JP7587376B2 - Biodegradable paper containers - Google Patents

Description

The present invention relates to a novel biodegradable paper container. In particular, it relates to a disposable container that is heated and cooked in a microwave oven or the like.

In recent years, in order to reduce the burden on the environment, the distribution of various disposable containers made primarily from soil-degradable biodegradable plastics has been promoted. The advantage of using known biodegradable plastics is that they are decomposed into water and carbon dioxide by the natural self-purifying action, disappear completely, and do not remain in the ground. In this respect, it is not only extremely preferable from the perspective of waste disposal, but even if they are incinerated, they have a low combustion calorie of about half or less compared to synthetic resins such as polyethylene, which reduces disposal costs.

Well-known representative examples of disposable paper containers include paper cups for beverages, whose base paper is a laminate of "plastic layer/paper" where a plastic material is laminated on at least one side of a paper substrate, and paper cups for instant noodles that are heated and cooked in hot water. Most of the plastic materials used in the plastic layers of these base papers are non-biodegradable plastics. The reasons why these non-biodegradable plastics cannot be replaced by biodegradable plastics include not only cost and productivity, but also insufficient heat resistance. For this reason, containers made of biodegradable materials with improved heat resistance have been proposed.

For example, Patent Document 1 discloses a paper container having a bottom and a body made of a paper base material with a resin sheet on the inner surface, characterized in that the resin sheet is made of a biodegradable plastic that is uniaxially or biaxially stretched and has thermal adhesive properties.

Patent document 2 discloses a biodegradable container made by adhering a biodegradable film made primarily from plants to the inner surface of a molded food container made from non-wood fibers (reed, kenaf, sugar cane, corn).

JP 2003-26143 A JP 2008-18703 A

However, according to research by the inventors of the present application, when a paper container such as that described in Patent Document 1 is filled with commercially available white sauce used in gratins and the like and heated in a microwave oven, the biodegradable resin layer peels off from the paper base material due to poor heat resistance, and large air bubbles are generated in the biodegradable resin layer, making it difficult to withstand cooking with heat.

In addition, problems such as delamination between the biodegradable resin layer and the paper base material are unlikely to occur if the structure is made by bonding together laminates with separate bottom and side surfaces, such as a paper cup. However, when a single laminate is processed into an integrated container shape by press molding or other processing, the laminate is pulled and squeezed during molding, exerting strong forces on it, which may cause the biodegradable resin to peel off from the paper base material, or cause pinholes or tears, due to the adhesiveness between the biodegradable resin layer and the paper base material, etc.

Therefore, the main object of the present invention is to provide a biodegradable paper container that has excellent adhesion between the paper base material and the biodegradable resin layer, excellent moldability, and also has high heat resistance.

As a result of extensive research into the problems of the prior art, the inventors discovered that a container with a specific layer structure could achieve the above objective, leading to the completion of the present invention.

That is, the present invention relates to the following biodegradable paper container.
1. A container comprising a laminate including a paper base material and a polylactic acid resin-containing layer on one or both sides of the paper base material,
(1) The basis weight of the paper base material is 150 to 500 g/ ^m2 ;
(2) The thickness of the polylactic acid resin-containing layer is 10 to 55 μm.
A biodegradable paper container characterized by the above.
2. The biodegradable paper container according to item 1, wherein the polylactic acid resin contained in the polylactic acid resin-containing layer has a biodegradability of 30 to 70%.
3. The biodegradable paper container according to item 1 or 2, wherein the content of the polylactic acid resin in the polylactic acid resin-containing layer is 80 to 100% by weight.
4. The biodegradable paper container according to any one of items 1 to 3, wherein the polylactic acid resin-containing layer is laminated on at least the inner surface of the container.
5. The biodegradable paper container according to any one of items 1 to 4, characterized in that the container is composed of a) a bottom portion, b) a side wall portion connected to the periphery of the bottom portion and rising upward, c) a flange portion connected to the upper end of the side wall portion and extending in a substantially horizontal direction, and d) a rolled rim portion connected to the outer periphery of the flange portion.
6. A method for producing a biodegradable paper container, comprising:
A method for producing a biodegradable paper container, comprising: (1) a step of laminating a polylactic acid resin-containing composition onto at least one surface of a paper substrate having a basis weight of 150 to 500 g/ ^m2 using a T-die extruder to obtain a laminate having a thickness of 10 to 55 μm; and (2) a step of forming the laminate into a container shape having a recess by press molding.

