WO2007088833A1

WO2007088833A1 - Process for thermoforming biodegradable laminated sheets

Info

Publication number: WO2007088833A1
Application number: PCT/JP2007/051445
Authority: WO
Inventors: Kanji Yoshimura; Juichi Wakabayashi; Norio Ozawa; Takehisa Suzuki
Original assignee: Yoshimura Kasei Co., Ltd.; Kureha Corporation
Priority date: 2006-01-31
Filing date: 2007-01-30
Publication date: 2007-08-09
Also published as: JPWO2007088833A1; TW200744823A

Abstract

A thermoforming process for shaping a composite material obtained by laminating polylactic acid and polyglycolic acid, wherein the biodegradable resins can be efficiently enhanced in gas barrier properties and heat resistance in a short time without being impaired in the durability in service. A process for thermoforming biodegradable laminated sheets which comprises laminating a polyglycolic acid film with a polylactic acid film on either or both sides of the polyglycolic acid film to prepare a biodegradable laminated sheet, preheating the laminated sheet to 60 to 160°C, pressing a metal mold heated to 90 to 160°C against the laminated sheet, and keeping the resulting system as such for 3 to 60 seconds to conduct both the forming of the sheet by hot pressing and the crystallization of the polyglycolic acid film constituting the laminate. According to the process, a biodegradable laminated sheet having prescribed layer constitution is subjected to prescribed preheating and then brought into contact with a metal mold under pressing, whereby the crystallization of the polyglycolic acid film is conducted more efficiently in the process than in a dry-heat process, which makes it possible to enhance the gas barrier properties and the heat resistance in a short time.

Description

Specification

Thermoforming method of biodegradable laminated sheet

Technical field

The present invention relates to a thermoforming method for a biodegradable laminated sheet in which a polyglycolic acid-based resin and a polylactic acid-based resin are laminated and integrated.

Background art

[0002] Polylactic acid is biodegradable by being decomposed by microorganisms and enzymes to become harmless to the human body, becoming lactic acid, carbon dioxide and water, and has attracted attention as an alternative to medical materials and general-purpose resins. When used as a container material prepared to maintain strength and decompose naturally after use, it can be expected to reduce the amount of used plastic discarded.

[0003] However, if a plastic container is molded only from polylactic acid, it becomes inferior in heat resistance and mechanical strength. For example, when hot water is poured to warm food as a container for food, the container softens and deforms. The trouble which will be done also arises.

[0004] In addition, polylactic acid has low oxygen gas noreia, and therefore, when used as a food container that requires oxygen gas noreia, for example, it becomes a container unsuitable for long-term storage of food. Furthermore, since polylactic acid has a low water vapor property, when used in a container such as a dry food, it has a drawback that it is suitable for long-term storage due to moisture absorption or the like.

[0005] On the other hand, polyglycolic acid is known as a biodegradable resin, and has excellent noria properties such as oxygen gas barrier properties, carbon dioxide gas noria properties, and water vapor noria properties, as well as heat resistance and mechanical strength. As a packaging material, it is used alone or in combination with other resin materials.

[0006] In addition, when a container is formed by laminating a polylactic acid-based biodegradable resin sheet and paper or the like, the polylactic acid-based resin can be stretched well without forming wrinkles at the edges of the container. In addition, there is known a method of pressure forming or vacuum forming at a mold temperature of 100 to 140 ° C. (Patent Document 1).

[0007] Patent Document 1: Japanese Patent Laid-Open No. 2003-276078

Disclosure of the invention Problems to be solved by the invention

[0008] In the invention described in Patent Document 1, the conditions for improving the physical properties of polydaricholic acid are not specifically shown, as it does not improve the quality of other materials laminated to polylactic acid. .

Therefore, the first problem of the present invention is to efficiently and quickly heat set (crystallization treatment) as a method for forming a composite material in which polylactic acid and polyglycolic acid are laminated by solving the above-mentioned problems. The same shall apply hereinafter) to improve the noria property and also to improve the heat resistance.

