JP7661027B2 - Resin molded body, its manufacturing method, and food and beverage products - Google Patents

Description

The present invention relates to a resin molded body, a manufacturing method thereof, and a food or beverage product.

Plastic is used in large quantities as an indispensable material in our daily lives, but the rate at which it is recycled is low, and most of it is dumped back into the environment. Because of its excellent durability, plastic is difficult to decompose, which has led to environmental pollution problems.

To solve this problem, the use of biodegradable plastics has been attracting attention, and biodegradable plastics such as polylactic acid (PLA) and polyvinyl alcohol (PVA) are being used. Technologies for promoting the decomposition of plastics have also been reported. For example, Patent Document 1 discloses a "method for decomposing a resin molded body, characterized in that the resin molded body is decomposed by attaching a decomposition treatment liquid containing a plurality of fatty acid metal salts with different oxidation numbers by any of the methods of coating, sprinkling, spraying, or immersion," and specifically discloses that the decomposition of a polyethylene film is promoted by coating the surface of the film with a decomposition treatment liquid.

International Publication No. 2019/207751

The present invention aims to provide a resin molded body with excellent decomposability and a method for producing the same.

As a result of intensive research, the inventors discovered that a resin molded product containing a specific decomposer and a resin containing polypropylene (PP) has excellent decomposability, leading to the completion of the present invention.

The present invention includes the following embodiments.
[1]
A decomposition agent including a plurality of fatty acid metal salts;
A resin including polypropylene;
Including,
The plurality of metal elements contained in the plurality of fatty acid metal salts are metal elements that can have different oxidation numbers.
Resin molded body.
[2]
The resin molded body according to [1], wherein the decomposition agent is uniformly distributed in the resin molded body.
[3]
The resin molded body according to [1], wherein 50 mass% or more of the decomposition agent contained in the resin molded body is in a mixed state with the resin.
[4]
The resin molded body according to any one of [1] to [3], wherein all of the decomposition agent contained in the resin molded body is in a state of being mixed with the resin.
[5]
The resin molded body according to any one of [1] to [4], wherein the plurality of metal elements are a combination of a transition metal element and a rare earth element.
[6]
The resin molded article according to [5], wherein the transition metal element is manganese and the rare earth element is cerium.
[7]
The resin molded article according to any one of [1] to [6], wherein the fatty acid that forms the fatty acid metal salt is a fatty acid having 12 to 24 carbon atoms.
[8]
The resin molded body according to [7], wherein the fatty acid having 12 to 24 carbon atoms is stearic acid.
[9]
The resin molded body according to any one of [1] to [8], wherein the resin molded body is a resin molded body for forming a food or beverage.
[10]
The resin molded article according to [9], which is a straw, a label, a cap, a container, or a package for forming the food or beverage product.
[11]
[10] The straw according to [10],
A bag enclosing the straw;
Equipped with
Beverages.
[12]
A step of mixing a decomposition agent containing a plurality of fatty acid metal salts and a resin containing polypropylene to obtain a mixture;
forming the mixture into a resin molded product;
Including,
The plurality of metal elements contained in the plurality of fatty acid metal salts are metal elements that can have different oxidation numbers.
A method for producing a resin molded product.
[13]
The method according to [12], wherein 50 mass% or more of the decomposition agent contained in the resin molded body is mixed with the resin.
[14]
The method according to [12] or [13], wherein all of the decomposition agent contained in the resin molded body is mixed with the resin.
[15]
The method according to any one of [12] to [14], wherein the plurality of metal elements is a combination of a transition metal element and a rare earth element.
[16]
The method according to [15], wherein the transition metal element is manganese and the rare earth element is cerium.
[17]
The method according to any one of [12] to [16], wherein the fatty acid that forms the fatty acid metal salt is a fatty acid having 12 to 24 carbon atoms.
[18]
The method according to [17], wherein the fatty acid having 12 to 24 carbon atoms is stearic acid.
[19]
The method according to any one of [12] to [18], wherein the resin molded body is a resin molded body for forming a food or beverage.
[20]
The method according to [19], wherein the resin molded article forming the food or beverage product is a straw, a label, a cap, a container, or a package.

