JP5877111B2 - Manufacturing method of polylactic acid resin foam sheet for thermoforming, and manufacturing method of sheet molded product - Google Patents

Description

  The present invention relates to a method for producing a polylactic acid resin foam sheet for thermoforming, and a method for producing a sheet molded product.

Conventionally, strip-shaped foam sheets made by extruding and foaming thermoplastic resins such as polystyrene-based resins, polyolefin-based resins, and polyester-based resins together with hydrocarbon-based foaming agents from circular dies have been widely used as raw materials for sheet molded products. ing.
In recent years, due to the growing demand for environmental considerations, the use of polylactic acid resins has been expanded in place of general polyester resins, and the use range of polylactic acid resin foam sheets has been expanded.

  The polylactic acid-based resin foam sheet tends to form open cells during extrusion foaming, and tends to be difficult to obtain a foam having a desired expansion ratio. Studies have been conducted to obtain a resin foam sheet.

JP 2006-224628 A

By the way, in the polylactic acid-based resin foam sheet after extrusion foaming, hydrocarbons such as butane used as a foaming agent usually remain to some extent in the bubbles or the bubble film.
This remaining foaming agent exhibits a plasticizing effect when thermoforming a polylactic acid resin foamed sheet, but on the other hand, if the foaming agent remains in the sheet molded product obtained by thermoforming, this sheet molded product There is a possibility that the plasticizing effect will be exerted and thermal deformation will be easily caused.
Also, considering the storage of a certain amount of sheet molded products that may generate hydrocarbon gas, the foaming agent is left in the polylactic acid resin foam sheet or sheet molded product for thermoforming. It is hard to say that it is always a good thing.
Even when the foaming agent is other than hydrocarbon, it is better not to leave the foaming agent in the polylactic acid resin foam sheet for thermoforming and sheet molded products in order to prevent odor and prevent changes over time in properties. There is a good case.

In consideration of such matters, it is conceivable that the polylactic acid resin foam sheet has an open cell ratio of a certain level or more to promote the dissipation of the foaming agent during thermoforming.
However, if a polylactic acid resin foam sheet having a high open cell ratio is formed by extrusion foaming, it becomes difficult to obtain a foam having a desired expansion ratio.

In other words, the conventional polylactic acid resin foam sheet for thermoforming has a problem that it is substantially difficult to obtain an open cell ratio of a certain level or more, and it is difficult to obtain a sheet molded product with a low residual amount of foaming agent. doing.
It is an object of the present invention to solve such problems, and makes it easy to adjust the open cell ratio of a polylactic acid resin foam sheet for thermoforming, and manufactures a sheet molded product with a low residual amount of foaming agent. It is an object of the present invention to provide a method for producing a sheet molded product that can be performed.

  In order to solve the above-mentioned problems, the present inventor has conducted intensive studies. As a result, the polylactic acid resin foamed sheet is formed after extrusion foaming, and the polylactic acid resin foamed sheet is formed at or above the crystallization start temperature. It was found that the open cell ratio can be increased as compared with before heating, and that the open cell ratio can be easily adjusted by a relatively simple method, and the present invention has been completed. .

That is, the present invention relating to a method for producing a thermoforming polylactic acid resin foam sheet for solving the above-mentioned problems is a sheet production for producing a polylactic acid resin foam sheet by extruding and foaming a polylactic acid resin together with a foaming agent. A method for producing a thermoforming polylactic acid resin foamed sheet by performing a process to produce a polylactic acid resin foamed sheet for thermoforming, wherein the polylactic acid resin foamed sheet obtained by the sheet forming step is Further performing a heat treatment step of heating the lactic acid resin to a temperature higher than the crystallization start temperature to improve the open cell ratio of the polylactic acid resin foam sheet ,
In the heat treatment step, the heating is performed until the open cell ratio of the polylactic acid-based resin foam sheet is 25% or more and 60% or less and the heat of crystallization of the polylactic acid-based resin foam sheet is 1 mJ / mg or less. It is characterized by.

In addition, the present invention relating to the sheet molded product manufacturing method is a method of thermoforming a polylactic acid resin foam sheet for thermoforming produced by performing a sheet forming step of extruding and foaming a polylactic acid resin together with a foaming agent to form a sheet. A sheet molded product manufacturing method for producing a product, wherein the polylactic acid resin foam sheet obtained in the sheet forming step is used as the polylactic acid resin foam sheet for thermoforming, and the crystallization start temperature of the polylactic acid resin is obtained. Using the heat-treated polylactic acid-based resin foam sheet obtained by further performing the heat-treatment step for improving the open cell ratio of the polylactic acid-based resin foam sheet by heating as described above, the polylactic acid-based resin is used in the heat treatment step. open cell ratio of the foam sheet becomes 60% or less than 25%, and the crystallization heat of the polylactic acid-based resin foam sheet that you implement the heating until the following 1 mJ / mg It is a symptom.