The second object of the present invention is to obtain a biodegradable laminated sheet and a biodegradable container that have high noria properties and heat resistance that are obtained by such thermoforming. Means for solving the problem

[0010] In order to solve the above-described problems, in the present invention, a biodegradable laminated sheet in which a polylactic acid polymer layer is laminated and integrated on one side or both sides of a polyglycolic acid polymer layer is provided. The laminated sheet is preheated to 60 to 160 ° C., and then the mold heated to 90 to 160 ° C. is pressed against the laminated sheet and held as it is for a predetermined time. This is a method for thermoforming a biodegradable laminated sheet comprising crystallizing the polyglycolic acid polymer layer of the laminated sheet.

[0011] According to the thermoforming method of the present invention described above, the mold temperature is set to 90 ° C during the pressure forming of the biodegradable laminated sheet in which the polyglycolic acid resin and the polylactic acid resin are laminated and integrated. By setting the biodegradable laminated sheet having a predetermined layer structure to this mold at a temperature of ~ 160 ° C and pressing it after a predetermined preheating, an efficient heat setting can be performed compared to the dry heat method. Can be shortened.

In order to obtain a method with high thermoforming efficiency, it is preferable that the predetermined time for keeping the heated mold pressed against the biodegradable laminated sheet as it is is 3 to 60 seconds.

[0012] A biodegradable container or other form of biodegradable mature molded body comprising the biodegradable laminated sheet obtained as described above is a mature molded body such as a dry heat type heat-set container, Heat resistance and strength are improved compared to containers molded with only a single layer of lactic acid, and both strength and noria are significantly improved. The invention's effect

[0013] The thermoforming method of the present invention is biodegradable into a mold adjusted to a predetermined temperature at the time of pressure forming of a biodegradable laminated sheet in which a polyglycolic acid-based resin and a polylactic acid-based resin are laminated and integrated. Since the laminated sheet is pressed after a predetermined preheating, the biodegradable resin increases the barrier properties efficiently and in a short time without impairing the durability during use, and also improves the heat resistance. There is an advantage of a molding method. Further, according to this thermoforming method, it is possible to perform heat setting more efficiently than the dry heat method, and it is possible to produce a molded body such as a container that is excellent in noirality and heat resistance.

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] The polyglycolic acid polymer (also referred to as polyglycolic acid resin) used in the present invention has a repeating unit (glycolic acid unit) represented by the formula — (— 0—CH—CO 2) — Contains

2

It consists of a homopolymer or a copolymer.

[0015] The content of the repeating unit represented by the above formula in the polyglycolic acid polymer is 50% by weight or more, preferably 60% by weight or more, more preferably 80% by weight or more, The upper limit is 100 weight percent. If the content ratio of the repeating unit represented by the above formula is too small below the predetermined range, the barrier properties and heat resistance are reduced.

[0016] In addition to the glycolic acid unit represented by the above formula, the polyglycolic acid resin contains a polymerization unit of a comonomer copolymerizable with glycolic acid to form a glycolic acid copolymer. be able to.

[0017] Comonomers include ethylene oxalate (ie, 1,4 dioxane-1, 2, 3 dione), lactides, and ratatones (eg, propiolatatatone, petit-latataton, pivalolatatone, valeratalatatane, methylvalerolatatone, strength Cyclic monomers such as prolatatatone), carbonates (such as trimethyl carbonate), ethers (such as 1,3 dioxane), ether esters (such as dioxanone), amides (such as prolatatam); lactic acid, 3- Hydroxycarboxylic acids such as hydroxypropanoic acid, 4-hydroxybutanoic acid and 6-hydroxycaproic acid or alkyl esters thereof; aliphatic diols such as ethylene glycol and 1,4 butanediol and fats such as succinic acid and adipic acid Group carboxylic acids or Can be used in substantially equimolar mixtures with their alkyl esters.

[0018] In order to adjust the crystallinity of the polyglycolic acid resin, a relatively small amount of other thermoplastic resin can be mixed to such an extent that the effects of the present invention are not impaired.

[0019] The other resin used in this case is preferably biodegradable, and of course, for the purpose of adjusting the molding processability and the physical properties of the sheet or molded product, An additive such as an agent, an inorganic filler, and an ultraviolet absorber, a modifier, and the like can also be added.

[0020] The glycolic acid (co) polymer used in the present invention has a melt viscosity of 100 to 10,000 Pa'sec, more preferably 300 to 8000 Pa 'measured under conditions of a temperature of 270 ° C and a shear rate of 120 sec- ^1. sec, particularly preferably in the range of 400 to 5000 Pa ′ sec.

