JP7564652B2 - Manufacturing method of molded body - Google Patents

Description

The present invention relates to a thermoforming resin sheet containing a poly(3-hydroxybutyrate)-based resin, a method for producing the same, and a method for producing a molded article from the resin sheet.

In recent years, the separate collection and composting of food waste has been promoted, mainly in Europe, and there is a demand for plastic products that can be composted together with food waste. As an example of such a plastic product, Patent Document 1 discloses a processed product made by thermoforming a sheet made of a polylactic acid-based polymer.

On the other hand, environmental problems caused by discarded plastics have been brought into the spotlight, and it has become clear that large amounts of plastic, particularly plastic that has been dumped in the ocean or has flowed into the ocean via rivers, are drifting in the oceans on a global scale. Because such plastics retain their shape for long periods of time, they have been pointed out to have an impact on the ecosystem, such as by binding and capturing marine organisms, a practice known as ghost fishing, and by being ingested by marine organisms, where the plastic remains in their digestive tracts and causes eating disorders.

Furthermore, it has been pointed out that microplastics, which are plastics that break down and break down into tiny particles due to ultraviolet rays, adsorb harmful compounds in seawater, and are then ingested by marine organisms, resulting in the incorporation of harmful substances into the food chain.

The use of biodegradable plastics is expected to combat marine pollution caused by this type of plastic, but a report compiled by the United Nations Environment Programme in 2015 pointed out that plastics that can be biodegraded through compost, such as polylactic acid, cannot be expected to decompose in a short period of time in the cold ocean temperatures, and therefore cannot be used to combat marine pollution.

In this situation, poly(3-hydroxybutyrate) resins are attracting attention as a material that can solve the above problems because they can biodegrade even in seawater.

Patent Document 2 describes a polyester resin composition containing two types of polyhydroxyalkanoates, and gives examples of molded products such as films and sheets, and describes the production of sheets with a thickness of 100 μm.

Patent document 3 describes a method of producing a film by melting a thermoplastic resin containing polyhydroxyalkanoate as a main component, forming it into a film, crystallizing it, and then rolling and first stretching the resin at a temperature below the melting point and above the glass transition temperature, and then secondly stretching the resin at a temperature higher than the rolling temperature.

On the other hand, there is a known method of subjecting a resin sheet to thermoforming such as vacuum forming to form it into a container with a central recess, such as a food container. The aforementioned Patent Document 2 mentions thermoforming, but does not state that thermoforming has actually been carried out, and does not consider at all the feasibility of thermoforming. Furthermore, Patent Document 3 does not state or suggest thermoforming itself.

JP 2002-248677 A International Publication No. 2015/146194 JP 2006-168159 A

The inventors have found that when a resin sheet containing a poly(3-hydroxybutyrate) resin is thermoformed into a molded article such as a container having a shape with deep recesses, there are some areas where the thickness is extremely thin, resulting in the molded article having insufficient strength.

In view of the above-mentioned current situation, the present invention aims to provide a resin sheet for thermoforming that contains a poly(3-hydroxybutyrate)-based resin and can be formed into a molded article having a relatively uniform thickness by thermoforming.

As a result of intensive research aimed at solving the above problems, the inventors discovered that by constructing a resin sheet containing a poly(3-hydroxybutyrate) resin so that the heat shrinkage rate measured by heating at a specific temperature is equal to or greater than a specific value, the resin sheet can be thermoformed into a molded article having a relatively uniform thickness, even if the molded article is a container or other shape that has a deep recess, and thus completed the present invention.

