Poly (3-hydroxybutyrate)-based resin sheet for thermoforming, molded article thereof, and method for producing same

Abstract

The present invention relates to a resin sheet for thermoforming, which contains a poly (3-hydroxybutyrate)-based resin. The difference between the melting point peak temperature of the poly (3-hydroxybutyrate)-based resin in differential scanning calorimetry and the end temperature on the high-temperature side of the melting point peak is 10 DEG C or more, and the thickness of the sheet is 0.15-1 mm. It is preferable that the melt viscosity of the poly (3-hydroxybutyrate)-based resin at 160 DEG C is 10,000 poise or more.

Description

[0001] This application is a divisional application of the Chinese invention application "Poly(3-hydroxybutyrate)-based thermoforming resin sheet, its molded body, and manufacturing method" with an application date of February 26, 2020 and application number 202080021612.2. Technical Field

[0002] The present invention relates to a poly(3-hydroxybutyrate)-based thermoforming resin sheet, a molded product thereof, and a production method thereof. Background Art

[0003] In recent years, the separation and recycling of household waste and composting are being carried out, mainly in Europe, and a plastic product that can be composted together with household waste is desired. As an example of such a plastic product, Patent Document 1 discloses a processed product obtained by thermoforming a sheet containing a polylactic acid polymer.

[0004] On the other hand, environmental issues caused by discarded plastics have attracted attention, especially large amounts of plastics that are dumped in the oceans or flow into the seas through rivers, etc., drifting in the oceans around the world. Such plastics retain their shape for a long time, and therefore can cause so-called ghost fishing, which can bind and capture marine organisms, and can affect the ecosystem by remaining in the digestive organs of marine organisms when ingested, causing feeding disorders.

[0005] In addition, the following problem is pointed out: microplastics, which are formed by the disintegration and micro-particleization of plastics due to ultraviolet rays, absorb harmful compounds in seawater, and these harmful compounds are ingested by marine organisms, thereby introducing harmful substances into the food chain.

[0006] In response to such marine pollution caused by plastics, the use of biodegradable plastics is expected. However, a report compiled by the United Nations Environment Programme in 2015 (Non-Patent Document 1) pointed out that plastics that can be biodegraded by composting, such as polylactic acid, cannot be expected to decompose in a short period of time in the actual ocean with low temperatures, and therefore cannot serve as a countermeasure to marine pollution.

[0007] Under such circumstances, poly(3-hydroxybutyrate)-based resins are biodegradable materials even in seawater, and therefore have attracted attention as raw materials for solving the above-mentioned problems.

[0008] Patent Document 2 describes a polyester resin composition containing two types of polyhydroxyalkanoates. Examples of the molded article thereof include films and sheets, and also describes that a sheet having a thickness of 100 μm was produced.

[0009] On the other hand, it is known that a method of forming a resin sheet into a container having a concave portion in the center, such as a food container, by performing thermoforming such as vacuum forming on the resin sheet is known. Thermoforming is mentioned in the above-mentioned Patent Document 2, but there is no record of actually performing thermoforming, and no research on it is done at all.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Publication No. 2002-248677

[0013] Patent Document 2: International Publication No. 2015 / 146194

[0014] Non-patent literature

[0015] Non-patent literature 1: United Nations Environment Programme 2015, BIODEGRADABLE PLASTICS & MARINE LITTER Summary of the invention

[0016] Problems to be solved by the invention

[0017] The present inventors have found that when a sheet containing a poly(3-hydroxybutyrate)-based resin is thermoformed into a molded body such as a container having a deep concave portion, thin portions are locally produced, which is insufficient to provide a molded body with high strength, and the obtained molded body sometimes has poor appearance such as poor shaping and rough surface.

[0018] In view of the above-mentioned situation, an object of the present invention is to provide a poly(3-hydroxybutyrate)-based thermoforming resin sheet that can be rapidly decomposed even in seawater and can be thermoformed into a molded body having a relatively uniform thickness and good appearance.