The present invention provides a resin molded body with excellent decomposability and a method for producing the same.

Figure 1 shows the results of a 360-day biodegradation test on a double straw (degradation agent: 1.0% by mass) that had undergone an oxidative decomposition test. Cellulose was used as a control.

The following describes in detail the embodiments of the present invention, but the present invention is not limited to these, and various modifications are possible without departing from the spirit of the invention.

<Resin Molded Body>
One embodiment of the present invention relates to a resin molded body comprising a decomposing agent containing a plurality of fatty acid metal salts and a resin containing polypropylene, wherein the plurality of metal elements contained in the plurality of fatty acid metal salts are metal elements that can have different oxidation numbers from each other.

The resin molded body according to this embodiment has excellent degradability, and therefore has the advantage that it is less likely to cause environmental pollution compared to conventional plastic products, even if it is dumped in the natural environment. Specifically, it is believed that the decomposition of the resin molded body proceeds in two steps: oxidative decomposition, as described below, followed by biodegradation (microbial decomposition).

Step 1 (oxidative decomposition): Using sunlight (ultraviolet rays), heat, oxygen, water, etc. as energy sources, the metal elements contained in the decomposer generate fatty acid radical components through their catalytic effect, which oxidatively decompose the carbon-carbon bonds of the resin that makes up the resin molded body. This reduces the physical properties (strength, elongation) and molecular weight of the resin molded body.

Step 2 (biodegradation): The oxidized low molecular weight products (e.g., carboxylic acid alcohols) formed in step 1 are digested and absorbed by microorganisms in the soil or compost environment. Ultimately, they are stored in the microorganisms' bodies as biomass and converted into carbon dioxide and water through metabolic activities such as respiration.

(Decomposer)
The decomposing agent used in the present embodiment contains a plurality of fatty acid metal salts, and the plurality of metal elements contained in the plurality of fatty acid metal salts are metal elements that can have different oxidation numbers. The number of fatty acid metal salts is not particularly limited as long as it is two or more types, but may be, for example, two to four types, two or three types, two types, etc.

The mechanism by which the decomposition agent decomposes the resin is assumed to be as follows, but the present invention is not limited to this mechanism in any way.
Due to the influence of light, heat, etc., an alkyl radical (R.) is generated in the resin (RH) (Formula 1), which reacts with oxygen to generate a peroxy radical (ROO.) (Formula 2). The peroxy radical (ROO.) reacts with the resin (RH) to promote decomposition of the resin, and at this time the peroxy radical (ROO.) becomes a hydroperoxide (ROOH) and is stabilized (Formula 3). Here, multiple fatty acid metal salts contained in the decomposing agent cleave the hydroperoxide (ROOH) to generate new radicals (RO. and ROO.) (Formulas 4 and 5). These radicals further decompose the resin (RH) (Formulas 6 and 7).
Formula 1: RH→R・+H・
Formula 2: R・+O ₂ →ROO・
Equation 3: ROO + RH → ROOH + R
Formula 4: M ₁ (n) ⁺ +ROOH→M ₁ (n+1) ⁺ +RO・+HO ^-
Formula 5: M ₂ (n+1) ⁺ +ROOH→M ₂ (n) ⁺ +ROO・+H ⁺
Equation 6: RO + RH → ROH + R
Equation 7: ROO + RH → ROOH + R
(In the formula, _M1 ⁺ and _M2 ⁺ are each a metal cation, and n and n+1 are each an oxidation number.)