That is, the present invention relates to a thermoforming resin sheet containing a poly(3-hydroxybutyrate)-based resin, wherein the thermoforming resin sheet has a heat shrinkage rate of 2% or more in the MD direction and/or TD direction measured when heated to 160°C as the temperature exhibited by the thermoforming resin sheet.
Preferably, the poly(3-hydroxybutyrate)-based resin comprises poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).
Preferably, the thermoforming resin sheet further contains a filler, and the content of the filler is 1 to 100 parts by weight per 100 parts by weight of the poly(3-hydroxybutyrate)-based resin. Preferably, the filler is an inorganic filler, and more preferably, the inorganic filler contains at least one selected from silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, and carbon black. Also, preferably, the filler is an organic filler.
Preferably, the difference between the melting peak temperature and the end temperature on the higher temperature side of the melting peak in differential scanning calorimetry of the poly(3-hydroxybutyrate) resin is 10° C. or more and 70° C. or less.
Preferably, the thermoforming resin sheet has a thickness of 0.1 to 1 mm.
Preferably, the drawdown of the thermoforming resin sheet measured by the following method is 10 cm or less.
Drawdown: The thermoforming resin sheet, measuring 20 cm in MD x 20 cm in TD, is fixed on a frame measuring 20 cm in length x 20 cm in width x 50 cm in height with a square opening measuring 17.5 cm in length x 17.5 cm in width in the center, and the thermoforming resin sheet is heated to a temperature of 140°C. This is the vertical distance from the fixed surface of the thermoforming resin sheet to the lowest point.
The present invention also relates to a method for producing the thermoforming resin sheet, the method including the steps of melting a sheet raw material containing the poly(3-hydroxybutyrate)-based resin in an extruder and molding the melted sheet into a sheet, and stretching the molded sheet uniaxially or biaxially at a stretch ratio of 1.1 times or more to obtain a thermoforming resin sheet.
Preferably, the temperature of the sheet raw material containing the poly(3-hydroxybutyrate)-based resin is in the range of 40° C. or more and 165° C. or less from the time when the sheet raw material is melted in an extruder to the time when the sheet raw material is stretched to obtain the thermoforming resin sheet.
Preferably, the forming into the sheet is carried out by sandwiching the molten sheet material between two or more rolls.
Preferably, the forming into a sheet is carried out by extruding a molten sheet material through a T-die.
The present invention further relates to a method for producing a molded article, which comprises a step of preheating the resin sheet for thermoforming and then molding the same.
Preferably, the thermoforming resin sheet is preheated to a temperature between the melting peak temperature and the end temperature on the higher side of the melting peak in differential scanning calorimetry of the poly(3-hydroxybutyrate) resin.

According to the present invention, it is possible to provide a thermoforming resin sheet that contains a poly(3-hydroxybutyrate)-based resin and can be formed into a molded article having a relatively uniform thickness by thermoforming.

FIG. 1 shows a mold used when thermoforming was performed in the examples and comparative examples. FIG. 1 is a top view showing a resin sheet when measuring the heat shrinkage rate in Examples and Comparative Examples. FIG. 1 shows a frame used for measuring drawdown in the examples and comparative examples. FIG. 1 is a side view illustrating the drawdown measured in the examples and comparative examples.

The following describes an embodiment of the present invention, but the present invention is not limited to the following embodiment.

One embodiment of the present invention relates to a thermoforming resin sheet containing a poly(3-hydroxybutyrate)-based resin.
The poly(3-hydroxybutyrate)-based resin is an aliphatic polyester resin that can be produced from a microorganism, and is a polyester resin having 3-hydroxybutyrate as a repeating unit. The poly(3-hydroxybutyrate)-based resin may be a poly(3-hydroxybutyrate) having only 3-hydroxybutyrate as a repeating unit, or may be a copolymer of 3-hydroxybutyrate and another hydroxyalkanoate. The poly(3-hydroxybutyrate)-based resin may be a mixture of a homopolymer and one or two or more types of copolymers, or a mixture of two or more types of copolymers.

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 these, 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.

Furthermore, by changing the composition ratio of the repeating units, it is possible to change the melting point and degree of crystallinity, and thus physical properties such as Young's modulus and heat resistance, making it possible to impart physical properties between those of polypropylene and polyethylene. In addition, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoints that it is easy to produce industrially and is a physically useful plastic. In particular, among poly(3-hydroxybutyrate)-based resins that tend to decompose thermally when heated to 180°C or higher, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferred from the viewpoints that it can lower the melting point and enable molding and processing at low temperatures.

From the viewpoint of the balance between flexibility and strength, the composition ratio of the repeating units of the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is preferably 80/20 to 99/1 (mol/mol) in terms of the composition ratio of 3-hydroxybutyrate units/3-hydroxyhexanoate units, and more preferably 75/15 to 97/3 (mol/mol). This is because a ratio of 99/1 or less is preferable from the viewpoint of flexibility, and a ratio of 80/20 or more is preferable in order for the resin to have an appropriate hardness.

Commercially available products of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) include Kaneka Biodegradable Polymer PHBH (registered trademark) from Kaneka Corporation.

The melting point and Young's modulus of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) vary depending on the ratio of the 3-hydroxybutyrate and 3-hydroxyvalerate components, but because the two components co-crystallize, the degree of crystallinity is high at 50% or more, and although it is more flexible than poly(3-hydroxybutyrate), the improvement in brittleness is insufficient.