[0019] Solutions to the problem

[0020] The present inventors conducted intensive studies to solve the above-mentioned problems and found that a sheet containing a poly(3-hydroxybutyrate)-based resin has a specific crystal melting behavior and a sheet with a given thickness can be rapidly decomposed in seawater, and even a molded body with a shape such as a deep recess can be thermoformed into a molded body with a relatively uniform thickness and good appearance, thereby completing the present invention.

[0021] That is, the present invention relates to a poly(3-hydroxybutyrate)-based thermoforming resin sheet, which contains a poly(3-hydroxybutyrate)-based resin, wherein the difference between the melting point peak temperature and the end temperature on the high temperature side of the melting point peak in differential scanning calorimetry of the poly(3-hydroxybutyrate)-based resin is 10°C or more, and the thickness of the sheet is 0.15 to 1 mm. In addition, the melt viscosity of the poly(3-hydroxybutyrate)-based resin at 160°C is preferably 10,000 poise or more. In addition, the poly(3-hydroxybutyrate)-based resin is preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0022] The present invention also relates to a method for producing the poly(3-hydroxybutyrate)-based thermoforming resin sheet, the method comprising: melting the poly(3-hydroxybutyrate)-based resin in an extruder and extruding the melt from a T-die to obtain a sheet.

[0023] The present invention also relates to a method for producing the poly(3-hydroxybutyrate)-based thermoforming resin sheet, the method comprising the step of melting the poly(3-hydroxybutyrate)-based resin between heating rolls to obtain a sheet.

[0024] In addition, the present invention also relates to a molded body, which is a molded body formed by molding the above-mentioned poly(3-hydroxybutyrate)-based thermoforming resin sheet by thermoforming; In addition, it also relates to a method for manufacturing a molded body, which comprises: preheating the above-mentioned poly(3-hydroxybutyrate)-based thermoforming resin sheet to a temperature between the melting point peak temperature of the above-mentioned poly(3-hydroxybutyrate)-based resin in differential scanning calorimetry and the end temperature on the high temperature side of the melting point peak, and then performing a molding step. Preferably, the above-mentioned molding is performed by a vacuum molding method, a pressure molding method, or a vacuum pressure molding method.

[0025] Effects of the Invention

[0026] According to the present invention, there can be provided a poly(3-hydroxybutyrate)-based thermoforming resin sheet that can be rapidly decomposed even in seawater and can be thermoformed into a molded body having a relatively uniform thickness and good appearance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 These are a plan view and a longitudinal view showing the shape of a mold used when performing thermoforming in Examples and Comparative Examples. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0029] The poly(3-hydroxybutyrate) resin in the present invention refers to an aliphatic polyester resin that can be produced by microorganisms, and is a polyester resin having 3-hydroxybutyrate as a repeating unit. The poly(3-hydroxybutyrate) resin may be a poly(3-hydroxybutyrate) having only 3-hydroxybutyrate as a repeating unit, or a copolymer of 3-hydroxybutyrate and other hydroxyalkanoates. In addition, the poly(3-hydroxybutyrate) resin may be a mixture of a homopolymer and one or more copolymers, or a mixture of two or more copolymers.

[0030] Specific examples of the poly(3-hydroxybutyrate)-based resin include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Among them, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred because they are easy to produce industrially.

[0031] In addition, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoint that the melting point and crystallinity can be changed by changing the composition ratio of the repeating units, and the physical properties such as Young's modulus and heat resistance can be changed, and physical properties between polypropylene and polyethylene can be imparted, and it is easy to produce industrially as described above, and it is a plastic useful in terms of physical properties. In particular, among poly(3-hydroxybutyrate)-based resins having the characteristic of being easily thermally decomposed when heated to 180° C. or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is also preferred from the viewpoint that the melting point can be lowered and molding processing can be performed at low temperatures.

