resin is cooled from a molten state, was determined from the DSC curve obtained under the condition of a temperature decrease rate of 10°C / min, and was evaluated based on the following criteria. <Evaluation criteria> ◎: 70℃ or higher 〇: 50℃ or higher but lower than 70℃ ×: Less than 50℃

[0047] [Biodegradable] A 0.3 mm thick sheet was prepared using a press and cut into a 4 cm diameter circle to prepare a sample. 20 g of potting soil (manufactured by Takii Seed Co., Ltd., product name "Planter's Soil") was weighed out and placed in a plastic petri dish (90 mm diameter), and the sample was buried therein. The moisture content of the potting soil was adjusted to approximately 55-65 mass% by adding ion-exchange water. The petri dish was left to stand at a constant temperature and humidity of 25°C and 95% RH. The mass of each test piece was measured before and after the test, and the mass change rate (%) after 3 months was calculated using the following formula (Equation 1). Mass change rate (%) = 100 × (mass of test piece before test - mass of test piece after test) / mass of test piece before test (Equation 1) <Evaluation criteria> 〇: 50% or more ×: Less than 50%

[0048] [Molding processability: Blow molding] Using a blow molding machine, two sets of two seedling pots 1 (Type A; thickness 0.2 mm, height 8.0 cm, base diameter 6.5 cm, opening diameter 9.0 cm, estimated mass 5.5 g) having the shape shown in Figure 1 were molded in succession. The processing temperature was 160°C. The resulting seedling pots were cut into individual pieces to obtain a total of four pots, and the mass of each pot was measured and evaluated based on the following criteria. <Evaluation criteria> 〇: No drawdown occurs during molding, and the mass of all four pieces is between 5.2g and 5.9g. ×: Drawdown occurred during molding, and there was one or more pots weighing less than 5.2 g or more than 5.9 g.

[0049] [Moldability: Vacuum forming] A sheet having a thickness of 0.45 mm was formed using an extrusion molding machine. The sheet temperature was then adjusted to approximately 100°C using a vacuum molding machine, and the sheet was molded into seedling pots 10 (Type B; length 70 cm, width 55 cm, number of pots 48) having the shape shown in Figure 2. The seedling pots obtained were visually observed and evaluated based on the following criteria. <Evaluation criteria> 〇: There is no drawdown during molding, no wrinkles or uneven thickness are seen overall, and it can be molded into a shape that conforms to the mold. ×: Large drawdown during molding, noticeable defects in appearance such as wrinkles and uneven thickness throughout, or molding not possible

[0050] [Engraving property] Using a blow molding machine, two sets of two seedling pots 1 (Type A; thickness 0.2 mm, height 8.0 cm, bottom diameter 6.5 cm, opening diameter 9.0 cm, assumed mass 5.5 g) having the shape shown in Figure 1 were produced in succession. Each of the resulting seedling pots was cut into pieces to obtain a total of four pots, and the mark 3 on each pot was visually observed and evaluated based on the following criteria. <Evaluation criteria> ◎: All four pots have detailed engravings 〇: There is some crushing of the engraving in the details, but most of the engraving is visible. ×: No markings on one or more pots

[0051] [Deburring] Using a blow molding machine, two sets of seedling pots (Type A; thickness 0.2 mm, height 8.0 cm, bottom diameter 6.5 cm, opening diameter 9.0 cm, assumed mass 5.5 g) having the shape shown in Figure 1 were produced in succession. The seedling pots were obtained with their bottoms connected by a burr. The ease of manually removing the burr from the seedling pot (burr removal property) was evaluated based on the following criteria. In the present invention, the ability to manually remove the burr from the seedling pot by twisting it one to three times is taken as an indication that the burr can be automatically removed using a device. <Evaluation criteria> ◎: The burr can be manually removed from the seedling pot with one twist. 〇: The burrs can be manually removed from the seedling pot by twisting them two or three times. ×: The burr cannot be removed from the seedling pot even after twisting it four times by hand.

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] Tables 1 and 2 show that in Examples 1 to 12 of the present invention, biodegradable resin compositions and molded articles having both moldability and degradability can be obtained. [Explanation of symbols]

[0056] 1 Seedling pot (Type A) 2 Bottom hole 3 Engraving 10 Seedling pot (Type B)

Claims

1. A biodegradable resin composition comprising a biodegradable polyester resin and an additive, With respect to 100% by mass of the biodegradable polyester resin, 70% by mass or more and 100% by mass or less of polybutylene succinate adipate, Polybutylene succinate: 0% by mass or more and 30% by mass or less; Contains 0% by mass or more and 30% by mass or less of polybutylene adipate terephthalate, The additives include a carbodiimide compound in an amount of 0.2% by mass or more and less than 1.0% by mass and a flake-like filler in an amount of 5.0% by mass or more and 40% by mass or less, relative to 100% by mass of the biodegradable resin composition; The biodegradable resin composition is characterized by having a melt tension of 45 mN or more and 70 mN or less at 160°C.

2. A molded article obtained by blow molding or vacuum molding the biodegradable resin composition according to claim 1.

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