In general, thermoforming is used to mold a resin sheet into a molded product such as a container, by applying a mold to a preheated sheet. In this type of thermoforming, the sheet end is fixed with a clamp or pin, the sheet is preheated and softened using a far-infrared heater or the like, and then the sheet is fitted to the mold using vacuum or compressed air. In this type of molding, if the preheating is insufficient, the sheet cannot be fitted to the mold sufficiently, resulting in a molded product with poor moldability. However, if the tension of the softened resin is reduced too much when the resin is preheated sufficiently, when thermoforming into a molded product such as a container with deep recesses, there are areas where the thickness is extremely thin locally, especially in areas where the sheet is stretched significantly, which causes a problem of compromising the strength of the molded product.

In order to provide excellent thermoformability, the thermoforming resin sheet according to one embodiment of the present invention has a heat shrinkage ratio of 2% or more in the MD and/or TD directions of the resin sheet, measured by heating the resin sheet to 160°C, which is the temperature indicated by the resin sheet. The heat shrinkage ratio is a numerical value indicating the degree of shrinkage of the resin sheet when it is heated. If the heat shrinkage ratio is 2% or more, when the resin sheet is softened by heating, the resin sheet shrinks, suppressing drawdown, and preventing the resin sheet from stretching too much before shaping, resulting in uneven thickness. Therefore, it is possible to form a molded body with a relatively uniform thickness. Note that a thermoforming resin sheet that satisfies the heat shrinkage ratio can be manufactured by performing a process of stretching at a specific stretch ratio, as described below.

In general, the MD direction is also called the machine direction, flow direction, or length direction, and the TD direction is perpendicular to the MD direction and is also called the perpendicular direction or width direction. In one embodiment of the present invention, only the heat shrinkage rate in the MD direction may satisfy the numerical range, or only the heat shrinkage rate in the TD direction may satisfy the numerical range, or the heat shrinkage rates in both the MD and TD directions may satisfy the numerical range.

The heat shrinkage rate is preferably 3% or more, more preferably 5% or more, and even more preferably 6% or more. There is no particular upper limit to the heat shrinkage rate, but from the viewpoint of ease of thermoforming, it is preferably 90% or less, more preferably 70% or less, even more preferably 50% or less, even more preferably 30% or less, and particularly preferably 20% or less.

The heat shrinkage is measured as follows. As shown in Fig. 2, a resin sheet is cut to a size of 120 mm in the MD direction x 120 mm in the TD direction, and a square of 100 mm in the MD direction x 100 mm in the TD direction is marked in the center. The resin sheet is placed on a paper coated with silica, heated in a dryer set at 160°C for 10 minutes, and then cooled to room temperature. The length of the sides of the square in the MD direction and/or TD direction is measured, and the heat shrinkage is calculated by Equation 1.
Formula 1: Heat shrinkage rate = ((length before heating (mm)) - (length after heating (mm))) / (length before heating (mm)) x 100

In one embodiment of the present invention, in order to impart superior thermoformability, it is preferable to use a poly(3-hydroxybutyrate) resin in which the difference between the melting peak temperature in differential scanning calorimetry and the end temperature on the higher temperature side of the melting peak is 10°C or more and 70°C or less. This is because when the temperature difference is 10°C or more, it is easy to melt the poly(3-hydroxybutyrate) resin while leaving some of the crystals unmelted. This makes it possible to achieve uniform elongation during molding by the tension held by the remaining crystals while preheating the sheet sufficiently to mold it. This makes it easy to provide a molded body with a relatively uniform thickness by thermoforming the sheet.

The temperature difference is more preferably 12°C or more, even more preferably 15°C or more, and even more 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 poly(3-hydroxybutyrate)-based resin, it is preferably 50°C or less, more preferably 40°C or less, even more preferably 35°C or less, and even more preferably 30°C or less.

The melting peak temperature and the end temperature on the higher temperature side of the melting peak in differential scanning calorimetry are measured as follows. 4 to 10 mg of a resin sample is filled into an aluminum pan, and the resin sample is melted by heating it from 30°C to 180°C at a rate of 10°C/min using a differential scanning calorimeter under a nitrogen stream. In the endothermic curve obtained, the temperature at which the amount of endothermic heat is maximum is taken as the melting peak temperature, and the temperature at which the melting peak ends and no endothermic heat is observed on the higher temperature side of the melting peak temperature is taken as the end temperature on the higher temperature side of the melting peak. The melting peak temperature and the end temperature on the higher temperature side of the melting peak are measured for the entire poly(3-hydroxybutyrate) resin contained in the thermoforming resin sheet.