[0032] Regarding the composition ratio of the repeating units of the poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), the composition ratio of 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit is preferably 80 / 20 to 99 / 1 (mol / mol), and more preferably 75 / 15 to 97 / 3 (mol / mol) from the viewpoint of the balance between flexibility and strength. The reason for this is that it is preferably 99 / 1 or less from the perspective of flexibility, and is preferably 80 / 20 or more from the perspective of the resin having a moderate hardness.

[0033] Examples of commercially available products of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) include "KANEKA Biodegradable Polymer PHBH" (registered trademark) manufactured by KANEKA Corporation.

[0034] The melting point, Young's modulus, etc. of the above-mentioned poly(3-hydroxybutyrate-co-3-hydroxyvalerate) vary depending on the ratio of the 3-hydroxybutyrate component to the 3-hydroxyvalerate component. Since the two components are co-crystallized, the crystallinity is as high as 50% or more, and it is softer than poly(3-hydroxybutyrate), but the improvement of brittleness is insufficient.

[0035] Generally speaking, when a resin sheet is formed into a molded body such as a container, thermoforming is applied to shape the preheated sheet using a mold. Such thermoforming is implemented by the following method: the ends of the sheet are fixed with clips and pins, and the sheet is preheated and softened using a far-infrared heater, and then the sheet is molded along the mold by vacuum, compressed air, or a combination of vacuum and compressed air. In such molding, if the preheating is insufficient, the sheet cannot be fully molded along the mold, and it will become a molded body with poor so-called shaping properties. However, if the tension of the softened resin is excessively reduced when preheating is fully performed, especially in the case of thermoforming into a molded body such as a container with a deep concave portion that becomes larger when stretched, a thin portion will be locally produced, and therefore, there will be a problem of impaired strength of the molded body.

[0036] In order to impart excellent thermoformability, in the present invention, as a poly(3-hydroxybutyrate)-based resin, a poly(3-hydroxybutyrate)-based resin having a difference of 10°C or more between the melting point peak temperature in differential scanning calorimetry and the end temperature on the high temperature side of the melting point peak is used. This is because when the temperature difference is 10°C or more, it is easy to melt the poly(3-hydroxybutyrate)-based resin while leaving a portion of the crystals unmelted. Thus, when the sheet is thermoformed, while being sufficiently preheated for shaping of the sheet, a uniform elongation can be achieved during shaping by the tension maintained by the remaining crystals. Therefore, by thermoforming the sheet, a molded body with a relatively uniform thickness can be provided.

[0037] The temperature difference is more preferably 12° C. or more, further preferably 15° C. or more, and further preferably 18° C. or more. The upper limit of the temperature difference is 70° C. or less, and from the viewpoint of ease of production of the poly(3-hydroxybutyrate)-based resin, it is preferably 50° C. or less, more preferably 40° C. or less, further preferably 35° C. or less, and further preferably 30° C. or less.

[0038] In the present invention, the melting point peak temperature and the end temperature of the high temperature side of the melting point peak in differential scanning calorimetry are defined as follows. 4 to 10 mg of a resin sample is filled in an aluminum pan, and a differential scanning calorimeter is used to heat the sample from 30°C to 180°C at a rate of 10°C / min in a nitrogen gas flow to melt the resin sample. In the endothermic curve obtained at this time, the temperature at which the endothermic amount is the maximum is set as the melting point peak temperature, and the temperature at which the melting point peak ends closer to the high temperature side than the melting point peak temperature and no endothermic effect is confirmed is set as the end temperature of the high temperature side of the melting point peak. It should be noted that the above-mentioned melting point peak temperature and the end temperature of the high temperature side of the melting point peak are measured for the poly(3-hydroxybutyrate)-based resin contained in the poly(3-hydroxybutyrate)-based resin sheet as a whole.