The present invention provides a biodegradable paper container that has excellent adhesion and moldability between the paper base material and the biodegradable resin layer, as well as high heat resistance.

In particular, the combination of a paper base material with a specific basis weight and a specific polylactic acid resin-containing layer makes it difficult for the container itself (especially the polylactic acid resin-containing layer) to change or deteriorate even when heated in a microwave oven or the like, so it can be used with any type of content (heated or non-heated).

In addition, the adhesiveness between the paper base material and the polylactic acid resin-containing layer is excellent, so problems such as delamination are unlikely to occur when heated. Furthermore, the occurrence of pinholes and other problems that can occur during molding can be prevented, ensuring high reliability as an integrally molded container.

According to the manufacturing method of the present invention, a molten polylactic acid resin-containing composition is melt-extruded onto a specific paper substrate to produce a laminate, and then the laminate is molded, so that a container having good adhesion between the paper substrate and the biodegradable resin layer, as described above, can be efficiently manufactured.

The container of the present invention, which has these characteristics, can be used as a container for storing various products, and is particularly suitable for use as a container in which both the container and the contents are heated (particularly in a microwave oven). More specifically, it can be used as tableware for cooked products (boxed lunches, side dishes, gratin, curry and rice, pasta, rice bowls, ramen, udon, soup, stew, coffee, juice, and other foods and beverages) in convenience stores, supermarkets, and the like.

1 shows the layer configuration of a laminate used to manufacture the container of the present invention. 1 shows a cross-sectional configuration of a container according to an embodiment of the present invention. 1 shows a cross-sectional configuration of a container according to an embodiment of the present invention. 1 shows an enlarged view of a flange portion of a container of the present invention. 1 shows an image of a paper container produced in an embodiment.

The biodegradable paper container of the present invention (the container of the present invention) is a container comprising a paper base material and a laminate including a polylactic acid resin-containing layer on one or both sides of the paper base material,
(1) The basis weight of the paper base material is 150 to 500 g/ ^m2 ;
(2) The thickness of the polylactic acid resin-containing layer is 10 to 50 μm.
It is characterized by:

The laminate constituting the container of the present invention is a laminate containing a paper base material and a polylactic acid resin-containing layer on one or both sides of the paper base material. For example, FIG. 1 shows an example of a laminate. In the laminate 10 of FIG. 1A, a polylactic acid resin-containing layer 12 is laminated on one side of a paper base material 11. In the laminate 10' of FIG. 1B, polylactic acid resin-containing layers 12, 12' are laminated on both sides of a paper base material 11. In the laminate 10 or 10', other layers (e.g., adhesive layers, sealant layers, printed layers, etc.) may be appropriately formed between the paper base material and the polylactic acid resin-containing layer within a range that does not impede the effects of the present invention. Furthermore, other layers may be arranged as necessary on the other side of the surface of the paper base material that is not in contact with the polylactic acid resin-containing layer within a range that does not impede the effects of the present invention. Similarly, other layers may be arranged as necessary on the other side of the surface of the paper base material that is not in contact with the polylactic acid resin-containing layer within a range that does not impede the effects of the present invention.

The total thickness of the laminate is not particularly limited and can be set appropriately depending on the form of use, application, type of contents, etc., and can be within the range of, for example, about 160 to 700 μm, but is not limited to this.

In addition, in the container of the present invention, when the laminate is molded, it is preferable to mold the polylactic acid resin-containing layer so that it is disposed on the inner surface of the container. A cross-sectional view of an example of the container of the present invention is shown in FIG. 2. In FIG. 2, the laminate 10 is molded into a concave shape (cup shape), and the polylactic acid resin-containing layer 12 is disposed on the inner surface (inner layer) of the container, and the paper base material 11 is disposed on the outside. In other words, the contents filled in the container are disposed so that they come into direct contact with the polylactic acid resin-containing layer 12. In this case, even if the contents come into contact with the polylactic acid resin-containing layer, the polylactic acid resin-containing layer prevents the contents from touching the paper base material, so that the shape of the container can be effectively maintained at least during use.