As the poly(3-hydroxybutyrate)-based resin in which the temperature difference between the melting peak temperature and the end temperature on the higher side of the melting peak is 10°C or more, a poly(3-hydroxybutyrate)-based resin having a broad melting peak and containing a high melting component can be used. In addition, the poly(3-hydroxybutyrate)-based resin having a broad melting peak and containing a high melting component can be used in combination with another poly(3-hydroxybutyrate)-based resin having melting point characteristics different from that of the said resin.

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

The thermoforming resin sheet according to one embodiment of the present invention may not contain a filler, but preferably contains a filler. It is expected that the inclusion of a filler will suppress dimensional changes after thermoforming. The filler may be either an inorganic filler or an organic filler, or both may be used in combination. The inorganic filler is not particularly limited, but examples include silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, carbon black, etc. Only one type of inorganic filler may be used, or two or more types may be used in combination.

The content of the filler is preferably 1 to 100 parts by weight, more preferably 3 to 80 parts by weight, even more preferably 5 to 70 parts by weight, and even more preferably 10 to 60 parts by weight, per 100 parts by weight of the poly(3-hydroxybutyrate) resin.

The thermoforming resin sheet according to one embodiment of the present invention may contain other resins besides poly(3-hydroxybutyrate)-based resins, provided that the effects of the invention are not impaired. Examples of such other resins include aliphatic polyester-based resins such as polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and polylactic acid, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate, polybutylene sebate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

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, and even more preferably 10 parts by weight or less, per 100 parts by weight of the poly(3-hydroxybutyrate) resin. There is no particular lower limit to the content of the other resin, and it may be 0 parts by weight or more.

In addition, it is preferable that the thermoforming resin sheet according to one embodiment of the present invention does not contain an additive that bleeds out when the resin sheet is stored at 80°C or higher. International Publication No. 2015/052876 has revealed that a sample containing added pentaerythritol does not bleed out after storage for one month at 23°C and humidity of 50% or less, but there is a possibility that it may bleed out under storage conditions of 80°C or higher. Therefore, it is preferable that the thermoforming resin sheet according to one embodiment of the present invention does not contain pentaerythritol. In addition, even if the resin sheet does not contain a crystal nucleating agent such as pentaerythritol, it is possible to produce a thermoforming resin sheet with good productivity by adopting the manufacturing method described below.

The thermoforming resin sheet according to one embodiment of the present invention may contain additives that can be used with the poly(3-hydroxybutyrate) resin, provided that the effects of the invention are not impaired. Examples of such additives include colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolite, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather resistance improvers, UV absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding improvers. Only one type of additive may be contained, or two or more types may be contained. The content of these additives can be appropriately set by a person skilled in the art depending on the purpose of use.

The thickness of the thermoforming resin sheet according to one embodiment of the present invention is preferably 0.1 to 1 mm from the viewpoint of being able to perform uniform preheating in thermoforming, being able to produce a molded body having a relatively uniform thickness and good appearance, and from the viewpoint of the rigidity and lightness of the obtained molded body. If 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 surface roughness, and conversely, if the thickness is thicker, it will be difficult to perform sufficient preheating to the extent that it can be shaped, and at the same time, to obtain a molded body having a relatively uniform thickness and good appearance. The thickness of the sheet is preferably 0.15 to 0.8 mm, and more preferably 0.20 to 0.6 mm.

The thermoforming resin sheet according to one embodiment of the present invention preferably has a drawdown of 10 cm or less, measured by the following method. Drawdown is a value indicating the degree of sagging when a heated and softened resin sheet sags under its own weight. If the drawdown is 10 cm or less, it is possible to prevent the resin sheet from stretching too much during thermoforming from when it is softened to when it is shaped, resulting in uneven thickness. This makes it possible to form a molded product with a relatively uniform thickness. Note that a thermoforming resin sheet that satisfies the drawdown can be manufactured by performing a process of stretching at a specific stretch ratio, as described below.

The drawdown is more preferably 9 cm or less, and even more preferably 8 cm or less. There is no particular lower limit to the drawdown, but from the viewpoint of ease of thermoforming, it is preferably 1 cm or more, more preferably 2 cm or more, even more preferably 3 cm or more, and particularly preferably 4 cm or more.

Drawdown is measured as follows. A thermoforming resin sheet measuring 20 cm in MD and 20 cm in TD is fixed on a 20 cm long x 20 cm wide x 50 cm high frame with a square opening of 17.5 cm long x 17.5 cm wide in the center, and the drawdown is the vertical distance from the fixing surface to the lowest point of the thermoforming resin sheet when the thermoforming resin sheet is heated to 140°C. The lowest point refers to the lowest point when the resin sheet sags through the opening under its own weight due to softening caused by heating, as shown in Figure 4.