[0039] As the poly(3-hydroxybutyrate)-based resin having a temperature difference of 10°C or more between the melting point peak temperature and the end temperature on the high temperature side of the melting point peak, a poly(3-hydroxybutyrate)-based resin having a broad melting point peak and containing a high melting point component can be used. In addition, the poly(3-hydroxybutyrate)-based resin having a broad melting point peak and containing a high melting point component and another poly(3-hydroxybutyrate)-based resin having a different melting point characteristic from the above-mentioned resin can be used in combination.

[0040] A specific method for producing the poly(3-hydroxybutyrate)-based resin having a broad melting point peak and containing a high melting point component is described in, for example, International Publication No. 2015 / 146194.

[0041] In addition, the melt viscosity of the poly(3-hydroxybutyrate) resin of the present invention at 160°C is preferably 10,000 poise or more. In this way, by using a poly(3-hydroxybutyrate) resin with a high melt viscosity, the drooping phenomenon of the sheet due to its own weight can be reduced in the preheating process when the sheet of the present invention is thermoformed, thereby making it possible to produce a molded body with excellent appearance from a large area sheet. The above-mentioned melt viscosity is more preferably 11,000 poise or more, further preferably 12,000 poise or more, and further preferably 13,000 poise or more. The upper limit of the above-mentioned melt viscosity is not particularly limited, but is preferably 30,000 poise or less from the viewpoint of the surface smoothness of the sheet and preventing overload of the extruder and heating roller described later.

[0042] In the range that does not impair the effect of the present invention, other resins other than the poly(3-hydroxybutyrate)-based resin may be included in the poly(3-hydroxybutyrate)-based thermoforming resin sheet of the present invention. As such other resins, for example, aliphatic polyester resins such as polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and polylactic acid, aliphatic aromatic polyester resins such as polybutylene adipate terephthalate, polybutylene sebacate terephthalate, and polybutylene azelaic terephthalate, etc. may be cited. As other resins, only one type may be included, or two or more types may be included.

[0043] The content of the other resin is not particularly limited, but is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the poly(3-hydroxybutyrate)-based resin. The lower limit of the content of the other resin is not particularly limited, and may be 0 parts by weight.

[0044] In addition, within the scope of not damaging the effect of the present invention, the poly (3-hydroxybutyrate) system thermoforming resin sheet of the present invention can include an additive that can be used together with a poly (3-hydroxybutyrate) system resin. As such an additive, talc, calcium carbonate, mica, silica and other inorganic fillers, pigments, dyes and other colorants, activated carbon, zeolite and other odor absorbers, vanillin, dextrin and other spices, plasticizers, antioxidants, antioxidants, weathering improvers, ultraviolet absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, sliding improvers, etc. can be listed. As an additive, only one can be included, or more than two can be included. For the content of these additives, those skilled in the art can suitably set according to their purpose of use.

[0045] In addition, from the viewpoint of being easy to perform uniform preheating during thermoforming, being able to produce a molded body with a relatively uniform thickness and good appearance, and from the viewpoint of the rigidity and lightness of the obtained molded body, the thickness of the poly(3-hydroxybutyrate)-based thermoforming resin sheet of the present invention is 0.15 to 1 mm. When the thickness of the sheet is thinner than the above range, the molded body obtained by thermoforming the sheet will have poor appearance such as wrinkles and rough surface, and conversely, when it is thicker than the above range, it is difficult to obtain a molded body with a relatively uniform thickness and good appearance while performing sufficient preheating to the extent that it can be shaped. The thickness of the above sheet is preferably 0.16 to 0.8 mm, and more preferably 0.2 to 0.6 mm.

[0046] Next, a method for producing the poly(3-hydroxybutyrate)-based thermoforming resin sheet of the present invention will be described.

[0047] The poly(3-hydroxybutyrate)-based thermoforming resin sheet of the present invention can be produced, for example, by melt-kneading the poly(3-hydroxybutyrate)-based resin in an extruder, extruding the sheet from a T-die connected to the extruder outlet, and then cooling the sheet on a cooling roll or sandwiching the sheet between two cooling rolls.