Another embodiment of the container of the present invention is shown in Figure 3. The container 20 in Figure 3 is composed of a) a bottom portion B, b) a side wall portion S that connects to the periphery of the bottom portion and rises upward, and c) a flange portion F that connects to the upper end of the side wall portion and extends in a substantially horizontal direction. In the present invention, it is preferable that the container has a flange portion that projects outward in a horizontal direction around the entire periphery of the peripheral wall that constitutes the recess (cup). This structure not only increases the strength of the container, but also makes it easy to grasp the flange portion with the fingers even when the contents become hot after cooking, making it possible to carry the paper container.

The flange portion F of the container in FIG. 3 can be further processed to form a rolled edge portion. FIG. 4 shows an enlarged view of the flange portion F. In FIG. 4A, the flange portion F is formed to extend in a substantially horizontal direction. In contrast, as shown in FIG. 4B, the edge portion of the flange portion is processed to form the rolled edge portion R. In other words, the present invention also includes a container that is composed of a) a bottom portion, b) a side wall portion that connects to the periphery of the bottom portion and rises upward, c) a flange portion that connects to the upper end of the side wall portion and extends in a substantially horizontal direction, and d) a rolled edge portion that is connected to the outer periphery of the flange portion. In this way, by providing the rolled edge portion, the strength, etc. of the container can be further increased.

The container of the present invention preferably has an integral structure of a) to c) or a) to d). For example, it is preferable that a) to c) or a) to d) are not composed of separate members, but have a seamless structure. Such a structure can be produced by integrally molding the laminate into the shape of a container by a press molding method or the like.

The container of the present invention is not particularly limited as long as it has a shape that can hold the contents, and is preferably a container that is molded in a concave shape so that it can hold food (cooked food). Therefore, for example, it can be used as a tray, plate, bowl, paper cup, etc. The components of the container of the present invention (paper base material, polylactic acid resin-containing layer, etc.) are described below.

(1) Paper Substrate The paper substrate serves as a substrate for supporting the polylactic acid resin-containing layer and also plays a role in ensuring the rigidity of the container.

The paper base material has a basis weight of 150 to 500 g/ ^m2 . If the basis weight is less than 150 g/ ^m2 , the rigidity is poor when filled with food ingredients, resulting in insufficient strength as a food container, whereas if the basis weight is more than 500 g/ ^m2 , the moldability is significantly reduced, resulting in high costs and over-specification as a food container.

The paper base material is not particularly limited as long as it has the above-mentioned basis weight, and various paper base materials used in publicly known or commercially available paper containers can be used. For example, pure white roll paper, craft paper, parchment paper, ivory paper, manila paper, card paper, cup paper, etc. can be used depending on the desired application. Recycled paper can also be used as the paper.

There are no limitations on the thickness of the paper base material as long as it satisfies the above-mentioned basis weight. For example, the thickness can be about 150 to 600 μm, but is not limited to this.

(2) Polylactic Acid Resin-Containing Layer The polylactic acid resin-containing layer mainly functions to prevent or inhibit the penetration of the contents into the paper base material, and thus contributes to the shape retention of the container.

The content of polylactic acid resin in the polylactic acid resin-containing layer is not particularly limited, but is usually 80 to 100% by mass, and preferably 90 to 98% by mass. Therefore, it can be, for example, 98 to 100% by mass.

In the present invention, one of the reasons for using polylactic acid resin as the main component in the polylactic acid resin-containing layer is its unique biodegradation mechanism. It is believed that the biodegradation mechanism is that after decomposition progresses to a molecular weight of about 10,000 by hydrolysis (more specifically, environmental factors of temperature 60°C or higher, humidity 80% or higher, and pH 8 or higher), the decomposition is accelerated by microorganisms, and finally decomposed into carbon dioxide and water. This shows that polylactic acid resin is as stable as non-biodegradable plastics unless it is exposed to high temperature and high humidity conditions for a certain period of time. Therefore, for example, when used as a food container, it is possible to maintain the service period or product life as long as possible in the general distribution process until the end consumer eats it, and at the disposal stage, it is possible to obtain disposal characteristics with low environmental impact as quickly as possible. In this respect, the container of the present invention can be suitably used, for example, as a one-way (disposable) food container.