(Method for producing thermoforming resin sheet)
Next, a method for producing a thermoforming resin sheet according to one embodiment of the present invention will be described.

The method for producing a thermoforming resin sheet according to one embodiment of the present invention is not particularly limited, but the method includes a step of melting a sheet raw material containing the poly(3-hydroxybutyrate) resin in an extruder, forming it into a sheet, and a step of stretching the formed sheet uniaxially (MD or TD) or biaxially (MD and TD) at a stretch ratio of 1.1 times or more to obtain a thermoforming resin sheet.

Specifically, the forming into the sheet may be performed by sandwiching the molten sheet material between two or more rolls, i.e., by a calendar method, or by extruding the molten sheet material through a T-die, i.e., by an extrusion molding method. After forming into a sheet, the sheet may be cooled on one or more cooling rolls, or may be cooled by sandwiching it between two cooling rolls.

In general, poly(3-hydroxybutyrate) resins have an extremely slow crystallization rate compared to other crystalline resins such as polypropylene. As a result, they tend not to crystallize sufficiently on the surface of the cooling roll and tend to stick to the cooling roll. Therefore, it is preferable to adjust the temperature of the cooling roll to 40 to 100°C in order to advance the crystallization of the poly(3-hydroxybutyrate) resin to a certain extent and avoid sticking to the cooling roll.

During the process of cooling the sheet, it is preferable to carry out a step of stretching the sheet in the MD direction and/or TD direction by pulling the sheet in the MD direction with a difference in rotation speed between the rolls and/or by clamping the widthwise end of the sheet and pulling it in the TD direction. By carrying out this stretching step, when the obtained thermoforming resin sheet is heated, the stretched molecular chains shrink and the entire sheet shrinks significantly, so that a thermoforming resin sheet that satisfies the above-mentioned numerical range of the heat shrinkage rate can be obtained.

The stretching ratio in the stretching step is preferably 1.1 times or more, more preferably 1.2 times or more, even more preferably 1.3 times or more, and particularly preferably 1.4 times or more. There is no particular upper limit to the stretching ratio, but it is preferably 3.0 times or less, more preferably 2.5 times or less, and even more preferably 2.0 times or less.

It is preferable that the sheet-forming step and the stretching step are carried out continuously. Specifically, after the sheet-forming step, it is preferable to carry out the stretching step without carrying out a crystallization step (specifically, a step of quenching in ice water and then annealing at 40°C for 12 hours) as described in Patent Document 3.

That is, in one embodiment of the present invention, the poly(3-hydroxybutyrate)-based resin that is subjected to the stretching process is not completely crystallized. However, some crystals remain in the sheet without melting, and the resin crystals and molten material are mixed. By performing the stretching process on such a sheet, a thermoforming resin sheet that satisfies the above-mentioned numerical range of the heat shrinkage rate can be obtained, and the remaining crystals serve as the starting point for crystallization of the entire poly(3-hydroxybutyrate)-based resin during and after the stretching process, even without performing the above-mentioned troublesome crystallization process.

From the above viewpoints, it is preferable to set the manufacturing conditions so that the temperature of the sheet material containing the poly(3-hydroxybutyrate)-based resin is within the range of 40°C to 165°C from the time when the sheet material is melted in an extruder and then stretched to obtain the thermoforming resin sheet. If the temperature exceeds 165°C, the crystals in the poly(3-hydroxybutyrate)-based resin cannot be allowed to remain during the manufacturing process, and as a result, the crystallization of the poly(3-hydroxybutyrate)-based resin as a whole becomes difficult to proceed, and the productivity of the thermoforming resin sheet may decrease. If the temperature is less than 40°C, molding into a sheet shape or stretching to a predetermined ratio may not be performed sufficiently, and the obtained thermoforming resin sheet may not satisfy the above-mentioned numerical range of the heat shrinkage rate. The temperature is more preferably 40°C to 165°C, and even more preferably 60°C to 160°C.

(Method for producing molded body)
The thermoforming resin sheet according to one embodiment of the present invention is used for forming a molded body having concave and/or convex parts, such as a container, by thermoforming. As described above, thermoforming can be performed by aligning a preheated and softened sheet with a mold using vacuum or compressed air. Specific examples of the thermoforming include vacuum forming, compressed air forming, vacuum-pressure forming, matched mold forming, plug-assist forming, and TOM forming, among which vacuum forming and compressed air forming are preferred because they are simple and require low mold costs.