[0048] The poly(3-hydroxybutyrate)-based thermoforming resin sheet of the present invention can be produced, for example, by melt-kneading the poly(3-hydroxybutyrate)-based resin between a plurality of heating rolls and then, for example, passing the mixture between one or more cooling rolls and pressing the mixture to obtain a sheet.

[0049] In general, poly(3-hydroxybutyrate)-based resins have a very slow crystallization rate compared to other crystalline resins such as polypropylene. Therefore, there is a tendency that the resin cannot be fully crystallized and solidified on the surface of the cooling roller and is easily adhered to the cooling roller. Therefore, in order to promote the crystallization of the poly(3-hydroxybutyrate)-based resin and achieve solidification in a short time, the temperature of the cooling roller is preferably 40 to 60°C.

[0050] The poly(3-hydroxybutyrate)-based thermoforming resin sheet of the present invention is used to be formed into a molded body such as a container by the thermoforming. The thermoforming can be implemented by forming the preheated and softened sheet along a mold using vacuum and / or pressure as described above. As specific examples of the above-mentioned thermoforming, vacuum forming, pressure forming, vacuum pressure forming, mold forming, plunger-assisted forming, TOM forming and the like can be cited. Vacuum forming, pressure forming, or vacuum pressure forming is preferred because of its simplicity and low mold cost.

[0051] A person skilled in the art can appropriately set the temperature of the sheet to be reached by the above-mentioned preheating, preferably a temperature between the melting point peak temperature of the above-mentioned poly(3-hydroxybutyrate)-based resin in differential scanning calorimetry and the end temperature on the high temperature side of the melting point peak. By preheating the sheet to such a temperature, the poly(3-hydroxybutyrate)-based resin is melted while a part of the crystals remain without melting, thereby achieving both sufficient preheating to a degree that allows shaping and uniform elongation due to the remaining crystals, and a molded body with a relatively uniform thickness can be produced.

[0052] It should be noted that there is no particular limitation on the device for preheating the sheet to the above temperature, and examples include far-infrared heaters, hot wire heaters, hot air heaters, etc. Among them, far-infrared heaters are preferred because they are easy to heat quickly and evenly in the device. When using a far-infrared heater, the temperature of the heater is generally set to be higher than the target sheet temperature, and the temperature of the sheet is controlled by the distance from the heater to the sheet and the preheating time. For example, a method in which a far-infrared heater set to 300 to 350°C is set at a distance of 10 to 50 cm from the sheet and heated for 5 to 30 seconds can be cited. A method in which an infrared non-contact thermometer is used to measure the actual temperature of the above sheet, a method in which a thermal label whose color changes according to the temperature is attached to the sheet and preheating conditions are set can be cited.

[0053] The molded body obtained by thermoforming the poly(3-hydroxybutyrate)-based thermoforming resin sheet of the present invention is not particularly limited, and examples thereof include: a container having a recessed portion in the center, a container having a compartment, a container having a folded portion around an opening, a lid having a recessed portion or a convex portion in the center, a lid having a curved or stepped structure at a part of an end portion or the entire periphery, and the like.

[0054] Example

[0055] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples at all.

[0056] (Resin materials used)

[0057] Resin raw material 1: Made by KANEKA, KANEKA biodegradable polymer PHBH TM 151C〔Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)〕

[0058] Resin raw material 2: Made by KANEKA, KANEKA biodegradable polymer PHBH TM X131A〔Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)〕

[0059] (Differential Scanning Calorimetry Evaluation)

[0060] 4 to 10 mg of a resin sample is placed in an aluminum pan and heated from 30°C to 180°C at a rate of 10°C / min in a nitrogen gas stream using a differential scanning calorimeter. The resin sample melts, and in the endothermic curve obtained at this time, the temperature at which the endothermic amount becomes maximum is set as the melting point peak temperature, and the temperature at which the melting point peak ends on the high temperature side of the melting point peak temperature but no endothermic effect is confirmed is set as the end temperature on the high temperature side of the melting point peak.