The polylactic acid resin may be either a homopolymer or copolymer formed by polymerization of lactic acid (at least one of L-lactic acid (L-form) and D-lactic acid (D-form)) via ester bonds, or a copolymer formed by polymerization of lactic acid and another copolymer component (for example, an acid component such as glycolic acid). In particular, in the present invention, a homopolymer or copolymer formed by polymerization of lactic acid (at least one of L-lactic acid and D-lactic acid) is preferred. In the present invention, one or more of these polylactic acid resins may be used.

When the polylactic acid resin is substantially composed of lactic acid, the monomers may be a) substantially L-type, b) substantially D-type, or c) both L-type and D-type. In the present invention, a copolymer containing both L-type and D-type is preferred, and a copolymer containing 1 to 10% by mass of D-type is more preferred. In general, L-type polylactic acid resin has superior mechanical properties, but if it is composed of only L-type, the structure may become brittle and the processability may become poor. Specifically, when polylactic acid is randomly copolymerized with 1 to 10% by mass of D-type, it becomes soft, the crystallinity decreases, and the melting point decreases. This reduces brittleness and balances the physical properties such as processability, mechanical properties, and heat resistance as a container. Therefore, in the present invention, a copolymer composition in which the D-type is 1 to 10% by mass and the remainder is L-type is preferred.

In addition, in the present invention, a polylactic acid resin having a melt flow rate (MFR: 210°C, 2.16 kg load) of 1 to 30 g/10 min, particularly 3 to 20 g/10 min, is preferred. This further improves processing stability when producing a laminate. If the MFR is less than 1/10 min, the extruder may stop due to an increase in the motor load during extrusion. If the MFR exceeds 30 g/10 min, processability may decrease due to increased necking and surging during high-temperature extrusion.

The polylactic acid resin itself having these characteristics can be a publicly known or commercially available product. For example, commercially available products include "2003D", "2500HP", and "4060D" manufactured by Nature Works.

Other components may be added to the polylactic acid resin-containing layer within the range that does not impair the effects of the present invention. Examples include additives that improve various physical properties such as heat resistance, such as adipic acid ester mixtures, rosin-based mixtures, and polyglycerin fatty acid esters. In the present invention, it is preferable that the polylactic acid resin-containing layer is formed from a polylactic acid resin to which no additives have been actively added, that is, a polylactic acid resin with high purity. Therefore, for example, a polylactic acid resin-containing layer with a polylactic acid resin content of 99 to 100% by mass can be preferably used.

In the present invention, the biodegradability of the polylactic acid resin contained in the polylactic acid resin-containing layer is not particularly limited, but is usually preferably about 30 to 70%, and more preferably 35 to 55%. If the biodegradability is less than 30%, the biodegradability is poor and there is a risk that the resin will not decompose quickly even if it is disposed of in the natural environment after use as a container. On the other hand, if the biodegradability is more than 70%, the resin is easily decomposed and there is a risk that the decomposition will progress even during use as a container. The biodegradability of such polylactic acid resin can be appropriately adjusted by the ratio of the linear structure and branched structure of the polylactic acid resin in the polylactic acid resin-containing layer and the presence or absence of functional groups. Therefore, by controlling the biodegradability of the polylactic acid resin to 30% or more and 70% or less, it is possible to more reliably achieve both stability and disposal characteristics with less environmental impact (i.e., rapid degradability).

The biodegradation mechanism referred to here is generally quantified by the biodegradability test stipulated in the Japanese Industrial Standards JIS K6953-1 and -2. The value obtained here is also called the "degree of biodegradation" and indicates the proportion of organic matter decomposed by the action of microorganisms in a certain period of time as a percentage, and is an index of the ease of decomposition in the environment. Here, the degree of biodegradation in this invention complies with the above-mentioned JIS, but the test period is set to 12 days in order to observe the initial tendency of decomposition, and the degree of biodegradation (decomposability) for that number of test days is shown.