The temperature of the sheet achieved by the preheating can be set as appropriate by those skilled in the art, but is preferably a temperature between the melting point peak temperature and the end temperature on the higher side of the melting point peak in differential scanning calorimetry of the poly(3-hydroxybutyrate) resin. By preheating the sheet to such a temperature, most of the poly(3-hydroxybutyrate) resin is melted while at the same time leaving some crystals unmelted, which makes it possible to achieve both sufficient preheating to allow shaping and uniform elongation due to the remaining crystals, making it possible to produce a molded product with a relatively uniform thickness.

The device used to preheat the sheet to the above temperature is not particularly limited, and examples include far-infrared heaters, hot-wire heaters, and hot-air heaters. Among these, far-infrared heaters are preferred because they can heat the sheet quickly and uniformly. When using a far-infrared heater, the heater temperature is generally set higher than the target sheet temperature, and the sheet temperature is controlled by the distance between the heater and the sheet and the preheating time. For example, a far-infrared heater set to 300 to 350°C is placed at a distance of 10 to 50 cm from the sheet and heated for 5 to 30 seconds. The actual temperature of the sheet can be measured using a non-contact thermometer using infrared rays, or the preheating conditions can be set by attaching a Thermo Label (registered trademark) that changes color depending on the temperature to the sheet.

The molded product obtained by thermoforming the thermoforming resin sheet according to one embodiment of the present invention is not particularly limited, but examples include a container with a recess in the center, a container with a partition, a container with a folded portion around the opening, a lid, etc.

The following examples and comparative examples are presented to explain the present invention in more detail, but the present invention is not limited to these examples.

In the examples and comparative examples, the following raw materials were used.
(Poly(3-hydroxybutyrate)-based resin)
A-1: Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) obtained according to the method described in WO 2013/147139, having a 3-hydroxyhexanoate (3HH) composition of 11.2 mol% and a weight average molecular weight of 580,000 in terms of standard polystyrene measured by GPC.
A-2: P3HB3HH obtained according to the method described in WO 2008/010296, having a 3HH composition of 5.4 mol% and a weight average molecular weight of 620,000 in terms of standard polystyrene measured by GPC

In the examples and comparative examples, the following talc was used as the filler.
B-1: Microace K-1 (made by Nippon Talc)

(Differential Scanning Calorimetry Analysis Evaluation)
An aluminum pan was filled with 4 to 10 mg of a resin sample, and the resin sample was melted using a differential scanning calorimeter by heating from 30°C to 180°C at a rate of 10°C/min under a nitrogen stream. In the endothermic curve obtained when the resin sample was melted, the temperature at which the amount of endothermic heat was maximum was determined as the melting point peak temperature, and the temperature at which the melting point peak ended on the higher temperature side than the melting point peak temperature and no endothermic heat was observed was determined as the end temperature on the higher temperature side of the melting point peak.

(Evaluation of Resin Sheet Thickness)
The thickness was measured using a vernier caliper at 10 points spaced 10 cm apart along the TD direction of the resin sheet, and the arithmetic mean value of the thicknesses at the 10 points was calculated to obtain the thickness of the resin sheet.

(Evaluation of heat shrinkage rate)
As shown in Figure 2, the resin sheet was cut to a size of 120 mm in the MD direction x 120 mm in the TD direction, and a square mark of 100 mm in the MD direction x 100 mm in the TD direction was made in the center. The resin sheet was placed on a paper coated with silica, heated in a dryer set at 160°C for 10 minutes, and then cooled to room temperature. The length of the side of the square in the MD direction was measured, and the heat shrinkage rate was calculated using Equation 1.
Formula 1: Heat shrinkage rate = ((length before heating (mm)) - (length after heating (mm))) / (length before heating (mm)) x 100

(Drawdown evaluation)
A thermograph was attached to the center of a resin sheet measuring 20 cm in MD x 20 cm in TD, and the resin sheet was fixed on a frame measuring 20 cm in length x 20 cm in width x 50 cm in height with a square opening of 17.5 cm in length x 17.5 cm in width in the center. The frame was placed in an oven set at 160°C, and when the thermograph indicated 140°C, the frame 11 was removed. As shown in Figure 4, the vertical distance 13 from the fixed surface of the resin sheet to the lowest point 14 of the hanging resin sheet 12 was measured to evaluate drawdown.