In the present invention, the polylactic acid-based resin foam sheet obtained by the sheet forming step of producing a polylactic acid-based resin foamed sheet by extruding and foaming a polylactic acid-based resin together with a foaming agent is used as the polylactic acid-based resin crystallization start temperature. The open cell ratio of the polylactic acid resin foam sheet for thermoforming can be adjusted by a simple operation of heating as described above.
Therefore, in the sheet forming step, it is possible to easily obtain a desired foaming ratio by reducing the open cell ratio to some extent and easily produce a sheet molded product having a low residual foaming agent. .

The schematic block diagram which showed typically the equipment structure used for the manufacturing method of a polylactic acid-type resin foam sheet.

The preferred embodiments of the present invention will be described below.
In the method for producing a thermoforming polylactic acid-based resin foam sheet in the present embodiment, a sheet forming step of producing a polylactic acid-based resin foam sheet by extruding and foaming a polylactic acid-based resin together with a foaming agent is carried out, and the sheet formation is performed. A heat treatment step is further performed in which the polylactic acid resin foam sheet obtained in the step is heated to a temperature higher than the crystallization start temperature of the polylactic acid resin to improve the open cell ratio of the polylactic acid resin foam sheet.

The polylactic acid resin used in the sheet forming step is not particularly limited, and a polymer containing 50 mol% or more of lactic acid component units can be employed.
The polymer includes (1) a polymer of lactic acid, (2) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, (3) a copolymer of lactic acid, an aliphatic polyhydric alcohol and an aliphatic polycarboxylic acid, (4) Copolymer of lactic acid and aliphatic polyhydric carboxylic acid, (5) Copolymer of lactic acid and aliphatic polyhydric alcohol, (6) Mixture by any combination of (1) to (5) be able to.
Specific examples of the lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid or their cyclic dimer L-lactide, D-lactide, DL-lactide, or a mixture thereof. .

Examples of the polylactic acid-based resin include those in which a D-form and an L-form of lactic acid are copolymerized, the D-form ratio of the copolymer is 0.5 to 5 mol%, and the melting point is The thing of 130-170 degreeC is preferable.
Such a polylactic acid-based resin is preferred because the foamability of the polylactic acid-based resin composition is foamed, the thermoformability of the resulting polylactic acid-based resin foamed sheet, and the polylactic acid-based resin foamed sheet. It is because the heat resistance of the sheet molded product obtained by thermoforming can be made excellent.

A polylactic acid resin having a higher melt tension is preferable for forming a good polylactic acid resin foamed sheet by extrusion foaming.
However, polylactic acid resins exhibiting particularly excellent crystallinity generally have a low melt tension. Therefore, the polylactic acid resin has a low melt tension, so that it can be crosslinked by a method such as chemical crosslinking or electron beam crosslinking, or mixed with a high molecular weight component. Those having an increased melt tension and improved extrusion foamability can be suitably used.
Examples of such a polylactic acid resin having improved melt tension and excellent crystallinity are commercially available from Unitika, trade names “Terramac HV6250H”, “Terramac HV8250H”, Nature Works, trade name “INGEO8251D”, and the like. Product can be adopted.

In the polylactic acid-based resin foam sheet produced in the sheet forming step, a ratio other than the polylactic acid-based resin is such that the proportion of the total with the polylactic acid-based resin is more than 0% by mass and 50% by mass or less. A thermoplastic resin may be included.
Specific examples of thermoplastic resins other than polylactic acid resins that can be included include polyethylene resins, polypropylene resins, polystyrene resins, polyester resins other than polylactic acid resins, and the like.
In this embodiment, it is preferable to contain a thermoplastic elastomer in the polylactic acid resin composition in that the impact resistance of the polylactic acid resin foam sheet can be improved.
Examples of the thermoplastic elastomer include olefin-based elastomers, styrene-based elastomers, acrylic-based elastomers, and ester-based elastomers. If they are included in the polylactic acid-based resin foam sheet, among them, the phase with the polylactic acid-based resin is included. A highly soluble acrylic elastomer, acid-modified styrene elastomer, and ester elastomer are preferred.
Specifically, commercially available products such as Mitsubishi Rayon Co., Ltd., trade name “Metablene W-600A”, Asahi Kasei Co., Ltd., trade name “Tough Tech MP10”, NOF Corporation, trade name “Nofalloy TZ810” are suitably used. be able to.