The thickness of the polylactic acid resin-containing layer is not particularly limited, but is usually 10 to 55 μm, particularly 10 to 50 μm, and preferably 15 to 45 μm. If the thickness is less than 10 μm, the heat resistance will be insufficient from the viewpoint of heat capacity, and the anchoring effect to the paper will not be obtained, which will induce delamination during cooking in a microwave oven. If the thickness exceeds 55 μm, the processability of the extrusion laminate will be significantly reduced, resulting in high costs, and the container forming processability in press forming processing, for example, as described below, will also be significantly reduced.

The polylactic acid resin-containing layer may be one layer (single layer) of polylactic acid resin-containing layer, or may be two or more layers of polylactic acid resin-containing layers laminated together. For example, when the polylactic acid resin-containing layer is a layer structure of two or more layers by co-extrusion, different raw materials can be used for each layer. For example, a polylactic acid resin-containing layer having excellent adhesion to the paper substrate can be arranged on the layer in contact with the paper substrate, and a polylactic acid resin-containing layer having functions such as surface heat resistance and low-temperature sealability can be arranged on the layer opposite to the side in contact with the paper substrate, thereby more reliably achieving both adhesion to the paper substrate and heat resistance as a container. In addition, by forming a structure of two or more layers by co-extrusion, it is possible to control the balance of melt viscosity between layers, which suppresses an increase in neck-in or the occurrence of surging, and is expected to stabilize the molten film and increase its speed.

The polylactic acid resin-containing layer is preferably an unstretched layer. If a stretched layer (film) is used, the desired heat resistance may not be obtained. For example, a laminate obtained by laminating a pre-stretched polylactic acid resin-containing film and a paper substrate by dry lamination may not have the desired heat resistance, etc.

(3) Other layers In addition to the above-mentioned paper substrate and polylactic acid resin-containing layer, the container of the present invention may appropriately contain any layer or component within a range that does not completely inhibit cooking with heat or biodegradation. For example, a printed layer for imparting information, patterns, illustrations, and other designs related to the contents or the paper container may be provided between the paper substrate and the polylactic acid resin-containing layer or on the surface of the paper substrate. A sealant layer may also be provided on the flange.

In addition, as long as the polylactic acid resin-containing layer is laminated on at least one side of the paper base material, the polylactic acid resin-containing layer may be laminated on one side or both sides. When the polylactic acid resin-containing layer is laminated on only one side of the paper base material, the side on which the polylactic acid resin-containing layer is laminated may be the side that holds the contents of the paper container or the back side thereof, but it is preferable that the polylactic acid resin-containing layer is laminated on the side that holds the contents of the paper container. This makes it possible to prevent part of the contents from seeping into the paper base material, even if the contents contain moisture or oil. It also makes it possible to reduce the contents from adhering to the paper container and becoming difficult to remove.

The container of the present invention is made of a biodegradable material, so it can be particularly well suited for use as a disposable container (tableware).

The target contents are not particularly limited, and can be applied to various products in addition to food. Examples of food include food and beverages (prepared or processed foods such as bento, side dishes, doria, gratin, curry, pasta, udon, soba, donburi, ramen, soup, stew, ice cream, etc., and beverages such as water, coffee, tea, beer, wine, and juice). Therefore, the containers can be widely used as containers for food and beverages such as fast food products and take-out products, as well as food and beverage containers used for eating and drinking in commercial facilities, hospitals, schools, outdoor activities, etc.

The container of the present invention has excellent heat resistance and can be suitably used as a container for storing food to be heated. In particular, it can be advantageously used as a container for heating in a microwave oven. Therefore, the container of the present invention can withstand heating for about 1 to 5 minutes at about 500 to 1000 W in a commercially available microwave oven.