(Method of Thermoforming Resin Sheet)
The resin sheet was thermoformed using a vacuum forming machine. First, the resin sheet was cut into a size of 300 mm on one side, fixed to a square mold, and a thermo label (registered trademark) was attached to the center of the resin sheet. In a preheating chamber in which a far-infrared heater was set to 350 ° C., the resin sheet was preheated until the indication of the thermo label (registered trademark) reached a predetermined temperature (preheating temperature). Next, a mold was pushed up from below the resin sheet, the mold was brought into contact with the resin sheet, and then a vacuum was drawn from a hole provided at the bottom of the mold. The resin sheet was molded into a container shape by aligning it with the mold, and the mold was released to obtain a molded body. The mold used in this evaluation was a round-corner container with an opening of 110 mm square and a depth of 35 mm, the bottom was 80 mm square and had a rounded corner shape with R = 10 mm, and the bottom and side wall also had a curved portion with R = 10 mm. A schematic diagram of the shape of the mold is shown in FIG. 1.

(Thermoformability evaluation)
The molded body obtained by the above thermoforming was elongated the most at the bottom corner, resulting in the thinnest thickness. Therefore, the bottom corner and the center of the flat surface of the container bottom were cut out and the thickness of each was measured with a vernier caliper. The thickness ratio was calculated using the following formula 2 and evaluated according to the following criteria.
Equation 2: Thickness ratio = (thickness of bottom corner (mm)) / (thickness of bottom plane (mm))
○: The thickness ratio is 0.7 or more ×: The thickness ratio is less than 0.7

(Measurement of dimensional change rate after thermoforming)
The width of the opening of the molded article was measured immediately after thermoforming and one week after thermoforming, and the dimensional change rate after thermoforming was calculated using Equation 3.
Equation 3: Dimensional change rate after thermoforming = ((width (mm) after 1 week) - (width (mm) immediately after molding)) / (width (mm) immediately after molding) x 100

Example 1
A-1, A-2, and B-1 were charged into a planetary extruder in the compounding ratios shown in Table 1, and melt-kneaded at a set temperature of 140°C. The melt-kneaded resin was then sandwiched between two rolls having a roll diameter of 60 cm, a roll width of 1400 cm, a roll set temperature of 125°C, and a roll rotation speed of 10 rpm to form a sheet. The sheet was stretched in the MD direction while being cooled using a cooling roll having a set temperature of 80°C and whose rotation speed was adjusted so that the stretch ratio was 1.5 times. The width direction end was slit to obtain a thermoforming resin sheet having a width of 1000 mm and a thickness of 0.3 mm.
During sheet molding, the temperature of the resin coming out of the planetary extruder and the temperature of the resin sheet immediately after passing through the cooling roll were measured with a non-contact thermometer. In addition, the resin sheet was subjected to differential scanning calorimetry analysis to measure the melting peak temperature and the end temperature on the high temperature side of the melting peak. The evaluation results are shown in Table 1.
For the evaluation of thermoforming of the resin sheet, a frame having a side of 300 mm was used, and the resin sheet was preheated to a preheating temperature of 140° C., and thermoforming was performed. The evaluation results are shown in Table 1.

Example 2
A thermoforming resin sheet was obtained in the same manner as in Example 1 except for changing the compounding ratio, and a differential scanning calorimetry analysis evaluation and a thermoforming evaluation were carried out. The evaluation results are shown in Table 1.

Example 3
A thermoforming resin sheet was obtained in the same manner as in Example 1 except for changing the compounding ratio, and a differential scanning calorimetry analysis evaluation and a thermoforming evaluation were carried out. The evaluation results are shown in Table 1.

<Comparative Example 1>
A thermoforming resin sheet was obtained in the same manner as in Example 3 except that the stretch ratio was changed to 1.0, and differential scanning calorimetry analysis evaluation and thermoforming evaluation were performed. The evaluation results are shown in Table 1.

[Production of poly(3-hydroxybutyrate)-based resin pellets]
A-1, A-2, and B-1 were dry blended in the compounding ratios shown in Examples 4 to 6 or Comparative Example 2 in Table 2. The obtained resin material was fed into a φ26 mm co-rotating twin-screw extruder with the cylinder temperature and die temperature set to 150° C., extruded, passed through a water tank filled with hot water at 45° C. to solidify the strands, and cut with a pelletizer to obtain resin pellets.

Example 4
The cylinder temperature and die temperature of a φ90 mm single-screw extruder connected to a 1,500 mm wide T-die were each set to 160°C, and the resin pellets were fed and extruded into a sheet using the T-die. After cooling with a first cooling roll with a set temperature of 80°C, the sheet was stretched in the MD direction while being cooled with a second cooling roll with a set temperature of 60°C, the rotation speed of which was adjusted so that the stretch ratio was 1.5 times, and the width direction end was slit to obtain a thermoforming resin sheet having a width of 1,000 mm and a thickness of 0.3 m.
The temperature of the resin coming out of the outlet of the T-die during sheet molding and the temperature of the resin sheet immediately after passing through the second cooling roll were measured with a non-contact thermometer. Differential scanning calorimetry evaluation and thermoforming evaluation of the resin sheet were performed in the same manner as in Example 1. The evaluation results are shown in Table 2.