[0061] (Method for measuring melt viscosity)

[0062] An orifice with a diameter of 1 mm, a length of 10 mm and an inflow angle of 45° was installed, and 15 g of a resin sample was filled in a capillary rheometer (Capillograph, cylinder diameter 10 mm) heated to 160°C. After preheating for 5 minutes, the piston was lowered at a speed of 10 mm / min, and the melt viscosity at a shear speed of 122 / s was calculated based on the stress applied to the piston when the molten resin was extruded from the above-mentioned orifice.

[0063] (Evaluation of film thickness)

[0064] The thickness of the sheet was measured with a vernier caliper at three locations, namely, the end portions and the center portion in the sheet width direction, and the sheet thickness was calculated by taking the arithmetic average.

[0065] (Evaluation of the biodegradability of tablets in seawater)

[0066] 6L of seawater (collected from the harbor of Takasago City, Hyogo Prefecture) after removing foreign matter with a sieve with a mesh size of 80μ, 3g of ammonium chloride based on ASTM D-7081, and 0.6g of dipotassium phosphate were placed in a plastic container, and pieces cut into 50mm squares were added, and the weight retention rate after 3 months was calculated. It should be noted that the water temperature of the seawater was maintained at 23°C.

[0067] (Sheet Thermoforming Method)

[0068] The sheet was thermoformed using a vacuum forming machine. First, the sheet was fixed to a square mold frame with a side of 200 mm or 300 mm. After a thermal label was pasted in the center of the sheet, the sheet was preheated in a preheating chamber with a far-infrared heater set to 350°C until the display (preheating temperature) of the thermal label reached a given temperature. Next, the mold was pushed up from the bottom of the sheet to make contact with the sheet. Vacuum suction was performed from the hole provided at the bottom of the mold to form the sheet along the mold, thereby forming it into a container shape and demolding it to obtain a molded body. It should be noted that the mold used for this evaluation is a mold for a rounded container with an opening of 110 mm square and a depth of 35 mm. The bottom of the mold is 80 mm square and has a rounded shape of R=10 mm. The bottom and side wall also have a curved portion of R=10 mm. A schematic diagram of the shape of the mold is shown in Figure 1 .

[0069] (Evaluation of the Thermoformability of Sheets)

[0070] Since the bottom corner of the molded body obtained by the above-mentioned thermoforming is stretched to the maximum extent and the thickness is thinned, the bottom corner and the center of the flat part of the bottom of the container are cut off, and their respective thicknesses are measured with a vernier caliper. The thickness ratio is calculated by the following formula 1 and evaluated according to the following criteria.

[0071] Formula 1: Thickness ratio = (thickness of bottom corner) / (thickness of bottom plane)

[0072] ○: The thickness ratio is 0.5 or more

[0073] ×: The above thickness ratio is less than 0.5

[0074] (Evaluation of Molded Article)

[0075] The appearance of the molded body obtained by the above-mentioned thermoforming was observed and evaluated according to the following criteria.

[0076] ○: The molded product is in the mold shape and has no appearance defects such as wrinkles or surface roughness.

[0077] △: The molded body has some wrinkles

[0078] ×: The molded product has poor appearance such as poor shaping, wrinkles, and rough surface.

[0079] [Production of poly(3-hydroxybutyrate) resin particles]

[0080] Resin raw material 1 and resin raw material 2 were mixed in the mixing ratio shown in Table 1, and 1 part by weight of pentaerythritol was added to 100 parts by weight of the total of the two resin raw materials and dry-blended. The obtained resin material was put into a φ26 mm co-rotating twin-screw extruder with a barrel temperature and a die head temperature set at 150°C for extrusion, and the strands were solidified by passing through a water tank filled with hot water at 45°C, and cut by a pelletizer to obtain resin pellets 1, 2 and 4.