Next, the polylactic acid polymer used in the present invention is polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid, or a mixture of these polymers.

[0022] Examples of lactic acid include L-lactic acid, D-lactic acid, and mixtures thereof. Other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid. Typical examples include valeric acid and 6-hydroxycaproic acid.

[0023] The polylactic acid polymer layer can be mixed with another polymer material in an amount that does not impair the effects of the present invention. Of course, it is preferable that the other resin in this case is biodegradable, and the molding cacheability of the polylactic acid polymer and the physical properties of the sheet-molded body are as follows. Additives such as plasticizers, lubricants, inorganic fillers, UV absorbers, modifiers, etc. may be added for the purpose of adjusting the viscosity.

[0024] In addition, as the polylactic acid polymer layer in the present invention, a regrind (recovered, reground) product of the hard resin molding container of the present invention can be used.

[0025] The layer structure of the biodegradable laminated sheet according to the present invention is at least two or more layers composed of the above-mentioned A layer which is a polydaricholic acid polymer and a B layer which is mainly composed of a polylactic acid polymer. Is required, and preferably has a BZAZB configuration.

[0026] The specific configuration is not limited to this, but may be BZAZBZAZB or the like. In addition, a C layer comprising the regrind (collected and reground) of the hard resin container of the present invention as a main component is laminated, and C / A / C, B / C / A / C / B, B / A / C , B / A / C / B And so on.

[0027] In any of the above cases, an adhesive layer can be appropriately interposed between the layers. Examples of the adhesive layer used include maleic anhydride-modified polyolefin resin (Mitsubishi Chemical Corporation: Modic S525, XS533, F513, F533, Mitsui Chemicals: Admer NF550), glycidyl group-containing ethylene copolymer (Nippon Oil Co., Ltd.). Chemical: Lettuce Pearl RA3150, Sumitomo Chemical Co., Ltd .: Bondfast 2C, E, B), Thermoplastic polyurethane (Kurarene clay: Chlamylon 1195L), Polyamide 'Ionomer (Mitsui DuPont: AM7926), Poly Acrylic imide resin (Rohm 'And' Haas Co., Ltd .: XHTA).

[0028] These are inferior in biodegradability. The thickness of the adhesive layer is 0.5 ~: about LO / zm, which is very thin and the environmental load can be reduced by the small amount of use. Is possible. In particular, an adhesive resin having good biodegradability is preferably used in the present invention.

[0029] In the present invention, a biodegradable laminate sheet obtained by laminating and integrating a polylactic acid polymer layer on one side or both sides of a polyglycolic acid polymer layer composed of the above materials. Can be produced by a commonly used well-known method.

[0030] For example, a method of co-extrusion using a plurality of extruder force feed block methods or a multi-hold method, or laminating a single layer sheet having a polyglycolic acid polymer force and a single layer sheet having a polylactic acid polymer force By this method, a multi-layer structure can be formed.

[0031] The thickness of the biodegradable laminated sheet is not particularly limited and is appropriately selected according to the desired desired performance. For example, when a biodegradable laminated sheet is used as a single material for a hard container, the total thickness after forming the container must be 100 m or more. In case of reinforcement with the like, the total thickness after forming the container can be 100 μm or less.

[0032] The biodegradable laminated sheet obtained in this way can be formed into a desired molded body using thermoforming such as pressure forming or vacuum forming. Preferably, the biodegradable laminated sheet is heated to 60 ° C. to 160 ° C. with a heater, then pressed against a mold heated to 90 to 160 ° C., then cooled and thermoformed. [0033] In consideration of the crystallization time of the polyglycolic acid polymer, the time for pressure contact with the mold during thermoforming is preferably 1 second to 10 minutes, more preferably 3 seconds to 60 seconds. It is. When the mold temperature is 150 ° C or higher, it may be difficult to release the mold, so the time for pressure contact with a general mold is preferably about 3 seconds (eg 3-4 seconds).

Example

[0034] In the following examples, a preheated biodegradable laminated sheet is pressed against a mold at a predetermined temperature, and a container is thermoformed while being heat-set, that is, crystallized by pressure forming, as a comparative example. Compared a polylactic acid single layer container with a molded heat set process without heat setting or with dry heat (that is, heating in a non-pressurized state).