The number of metal elements forming the fatty acid metal salt is not particularly limited as long as it is two or more types, but may be, for example, two to four types, two or three types, two types, etc. Examples of metal elements include transition metal elements and rare earth elements.
Examples of transition metal elements include titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, technetium, ruthenium, palladium, silver, and cadmium.
Examples of rare earth elements include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

The metal elements forming the fatty acid metal salt are selected so that they can have different oxidation numbers. Although not particularly limited, a combination of a transition metal element and a rare earth element is preferable, and a combination of manganese (oxidation numbers: divalent, trivalent) and cerium (oxidation numbers: trivalent, tetravalent) is more preferable.

The fatty acid metal salt may be formed from one type of fatty acid or a combination of two or more types. Examples of fatty acids include saturated or unsaturated fatty acids having 12 or more carbon atoms. Examples include lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, henicosylic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, and nervonic acid.

The fatty acid that forms the fatty acid metal salt is preferably a fatty acid having 12 to 24 carbon atoms, more preferably a fatty acid having 16 to 20 carbon atoms, and even more preferably stearic acid or oleic acid.

The amount of decomposition agent may be appropriately selected so that the resin molding decomposes in the desired period of time. Although not particularly limited, the amount of decomposition agent may be 0.02 to 6.0 mass%, 0.1 to 4.0 mass%, 0.2 to 3.0 mass%, 0.3 to 2.0 mass%, 0.4 to 1.4 mass%, etc., based on the mass of the resin molding.

(resin)
The resin used in this embodiment includes polypropylene. Examples of polypropylene include propylene homopolymer, propylene random polymer, and propylene block polymer.

The resin may contain only polypropylene, or may contain other resins depending on the desired resin molded product. Examples of other resins include thermoplastic resins other than polypropylene, such as polyethylene, polybutadiene, polyacetal, polyamide, polyethylene terephthalate, polycarbonate, polystyrene, polyphenylene sulfide, polybutylene terephthalate, polyvinyl chloride, ABS resin, and AS resin.

The amount of polypropylene contained in the resin is not particularly limited, but may be, for example, 10 to 100 mass%, 20 to 100 mass%, 30 to 100 mass%, 40 to 100 mass%, 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass%, or 90 to 100 mass% based on the mass of the resin.

(Optional ingredients)
The resin molded product according to the present embodiment may contain optional components in addition to the above-mentioned decomposition agent and resin. Optional components include, for example, colorants, and specific examples of colorants include colorants listed in the Food Sanitation Act, such as edible red, edible yellow, and titanium oxide.

(Resin Molded Body)
The resin molded body according to the present embodiment includes a decomposing agent and a resin. The decomposing agent may be uniformly distributed in the resin molded body. In this specification, "uniformly distributed" means that the concentration of the decomposing agent present on the surface of the resin molded body is substantially the same as the concentration of the decomposing agent present inside the resin molded body. Note that when the surface of the resin molded body is treated with a decomposing agent after formation, the concentration of the decomposing agent is high on the surface and low inside, so that the decomposing agent is not uniformly distributed.

50% or more by mass of the decomposition agent contained in the resin molded body may be in a state mixed with the resin. The ratio of the decomposition agent in a state mixed with the resin may be 50-100% by mass, 60-100% by mass, 70-100% by mass, 80-100% by mass, 90-100% by mass, or 100% by mass. The decomposition agent that is not in a state mixed with the resin may be present, for example, in a state attached to the surface portion of the resin molded body.

Regarding the degradability of the resin molded body, in the decomposition test described in the examples below, the degree of biodegradation in a specified period is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. The rate of decomposition can be adjusted as appropriate by changing the amount of the decomposition agent.

The resin molded body is not particularly limited, but is preferably a resin molded body that forms a food or beverage. In this specification, "food or beverage" includes not only things that are ingested into the body, but also accessories such as containers. Therefore, the resin molded body that forms a food or beverage corresponds to accessories of the food or beverage. Examples of the resin molded body that forms a food or beverage include straws, straw bags, labels, caps, containers, and packaging.