[0081] In addition, the resin material obtained in the same manner as above was put into the above-mentioned twin-screw extruder with the barrel temperature set at 190°C and the die temperature set at 150°C for extrusion, and the strands were solidified by passing through a water tank filled with hot water at 45°C, and cut by a pelletizer to obtain resin pellets 3.

[0082] Table 1 shows the production conditions and melting point characteristics of each resin pellet.

[0083] [Table 1]

[0084]

[0085] <Example 1>

[0086] Connect the T-die with a width of 500 mm The barrel temperature and die temperature of the single screw extruder were set to 160°C, and resin pellets 1 were added and extruded in the form of sheets. The sheets were sandwiched between two cooling rollers arranged under the T die, and the ends in the width direction were slit, thereby obtaining a sheet with a width of 310 mm and a thickness of 0.31 m. In the evaluation of the thermoforming of the sheet, a die frame with a side of 300 mm was used, and the sheet was preheated in a manner of a preheating temperature of 140°C, and thermoforming was performed. The evaluation results are shown in Table 2.

[0087] <Example 2>

[0088] A sheet was obtained in the same manner as in Example 1 except that the resin pellets used for processing were changed to the resin pellets 2, and the thermoforming evaluation of the sheet was performed. The evaluation results are shown in Table 2.

[0089] <Example 3>

[0090] The evaluation results are shown in Table 2.

[0091] <Example 4>

[0092] A sheet was obtained in the same manner as in Example 1 except that the resin pellets used for processing were changed to resin pellets 3 and the barrel temperature and die temperature of the extruder were set to 155° C. In the evaluation of thermoforming of the sheet, molding was performed using a die frame having a side of 200 mm in addition to a die frame having a side of 300 mm. The evaluation results are shown in Table 2.

[0093] <Example 5>

[0094] Two rolls with a diameter of 8 inches were used, the roll setting temperature was set to 145°C, the roll rotation speed was set to 20 rpm and 18 rpm, the resin pellets 2 were supplied to the rolls, and after being wound around the rolls, they were kneaded for 2 minutes, and then cut, sandwiched between two iron plates, and after cooling, cut into 310 mm squares, thereby obtaining a sheet with a thickness of 0.71 mm. In the evaluation of the thermoformability of the sheet, the preheating temperature of the sheet was changed to 150°C, and the same procedure as in Example 1 was performed. The evaluation results are shown in Table 2.

[0095] <Comparative Example 1>

[0096] A sheet was obtained in the same manner as in Example 1 except that the raw material used for processing was changed to polylactic acid (Ingeo 10361D manufactured by Nature Works) and the barrel temperature and die temperature of the extruder were set to 170°C. The thermoformability evaluation of the sheet was carried out in the same manner as in Example 1 except that the preheating temperature of the sheet was changed to 150°C. The evaluation results of the obtained sheet are shown in Table 2.

[0097] <Comparative Example 2>

[0098] A sheet was obtained in the same manner as in Example 1 except that the resin pellet 4 was used, and the thermoformability of the sheet was evaluated. The evaluation results are shown in Table 2.

[0099] <Comparative Example 3>

[0100] A sheet was obtained in the same manner as in Example 1 except that the resin pellet 2 was used and the screw rotation speed was adjusted so that the sheet thickness was 0.10 mm, and the thermoformability of the sheet was evaluated. The evaluation results are shown in Table 2.

[0101] <Comparative Example 4>

[0102] A sheet was obtained in the same manner as in Example 1 except that the resin pellet 2 was used and the sheet taking-up speed was adjusted to a sheet thickness of 1.13 mm. In the evaluation of the thermoforming of the sheet, the sheet was preheated at a preheating temperature of 150° C. and at a preheating temperature of 160° C., and the molding was performed. The evaluation results are shown in Table 2.

[0103]

[0104] It is found that the thermoforming resin sheets of Examples 1 to 5 and Comparative Examples 2 to 4 obtained using poly(3-hydroxybutyrate)-based resins biodegraded in seawater, whereas the sheet of Comparative Example 1 using polylactic acid did not biodegrade at all in seawater.