As the blowing agent, hydrocarbons such as lower alkanes such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane, and ethers such as dimethyl ether are easy to obtain a polylactic acid resin foam sheet having a high expansion ratio. And physical foaming agents such as halogenated hydrocarbons such as methyl chloride and ethyl chloride, and inorganic gases such as carbon dioxide.
Among these, normal butane, isobutane, dimethyl ether, and carbon dioxide are preferable. As the foaming agent, in addition to the above physical foaming agent, a chemical foaming agent, or a physical foaming agent and a chemical foaming agent may be used in combination.
If this foaming agent is hydrocarbon type foaming agents, such as butane, for example, it can be used in the ratio of 1-10 mass parts with respect to 100 mass parts of polylactic acid-type resin.

As the bubble adjusting agent, for example, inorganic nucleating agents such as talc and silica, organic nucleating agents such as polytetrafluoroethylene, and the like can be suitably used.
In particular, talc and polytetrafluoroethylene are preferable from the viewpoint of easy adjustment of bubbles.
In addition, the bubble regulator may appropriately contain a fatty acid metal salt type bubble regulator such as calcium stearate.

  Furthermore, the polylactic acid-based resin composition for forming the polylactic acid-based resin foamed sheet may contain various additives such as a colorant, an antioxidant, and hydrolysis inhibition depending on the purpose.

In the sheet forming step, such a foaming agent or polylactic acid resin is melt-kneaded with an extruder and extruded and foamed from a circular die attached to the tip of the extruder to form a polylactic acid resin foam sheet. Can do.
In this sheet forming step, in order to easily produce a polylactic acid-based resin foam sheet having a desired expansion ratio, the ratio of the resin and the foaming agent is adjusted, and the open cell ratio is preferably 30% or less, preferably Is preferably subjected to extrusion foaming so that the open cell ratio is 20% or less.

  In addition, as the polylactic acid resin foamed sheet to be produced in this sheet forming step, a polylactic acid resin foamed sheet having a crystallinity of less than 40% by adjusting the cooling conditions for the polylactic acid resin foamed sheet immediately after extrusion is adjusted. It is preferable to form.

In addition, although the thickness, apparent density, average cell diameter, etc. of the polylactic acid-based resin foam sheet formed in the sheet forming step are arbitrary, for example, the thickness is preferably 0.5 to 7 mm, More preferably, it is 5 mm, and it is especially preferable that it is 1-4 mm.
This is because the sheet molded product obtained by setting the thickness of the polylactic acid resin foamed sheet to 0.5 mm or more can be made more reliably excellent in strength, and the polylactic acid resin This is because, by setting the thickness of the foam sheet to 7 mm or less, the thermoformability of the polylactic acid resin foam sheet is improved.

As for the apparent density is preferably 0.04~0.25g / cm ^3, more preferably 0.06~0.25g / cm ^3.
This is because when the apparent density of the polylactic acid-based resin foam sheet is 0.03 g / cm ³ or more, the thermoformability of the polylactic acid-based resin foam sheet becomes even better, and the mold surface of the mold can follow. This is because it is easy to obtain a sheet molded product having a desired shape, and the obtained sheet molded product can be excellent in strength.
Moreover, it is preferable to have such an apparent density as described above. By setting the apparent density of the polylactic acid resin foam sheet to 0.25 g / cm ³ or less, the polylactic acid resin foam sheet is thermoformed. This is because the obtained sheet molded product can be excellent in lightness, heat insulation, and buffering property.

Furthermore, the average bubble diameter is preferably 0.1 to 1 mm, more preferably 0.1 to 0.8 mm, and particularly preferably 0.1 to 0.6 mm.
This is because the average cell diameter of the polylactic acid-based resin foamed sheet is 0.1 mm or more, so that the continuous cell ratio during extrusion foaming of the polylactic acid-based resin foamed sheet can be reduced to easily obtain a desired thickness. This is to make it happen.
Moreover, by setting the average cell diameter of the polylactic acid-based resin foam sheet to 1 mm or less, the obtained sheet molded product can be made excellent in heat insulation, buffering property, and the like.

In addition, about the said crystallinity degree, it can measure by implementing heat flux differential scanning calorimetry.
Exemplifying a specific measurement method, heat flux differential scanning calorimetry (heat flux DSC) can be measured based on the heat flux differential scanning calorimetry described in JIS K7122-1987. Nanotechnology Co., Ltd. differential scanning calorimeter device “DSC6220 type” was used to fill a measurement container with 4 to 6 mg of a sample of a polylactic acid resin foam sheet, and a nitrogen gas flow rate of 25 mL / min and 2 ° C./min. The crystallization exotherm and the melting endotherm can be measured at a heating rate of 40 to 200 ° C., and the crystallinity can be determined by the following equation.