The resin molded product forming the food or beverage product is not particularly limited, but is preferably one that comes into contact with the human mouth, and is more preferably a straw. If the resin molded product comes into contact with the human mouth, it is preferable that the decomposition agent be mixed with the resin to avoid a situation in which the decomposition agent is unevenly distributed on the surface of the resin molded product.

A specific example of a food or beverage product is a beverage product that includes a straw and a bag that encloses the straw. By enclosing the straw in a bag that has certain properties, it is possible to prevent the straw from starting to decompose before use.

<Method of manufacturing resin molded body>
One embodiment of the present invention relates to a method for producing a resin molded body, comprising: a step of mixing the decomposition agent and the resin to obtain a mixture (mixing step); and a step of molding the mixture into a resin molded body (molding step).

(Mixing process)
In the mixing step, the decomposing agent and the resin are mixed to obtain a mixture. Details of the decomposing agent and the resin are as described in the <Resin Molded Product> section above. In the mixing step, 50% by mass or more of the decomposing agent contained in the resin molded product may be mixed with the resin. The amount of the decomposing agent mixed with the resin may be 50 to 100% by mass, 60 to 100% by mass, 70 to 100% by mass, 80 to 100% by mass, 90 to 100% by mass, or 100% by mass based on the total mass of the decomposing agents used.

In the mixing process, a portion of the resin may be premixed with the decomposer to form pellets, which are then mixed with the remaining resin. By mixing in this manner, it becomes easier to mix the decomposer uniformly into the resin.

When the resin molded body is to come into contact with the human mouth, it is preferable to mix all of the decomposition agent with the resin. When all of the decomposition agent is sufficiently mixed with the resin, the decomposition agent will be uniformly distributed in the resin molded body. On the other hand, when there is a decomposition agent that does not mix with the resin, the decomposition agent may be attached, for example, to the surface portion of the resin molded body. In this case, following the molding process, a process of attaching the decomposition agent to the surface portion of the resin molded body (attachment process) may be added.

(Molding process)
In the molding step, the mixture obtained in the mixing step is molded into a resin molded product. The molding method is not particularly limited, and a known method (e.g., extrusion molding, injection molding, compression molding, or vacuum molding) may be used depending on the shape of the desired resin molded product. Details of the resin molded product are as described in the <Resin molded product> section above.

(Attachment process)
The decomposing agent that is not mixed with the resin may be attached to the surface of the resin molded body. Examples of the method for attachment include a method of applying, scattering or spraying a solution or dispersion of the decomposing agent to the surface of the resin molded body, or a method of immersing the resin molded body in a solution or dispersion of the decomposing agent.

The present invention will be described in more detail below using examples, but the technical scope of the present invention is not limited to these examples.

<Production of degradable straws>
Polypropylene resin, low-density polyethylene resin, and decomposers (manganese stearate and cerium stearate) were mixed in a blender, melted at 200-240°C, and extruded to create an outer straw (decomposer: 0.3% by mass). An inner straw (decomposer: 0.3% by mass) was also created in the same manner. The inner straw was inserted into the outer straw to create a double straw (decomposer: 0.3% by mass).

Double straws containing 0.6% and 1.0% by mass of decomposition agent were created using the same method, except that the amount of decomposition agent was changed.

<Decomposition test>
(Oxidative decomposition process)
The prepared double straw (decomposition agent: 1.0 mass %) was subjected to oxidative decomposition for 15 days using the following device and conditions.
Equipment: Gear oven (Espec Corporation; model GPH-102)
In-flight test temperature: 80℃
Aircraft wind speed setting: Level 2 (light breeze)

(Biodegradation process)
The double straw that had undergone the oxidative decomposition process was subjected to a biodegradation process in accordance with Japanese Industrial Standards (JIS) K6955: 2017. Microcrystalline cellulose was also used as a comparative control.

The details of the biodegradation process are as follows:
1. Sample preparation The samples that had been subjected to the oxidative decomposition process were frozen and crushed, and passed through sieves with openings of 250 μm and 125 μm to classify the particles into particle sizes of 125 to 250 μm.