[0105] In addition, it is understood from each of the Examples and Comparative Examples that the thicker the poly(3-hydroxybutyrate)-based thermoforming resin sheet is, the slower the biodegradation in seawater is.

[0106] It can be seen that in the molded bodies obtained from the thermoforming resin sheets of Examples 1 to 5 in which the difference between the melting point peak temperature of the resin raw material used and the end temperature on the high temperature side of the melting point peak is 10°C or more, even in the bottom corner portion that is stretched to the greatest extent during thermoforming, the thickness is not extremely thin compared to other portions, and the molded bodies can be suitably used as containers. In addition, in each example, the appearance evaluation of the molded bodies is also good.

[0107] However, in Example 4 using a resin having a low melt viscosity of less than 10,000 poise, a molded product with good appearance was obtained in the thermoforming using a mold frame with a side of 200 mm, but when a larger mold frame with a side of 300 mm was used, the drawdown during preheating was relatively large, and some wrinkles were observed in the molded product. This shows that by using a poly(3-hydroxybutyrate)-based resin having a melt viscosity as high as 10,000 poise as in Examples 1, 2, 3, and 5, large-area thermoforming can be performed well.

[0108] On the other hand, in the thermoforming resin sheet of Comparative Example 2 in which the difference between the melting point peak temperature of the resin raw material used and the high temperature end temperature of the melting point peak was less than 10° C., the thickness of the bottom corner of the obtained molded body was significantly thinner than that of other parts.

[0109] In Comparative Example 3 in which the thickness of the thermoforming resin sheet was as thin as 0.10 mm, wrinkles were generated at the bottom corner portion where the thickness became the thinnest by molding during demolding, and a good molded product was not obtained.

[0110] On the other hand, in Comparative Example 4 in which the thickness of the thermoforming resin sheet is as thick as 1.13 mm, due to the thickness, even if the thermosensitive label attached to the surface is preheated to 150°C, the internal preheating is insufficient and sufficient shaping cannot be achieved. Moreover, if the preheating temperature is further increased to 160°C, the surface melts and rough areas are observed, making it difficult to achieve both appearance and thermoforming properties.

Claims

1. A method for producing a molded body, the method comprising: include: A step of preheating and softening a thermoforming resin sheet containing a poly(3-hydroxybutyrate)-based resin and then molding the sheet into a molded body along a mold. The poly(3-hydroxybutyrate)-based resin has a difference between a melting point peak temperature and a high temperature end temperature of the melting point peak in differential scanning calorimetry of 10° C. or more and 70° C. or less, The thickness of the sheet is 0.15 to 1 mm. During the preheating, the resin sheet is heated to a temperature between the melting point peak temperature of the poly(3-hydroxybutyrate)-based resin in differential scanning calorimetry and the end temperature on the high temperature side of the melting point peak.

2. The method for producing a molded body according to claim 1, in, The molded body is a molded body having a shape of a concave portion.

3. The method for producing a molded body according to claim 1 or 2, in, The preheating is performed using a far infrared heater.

4. The method for producing a molded product according to claim 1 or 2, in, The forming is performed by a vacuum forming method, a pressure air forming method, or a vacuum pressure air forming method.

5. The method for producing a molded body according to claim 1 or 2, in, The preheating melts the poly(3-hydroxybutyrate)-based resin while leaving some crystals unmelted.

6. The method for producing a molded product according to claim 1 or 2, in, The poly(3-hydroxybutyrate)-based resin has a melt viscosity of 10,000 poise or more at 160°C.

7. The method for producing a molded product according to claim 1 or 2, in, The poly(3-hydroxybutyrate)-based resin is a mixture of a homopolymer and one or more copolymers, or a mixture of two or more copolymers.

8. The method for producing a molded body according to claim 7, in, The copolymer is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

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