2. Method for Producing Biodegradable Paper Containers The method for producing the container of the present invention is not particularly limited, but for example, the following method can be adopted. That is, a method for producing a biodegradable paper container, comprising the steps of:
(1) A step of laminating a polylactic acid resin-containing composition onto at least one surface of a paper substrate having a basis weight of 150 to 500 g/ ^m2 using a T-die extruder to obtain a laminate having a thickness of 10 to 55 μm (lamination step); and (2) a step of forming the laminate into a container shape having a recess by press molding (molding step).
A method for producing a biodegradable paper container comprising the steps of:

In the lamination process, a polylactic acid resin-containing composition is laminated to a thickness of 10 to 55 μm (preferably 10 to 50 μm, more preferably 15 to 45 μm) on at least one side of ^a paper base material having a basis weight of 150 to 500 g/m2 using a T-die extruder to produce a laminate.

The T-die extruder may be any device capable of simultaneously extruding the molten polylactic acid resin-containing composition and the paper substrate into a sheet, and any known or commercially available device may be used. The laminate extruded by the T-die extruder is obtained as a laminate including the paper substrate and a polylactic acid resin-containing layer on one or both sides of the paper substrate.

When forming polylactic acid resin-containing layers on both sides of a paper substrate, either a) a method of extruding a molten polylactic acid resin-containing composition so that it contacts both sides of the paper substrate, or b) a method of forming a polylactic acid resin-containing layer on one side of the paper substrate in advance, and then extruding the molten polylactic acid resin-containing composition so that it contacts the other side of the paper substrate, can be used.

The polylactic acid resin-containing composition contains polylactic acid resin and additives as necessary. Examples of these polylactic acid resins and additives include those described above in "1. Biodegradable paper containers."

In the molding step, the laminate is molded into a container shape having a recess by press molding.

The press molding method is not particularly limited, and methods and conditions used in molding publicly known or commercially available paper containers can be used. It can also be performed using a publicly known or commercially available press molding machine. For example, the laminate can be subjected to a press molding machine under heating at a temperature of 60 to 120°C and molded into the shape of a container.

The shape of the container is not limited as long as it is concave enough to hold the contents, and can be set appropriately depending on the type of contents, application, and purpose of use. For example, a cup shape, a curry dish shape, etc. can be used. The size of the container is also not particularly limited, and can be set appropriately depending on the application, etc.

In addition, the molding process can also include a process of providing a flange portion and a rolled edge portion to the container of the present invention. These processes can also be carried out using a known or commercially available molding machine.

The following examples and comparative examples are presented to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples.

Example 1
A commercially available polylactic acid resin (Nature Works'"2003D", D-form content: 2-3.5% by mass, MFR: ⁶ (g/10 min-210°C, 2.16 kg), biodegradability: 36%) was melt-extruded to a thickness of 30 μm onto one side of a piece of paper measuring 243 cm long x 184 cm wide and having a basis weight of 260 g/m2, using a commercially available T-die extruder to produce a base paper (laminate) in which a polylactic acid resin-containing layer was laminated on one side of the paper base material.

Example 2
A base paper was prepared in the same manner as in Example 1, except that the polylactic acid resin-containing layer was formed to a thickness of 10 μm.

Example 3
A base paper was prepared in the same manner as in Example 1, except that the polylactic acid resin-containing layer was formed to a thickness of 20 μm.

Example 4
A base paper was prepared in the same manner as in Example 1, except that the polylactic acid resin-containing layer was formed to a thickness of 40 μm.

Example 5
A base paper was prepared in the same manner as in Example 1, except that the paper weight was 150 g/ ^m2 .

Example 6
A base paper was prepared in the same manner as in Example 1, except that the paper weight was 450 g/ ^m2 .

Example 7
A base paper was prepared in the same manner as in Example 1, except that the paper was 150 g/ ^m2 and the polylactic acid resin-containing layer was 20 μm thick.

Example 8
A base paper was prepared in the same manner as in Example 1, except that the paper ^was 150 g/m2 and the polylactic acid resin-containing layer was 40 μm thick.

Example 9
A base paper was prepared in the same manner as in Example 1, except that the paper ^weight was 450 g/m2 and the thickness of the polylactic acid resin-containing layer was 20 μm.