Example 5
A thermoforming resin sheet was obtained in the same manner as in Example 4 except for changing the compounding ratio, and a differential scanning calorimetry analysis evaluation and a thermoforming evaluation were carried out. The evaluation results are shown in Table 2.

Example 6
A thermoforming resin sheet was obtained in the same manner as in Example 4 except for changing the compounding ratio, and a differential scanning calorimetry analysis evaluation and a thermoforming evaluation were carried out. The evaluation results are shown in Table 2.

<Comparative Example 2>
A thermoforming resin sheet was obtained in the same manner as in Example 6, except that the stretch ratio was changed to 1.0, and differential scanning calorimetry analysis evaluation and thermoforming evaluation were performed. The evaluation results are shown in Table 2.

In the thermoforming resin sheets of Examples 1 to 6, which had a heat shrinkage rate of 2% or more, the thickness of the bottom corners, which are the part that is most stretched by thermoforming, in the molded articles molded from the resin sheets is not extremely thin compared to other parts, and it is clear that the molded articles can be suitably used as containers.

On the other hand, in the thermoforming resin sheets of Comparative Examples 1 and 2, in which the heat shrinkage rate was less than 2%, the thickness of the bottom corners of the molded body molded from the resin sheets was significantly thinner than the other parts.

It can also be seen that the molded bodies of Examples 2, 3, 5, and 6, which contained filler, had a smaller rate of dimensional change after thermoforming than the molded bodies of Examples 1 and 4, which did not contain filler.

11 Frame 12 Resin sheet hanging down from the opening of the frame 13 Drawdown 14 Lowest point of the resin sheet

Claims (14)

A method for producing a molded product , comprising a step of preheating a thermoforming resin sheet containing a poly(3-hydroxybutyrate)-based resin and then molding the same,
The method for producing a molded product, wherein the heat shrinkage rate of the thermoforming resin sheet in the MD direction and/or TD direction measured when the thermoforming resin sheet is heated to 160° C. as the temperature exhibited by the thermoforming resin sheet is 2% or more . The method for producing a molded article according to claim 1, wherein the poly(3-hydroxybutyrate)-based resin contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). The method for producing a molded article according to claim 1 or 2, wherein the thermoforming resin sheet further contains a filler, and the content of the filler is 1 to 100 parts by weight per 100 parts by weight of the poly(3-hydroxybutyrate)-based resin . The method for producing a molded article according to claim 3 , wherein the filler is an inorganic filler. The method for producing a molded article according to claim 4, wherein the inorganic filler comprises at least one selected from the group consisting of silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, and carbon black. The method for producing a molded article according to claim 3 , wherein the filler is an organic filler. The method for producing a molded article according to any one of claims 1 to 6, wherein a difference between a melting peak temperature and an end temperature on the higher side of the melting peak in a differential scanning calorimetry analysis of the poly(3-hydroxybutyrate)-based resin is 10°C or more and 70°C or less. The method for producing a molded product according to any one of claims 1 to 7, wherein the thermoforming resin sheet has a thickness of 0.1 to 1 mm. The method for producing a molded product according to any one of claims 1 to 8, wherein the drawdown of the thermoforming resin sheet measured by the following method is 10 cm or less.
Drawdown: The thermoforming resin sheet, measuring 20 cm in MD x 20 cm in TD, is fixed on a frame measuring 20 cm in length x 20 cm in width x 50 cm in height with a square opening measuring 17.5 cm in length x 17.5 cm in width in the center, and the thermoforming resin sheet is heated to a temperature of 140°C. This is the vertical distance from the fixed surface of the thermoforming resin sheet to the lowest point. The method for producing a molded article according to any one of claims 1 to 9, wherein the thermoforming resin sheet is preheated to a temperature between a melting point peak temperature and an end temperature on the higher side of the melting point peak in a differential scanning calorimetry analysis of the poly(3-hydroxybutyrate)-based resin. The method for producing a molded product according to any one of claims 1 to 10, wherein the thermoforming resin sheet is a sheet stretched uniaxially or biaxially at a stretch ratio of 1.1 times or more. The method for producing a molded article according to claim 11, wherein the stretching ratio is 1.3 times or more. The method for producing a molded body according to any one of claims 1 to 12, wherein the heat shrinkage rate is 5% or more. The method for producing a molded article according to any one of claims 1 to 13, wherein the heat shrinkage rate is 50% or less.

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