[0035] [Examples 1 to 12]

As polyglycolic acid (PGA), temperature 270 ° C, those of the homopolymer of melting viscosity measured at a shear rate 120 sec ^_1 is 900Pa'sec (glass transition temperature 38 ° C, melting point 221 ° C) ((Ltd.) Kureha Manufactured by PGA). A material obtained by adding 0.1% by weight of a heat stabilizer (Asahi Denshi Kogyo Co., Ltd .: ADK STAB AX-71) to 100 parts by weight of this polyglycolic acid was used as an extrusion molding material.

[0036] As polylactic acid, polylactic acid manufactured by Unitica Co., Ltd. having a melt viscosity of 1300 Pa'sec measured at a temperature of 200 ° C and a melting point of 162 ° C was used.

[0037] Using these resin materials, extrusion molding was performed by a T-die method to produce a multilayer sheet. The layer structure was polylactic acid (275 μm) Z polyglycolic acid (50 μm) Z polylactic acid (275 μm).

[0038] The upper and lower surfaces of this sheet were heated in a non-pressurized state by applying the heating wire of an electric heater set at 130 ° C, and the mold temperature shown in Table 1 for the sheet softened in the following! A female mold heated to 90 ° C. to 150 ° C. under the conditions of the heat setting time was applied for 3 to 10 seconds, and the cup type container was subjected to crystallization treatment simultaneously with pressure forming to obtain a biodegradable cup type container.

[0039] (1) Formability, (2) Density (as a measure of crystallinity), (3) Heat resistance, (4) Oxygen The gas permeability was evaluated.

[0040] (1) Formability

Moldability by mold temperature and time for pressure contact with mold (molding container from mold The releasability was confirmed. The evaluation criteria are as follows: ◯: released, Δ: difficult to release, X: not released.

[0041] (2) Density

Measured by the density gradient tube method in accordance with JIS-K7112. A mixture of carbon tetrachloride and 1,2-dichloroethane was used as the immersion liquid.

[0042] (3) Heat resistance test

i) Shrinkage of container with hot water

100 ° C hot water was poured into the container, and the container was observed for shrinkage after 30 seconds. Evaluation was performed according to the following criteria. ○: No contraction, partial contraction, X: Large contraction

ii) Pouring hot water and falling body test

Pour hot water of 100 ° C into the container, and after 30 seconds, drop the container onto the concrete from a height of 50 cm and observe the deformation. Evaluation was performed according to the following criteria.

○: No deformation, Δ: Partial deformation, X: Large deformation

[0043] (4) Oxygen gas permeability

Using OX-TRAN2Z20 manufactured by Modern Control Co., in accordance with JIS-K7126B, measurement was performed while maintaining the inside of the container at a temperature of 23 ° C and a relative humidity of 80% at a temperature of 23 ° C and a relative humidity of 50%.

[0044] [Comparative Example 1]

A cup was thermoformed in the same manner as in Example 1 except that the temperature of the female mold applied in the pressure forming in Example 1 was 30 ° C. or lower and the heating time was 10 seconds. The evaluation tests (1) to (4) were performed on the obtained cup-type container.

[0045] [Comparative Example 2]

While the cup molded in Comparative Example 1 was fixed so as to maintain its shape, it was heat-set for 10 seconds by a dry heat method at 100 ° C. oven.

[0046] [Comparative Example 3]

While the cup molded in Comparative Example 1 was fixed so as to maintain its shape, heat setting was performed for 1 minute by a dry heat method at 100 ° C. in an oven.

[0047] [Comparative Example 4] A cup was obtained in the same manner as in Example 1 except that the polyglycolic acid layer was removed in Example 1.

[0048] For Comparative Examples 1 to 4 obtained as described above, the moldability was confirmed by evaluation tests (1) to (4), and the results are shown in Tables 1 and 2.

[0049] Details of the evaluation tests performed on the examples and comparative examples are as follows.

For Examples 1-12, the moldability was confirmed, and for the cups obtained in Examples 1-10, Comparative Example 1, Comparative Example 2, and Comparative Example 3, the density of the polyglycolic acid layer was measured. The results are also shown in Table 1.