Example 10
A base paper was prepared in the same manner as in Example 1, except that the paper was 450 g/ ^m2 and the polylactic acid resin-containing layer was 40 μm thick.

Example 11
A base paper was prepared in the same manner as in Example 1, except that the polylactic acid resin was "4060D" (manufactured by Nature Works, D-form content: 3 to 5% by mass), MFR: 10 (g/10 min-210°C, 2.16 kg), biodegradability: 53%).

Example 12
A base paper was prepared in the same manner as in Example 1, except that the polylactic acid resin was L175 manufactured by Total Corbion, D-form content: 1% by mass or less), MFR: 8 (g/10 min-210°C, 2.16 kg), and biodegradability: 11%).

Example 13
A base paper was prepared in the same manner as in Example 1, except that the polylactic acid resin was Total Corbion's LX175 (D-form content: 4% by mass or less), MFR: 6 (g/10 min·210° C., 2.16 kg), and biodegradability: 21%).

Comparative Example 1
A base paper was prepared in the same manner as in Example 1, except that the thickness of the polylactic acid resin-containing layer was 5 μm.

Comparative Example 2
A base paper was prepared in the same manner as in Example 1, except that the polylactic acid resin-containing layer was formed to a thickness of 60 μm.

Comparative Example 3
A base paper was prepared in the same manner as in Example 1, except that the paper weight was 100 g/ ^m2 .

Comparative Example 4
A base paper was prepared in the same manner as in Example 1, except that the paper weight was 550 g/ ^m2 .

Comparative Example 5
A single piece of paper measuring 243 cm long x 184 cm wide and having a basis weight of 260 g/ ^m2 was used for the test. The biodegradability of the single piece of paper was 78%.

Test Example 1
A blank sheet was obtained by punching the base paper of each Example and Comparative Example with a Thomson blade. This blank sheet was used to produce a paper container for curry dishes as shown in Figure 5 by a press molding method. Figure 5A is a photograph of the entire container, Figure 5B is a photograph of the container viewed from directly above, and Figure 5C is a photograph of the container viewed from directly to the side.

The containers were designed to be large enough to hold 150 g of commercially available white sauce to be used in the heat resistance evaluation test described below. In each case, the containers were molded so that the polylactic acid resin-containing layer was located on the inner surface (content-filled side) of the container. The base paper or its containers of each Example and Comparative Example were evaluated for (1) heat resistance, (2) adhesive strength, (3) moldability, and (4) stability and decomposability. The evaluation results are shown in Table 1. The evaluation methods are as follows.

(1) Heat resistance A container was filled with 150 g of commercially available white sauce (manufactured by Heinz) and heated in a Sharp microwave oven (model number: RE-MA1-N) at 600 W for 3 minutes. After heating, the white sauce was removed from the container and visually checked for the presence or absence of boiling of the polylactic acid resin-containing layer of the container or peeling from the paper substrate. Those that did not show boiling or peeling from the paper substrate were marked with "○", and those that showed boiling or peeling from the paper substrate were marked with "×". Here, "boiling" refers to the phenomenon in which the polylactic acid resin-containing layer cannot withstand the heat generated by the white sauce when heated in a microwave oven, melts, and locally swells.

(2) Adhesive strength The base paper was cut into a width of 50 mm and a length of 150 mm, and a 180° peel test was performed with an autograph (R2KN-B) manufactured by Japan Measurement Systems Co., Ltd., with a gauge length of 200 mm and a peel speed of 100 mm/min. Those that did not peel between the paper layers in the paper substrate itself were marked as "x", and those that peeled between the paper layers were marked as "o". That is, the "x" means that the polylactic acid resin-containing layer and the paper substrate peeled between before the paper substrate itself peeled (broke), and the adhesion between the polylactic acid resin-containing layer and the paper substrate is low. On the other hand, the "o" means that the paper substrate itself peeled (broke) before peeling between the polylactic acid resin-containing layer and the paper substrate, and the adhesion between the polylactic acid resin-containing layer and the paper substrate is high.