2. Total organic carbon and total theoretical carbon dioxide generation The total organic carbon (TOC) of the samples was measured using a CHN analyzer (Microcorder JM10, manufactured by J Science Labs), and the total theoretical carbon dioxide generation (ThCO ₂ ) was calculated from the TOC.

3. Soil Soil collected from the surface of a field in Hitachi-Omiya City, Ibaraki Prefecture in July 2019 was used. 25 mL of purified water was added to 5 g of soil, and the pH was measured by shaking and mixing to be 6.3.

4. Test conditions Measurement method: Measurement of carbon dioxide generation amount (potentiometric titration method)
Potentiometric titration conditions Measuring device: Automatic potentiometric titrator (Kyoto Electronics Industry AT-610, MCU-610, EBU-610-20B, CHA-600-12)
Electrode: Composite glass electrode (Kyoto Electronics Manufacturing Co., Ltd. C-171)
Measurement reagent: 0.5 mol/L HCl solution Carbon dioxide absorption solution: 0.5 mol/L KOH solution (90 mL in duplicate)
Test container volume: 500 mL
Amount of sample: 1 g
Amount of soil: 400g
Culture temperature: 25±2°C
Number of measurements: 29

5. Results The degree of biodegradation calculated from the amount of carbon dioxide generated and _ThCO2 is shown in Table 1 and Figure 1. This result shows that even for polypropylene resin, which is difficult to biodegrade, the biodegradation can be promoted by using a decomposition agent.

Claims (15)

A decomposition agent including a plurality of fatty acid metal salts;
A resin including polypropylene;
Including,
The plurality of metal elements contained in the plurality of fatty acid metal salts are metal elements that can have different oxidation numbers.
A resin molded body ,
the decomposition agent is uniformly distributed in the resin molded body,
the plurality of metal elements are a combination of a transition metal element and a rare earth element,
The resin molded article, wherein the transition metal element is manganese and the rare earth element is cerium. The resin molded body according to claim 1, wherein 50% by mass or more of the decomposition agent contained in the resin molded body is mixed with the resin. The resin molded article according to claim 1 , wherein all of the decomposition agent contained in the resin molded article is in a state of being mixed with the resin. 4. The resin molded article according to claim 1 , wherein the fatty acid forming the fatty acid metal salt is a fatty acid having 12 to 24 carbon atoms. The resin molded article according to claim 4 , wherein the fatty acid having 12 to 24 carbon atoms is stearic acid. The resin molded article according to any one of claims 1 to 5 , which is a resin molded article for forming a food or beverage product. The resin molded article according to claim 6 , which is a straw, a label, a cap, a container, or a package for a food or beverage product. A straw according to claim 7 ;
A bag enclosing the straw;
Equipped with
Beverages. A step of mixing a decomposition agent containing a plurality of fatty acid metal salts and a resin containing polypropylene to obtain a mixture;
forming the mixture into a resin molded product;
Including,
the plurality of metal elements contained in the plurality of fatty acid metal salts are metal elements that can have different oxidation numbers,
the plurality of metal elements are a combination of a transition metal element and a rare earth element,
The transition metal element is manganese and the rare earth element is cerium;
A method for producing a resin molded product. The method according to claim 9 , wherein 50% by mass or more of the decomposition agent contained in the resin molded body is mixed with the resin. The method according to claim 9 or 10 , wherein all of the decomposition agent contained in the resin molded body is mixed with the resin. The method according to any one of claims 9 to 11 , wherein the fatty acid that forms the fatty acid metal salt is a fatty acid having 12 to 24 carbon atoms. The method according to claim 12 , wherein the fatty acid having 12 to 24 carbon atoms is stearic acid. The method according to any one of claims 9 to 13 , wherein the resin molded article is a resin molded article for forming a food or beverage. The method according to claim 14 , wherein the resin molded article forming the food or beverage product is a straw, a label, a cap, a container, or a package.