Examples 1 to: The cup-type containers obtained in LO and Comparative Examples 1 to 4 were subjected to a heat resistance test, and the results are also shown in Table 1.

Example 6 (mold temperature 100 ° C, time 10 seconds), oxygen gas permeability was measured with the cups obtained in Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, and the results were obtained. Is also shown in Table 2.

[0050] [Table 1]

[0051] [Table 2] Oxygen gas permeability

(cm ³ / cup-day-atm)

Example 6 0. 0 1 7

Comparative Example 1 0. 0 2 4

Comparative Example 2 0. 0 2 5

Comparative Example 3 0. 0 2 0

Comparative Example 4 0.9

As is clear from the results in Tables 1 and 2, regarding moldability, the mold temperature of 150 ° C. was close to the melting point of polylactic acid, so that the mold release was poor when the pressure contact time was long.

[0053] Regarding the density, when comparing the density up to Example 1 to LO with Comparative Example 1 (without heat setting), it can be seen that the polyglycolic acid layer is sufficiently crystallized by heat setting. . Compared with Comparative Examples 2 and 3 (dry heat type), the density value is large and the crystallinity is high.

[0054] Regarding the mold temperature, the higher the temperature, the higher the density. Regarding the time, it is obvious that a heat setting of 3 seconds is sufficient.

[0055] With respect to heat resistance, it can be seen from Table 1 that Examples 1 to: LO is sufficiently crystallized by heat setting, so that there is no shrinkage due to hot water. At a mold temperature of 90 ° C, some deformation is observed due to the falling body after pouring hot water. This is thought to be due to the difference in crystallinity shown in the density results. On the other hand, in Comparative Examples 1 to 4, shrinkage due to hot water was observed.

[0056] With respect to the oxygen gas permeability, the results of Example 6 and Comparative Example 4 in Table 2 indicate that the oxygen gas normality is greatly improved as compared with the polylactic acid monolayer. As for heat setting, oxygen gas in Example 6 compared to no heat set (Comparative Example 1), dry heat type heat set for 10 seconds (Comparative Example 2), and dry heat type heat set for 1 minute (Comparative Example 3). It can be seen that the performance is improved.

In addition, the oxygen gas normality of Example 6 is an oxygen gas permeability of 0.017 (cm ³ Zcup 'day atm), which can withstand use even when used in storage containers for foods, etc. As mentioned above, hot water of 100 ° C was poured, but it did not shrink and was not deformed. Therefore, the thermoforming method of the biodegradable laminated sheet shown in the examples is oxygen gas permeability 0. 017 (cmVcup · day · atm) Excellent gas barrier that requires less than or equal to 017 (cmVcup · day · atm).

From the above, the laminated sheet is preheated to 60 to 160 ° C., and then the mold heated to 90 to 160 ° C. is pressed against the laminated sheet and kept as it is for a predetermined time. It was confirmed that the polyglycolic acid polymer layer of the laminated sheet was crystallized simultaneously with the molding, and the crystallinity, heat resistance, and oxygen gas permeability were improved.

Claims

The scope of the claims

[1] A biodegradable laminate sheet in which a polylactic acid polymer layer is laminated and integrated on one or both sides of the polyglycolic acid polymer layer is provided, and this laminate sheet is preheated to 60 to 160 ° C. Next, by pressing the mold heated to 90 to 160 ° C. against the laminated sheet and holding it for a predetermined time, the polyglycolic acid polymer of the laminated sheet is simultaneously formed with the hot pressing. A method for thermoforming a biodegradable laminated sheet comprising crystallizing a layer.

[2] The method for thermoforming a biodegradable laminated sheet according to claim 1, wherein the predetermined time for holding the mold in pressure contact is 3 to 60 seconds.

[3] The thermoforming method according to claim 1 or 2, comprising a biodegradable laminated sheet in which a polylactic acid polymer layer is laminated on one side or both sides of a polyglycolic acid polymer layer and integrated. A biodegradable mature molded article obtained by crystallizing a polydalicolate polymer layer.

[4] The thermoforming method according to claim 1 or 2 for the biodegradable laminated sheet in which the polylactic acid polymer layer is laminated and integrated on one side or both sides of the polyglycolic acid polymer layer. A biodegradable container comprising, as a constituent material, a biodegradable laminated sheet obtained by crystallizing a polydalicolate polymer layer.