(3) Moldability The presence or absence of pinholes or tears was confirmed by spraying the inside surface of the container with Ageless Seal Check Liquid manufactured by Mitsubishi Gas Chemical Company, Inc. Three minutes after spraying the Ageless Check Liquid, the back surface of the container was visually inspected. If the Ageless Check Liquid had not penetrated the container, it was marked with "○" and if it had penetrated the container, it was marked with "×".

(4) Stability and decomposability Using a biodegradation measuring device (model: MODA-CS, manufactured by Yawata Bussan), the amount of _CO2 generated (g), which indicates decomposability, was measured for 12 days in accordance with the biodegradability test specified in the Japanese Industrial Standards JIS K6953-1 and -2. The measurement sample used was a film (30 μm) of polylactic acid resin alone. The measurement procedure was to knead 10 g of polylactic acid resin cut to 3.5 mm x 3.5 mm into 500 g of compost, and to carry out the test according to the method of the above JIS standard.
(4-1) Stability: Products with a _CO2 emission (120 hours) of 10 g or less after 5 days of testing were rated as "Good," and products with a CO2 emission of more than 10 g were rated as "Poor." Since the maximum expiration date of food generally contained in a container is about 5 days, products with a _CO2 emission of more than 10 g may decompose too quickly and may not be practically suitable for use as a food container.
(4-2) Degradability: When the amount of _CO2 generated after 12 days of testing was 10 g or more and 20 g or less, it was marked as "Good", and when the amount of CO2 generated was less than 10 g or more than 20 g, it was marked as "Poor". When the amount of _CO2 generated was less than 10 g, the degradability was impaired, and when the amount of _CO2 generated was more than 20 g, it may not be practically suitable as a food container as mentioned above.

As is clear from the results in Table 1, the biodegradable paper container of the present invention has good heat resistance, even though the base paper is a laminate of a polylactic acid resin-containing layer/paper base material, and the adhesiveness between the paper base material and the polylactic acid resin-containing layer is good. It can also be seen that excellent containers such as those in each Example can be efficiently manufactured by press molding. In particular, it can be seen that Examples 1 to 11, which use a relatively high polylactic acid resin with a biodegradability of about 30 to 60%, also show good results in terms of stability and decomposability. That is, it can be seen that the amount of _CO2 generated in 5 days according to the biodegradability test specified in JIS K6953-1 and -2 is 10 g or less, and the amount of _CO2 generated in 12 days is 10 to 20 g, which is suitable for disposable containers and the like.

Claims (6)

A container comprising a laminate including a paper base material and a polylactic acid resin-containing layer on one or both sides of the paper base material,
(1) The basis weight of the paper base material is 150 to 500 g/ ^m2 ;
(2) The thickness of the polylactic acid resin-containing layer is 10 to 55 μm,
(3) The polylactic acid resin contained in the polylactic acid resin-containing layer has a biodegradability of 30 to 70%;
(4) The content of the polylactic acid resin in the polylactic acid resin-containing layer is 98 to 100% by mass.
A biodegradable paper container characterized by the above. The biodegradable paper container according to claim 1, wherein the polylactic acid resin has a copolymer composition of 1 to 10% by weight of D-lactic acid and the remainder of L-lactic acid. 3. The biodegradable paper container according to claim 1 or 2, which is subject to heating in a microwave oven. The biodegradable paper container according to any one of claims 1 to 3, wherein the polylactic acid resin-containing layer is laminated on at least the inner surface of the container. The biodegradable paper container according to any one of claims 1 to 4, characterized in that the container is composed of a) a bottom portion, b) a side wall portion that is connected to the periphery of the bottom portion and rises upward, c) a flange portion that is connected to the upper end of the side wall portion and extends in a substantially horizontal direction, and d) a rolled edge portion that is connected to the outer periphery of the flange portion. A method for producing a biodegradable paper container, comprising the steps of:
A method for producing a biodegradable paper container, comprising: (1) a step of laminating a composition containing 98 to 100% by mass of a polylactic acid resin having a biodegradability of 30 to 70% on at least one surface of ^a paper base material having a basis weight of 150 to 500 g/m2 using a T-die extruder to obtain a laminate having a thickness of 10 to 55 μm; and (2) a step of forming the laminate into a container shape having a recess by press molding.