Crystallinity (%) = [Endotherm of melting (mJ) −Exotherm of crystallization (mJ)] / Heat of fusion of complete crystal (mJ) × 100 (%)

(However, the heat of fusion of complete crystals of polylactic acid resin is 93 mJ.)

  The amount of heat generated by crystallization is a value obtained by integrating the area between a straight line connecting the crystallization start temperature at which the DSC chart leaves the baseline and the crystallization end temperature at which the DSC chart returns to the baseline again, and the chart. The melting endotherm is also a value obtained by integrating the area between the chart and the line connecting the melting start temperature at which the DSC chart leaves the baseline and the melting end temperature at which the DSC chart returns to the baseline again.

The open cell ratio can be measured using, for example, an air comparison type hydrometer made by Tokyo Science Co., Ltd. From the volume (V) of the test piece of the polylactic acid resin foam sheet, the following formula Can be calculated based on

Open cell ratio (%) = (V ₀ −V) / V ₀ × 100

In the above formula, “V” is the volume (cm ³ ) of the test piece measured by the above method, and “V ₀ ” is the apparent volume of the test piece calculated from the outer dimensions of the test piece used for the measurement. (Cm ³ ).

  Furthermore, the apparent density is obtained by cutting out several 10 × 10 cm measurement samples from the polylactic acid resin foam sheet, measuring the thickness and mass of each sample, and calculating the arithmetic average of the densities calculated from the mass and volume of each sample. Can be determined.

Moreover, the average cell diameter of the said polylactic acid-type resin foam sheet can be measured based on the test method of ASTMD2842-69.
Specifically, the polylactic acid-based resin foam sheet is cut along MD (extrusion direction) and TD (width direction orthogonal to the extrusion direction), and the center part of each cut surface is a scanning electron microscope (Corporation). Hitachi S-3000N) zoomed in and changed the field of view to take two photos, printed the images on A4 paper, and three straight lines with a length of 60 mm on each image (MD: 2 The number of bubbles × 3 = 6 in total, TD: 2 × 3 = 6 in total) The average chord length (t) of bubbles from the average number of bubbles in each direction on this straight line The bubble diameter in each direction (MD direction, TD direction, VD direction) can be calculated from the average chord length by the following formula.

Average chord length: t = 60 (mm) / (number of bubbles × photo magnification)
Bubble diameter: D = t / 0.616 (mm)

In general, the bubble diameter is calculated by drawing a straight line parallel to MD for a cut surface cut along MD and parallel to TD for a cut surface cut along TD.
Furthermore, VD (thickness direction) can calculate a bubble diameter similarly to the above by drawing a straight line on one image each of MD and TD.
At this time, usually, the magnification is adjusted with the electron microscope so that there are 10 to 20 bubbles on the straight line, and when drawing the straight line, the straight line penetrates as much as possible without making point contact with the bubble. Please note that.
When some of the bubbles come into point contact with a straight line, the calculation is performed by including the bubbles in the number of bubbles, and further including the bubbles at both ends of the straight line in the number of bubbles.

The geometrical average value of the bubble diameter in the _MD (D _MD ), the bubble diameter in the _TD (D _TD ), and the bubble diameter in the _VD (D _VD ) thus obtained is calculated as the average bubble diameter of the polylactic acid resin foam sheet. can do.
That is, the average cell diameter of the polylactic acid resin foam sheet can be calculated by the following formula.

Average bubble diameter (mm) = (D _MD × D _TD × D _VD ) ^1/3

Next, the heat treatment step is performed so that the polylactic acid-based resin foam sheet formed in such a state is suitable for forming a sheet molded product with a reduced amount of foaming agent remaining.
In the heat treatment step, the polylactic acid resin foam sheet is heated by heating the polylactic acid resin foam sheet to a temperature higher than the crystallization start temperature of the polylactic acid resin constituting the polylactic acid resin foam sheet as described above. It improves the open cell ratio.

This heat treatment step is usually a method in which a heating element is brought into direct contact with the polylactic acid resin foam sheet obtained in the sheet forming step and heated to the crystallization start temperature or higher, and the crystal is formed by radiant heating like an infrared heater. Adopting a method of increasing the crystallization start temperature or higher, a method of increasing the polylactic acid resin foamed sheet to the crystallization start temperature or higher using a general air circulation type heating furnace, or a method of combining a plurality of these. Although it is possible to implement, in the present embodiment, it is preferable to employ the first method of bringing the heating element into contact.
In particular, a plurality of heating rolls heated to a temperature higher than the crystallization start temperature of the polylactic acid resin forming the polylactic acid resin foam sheet are provided on one side and the other side of the polylactic acid resin foam sheet. It is preferable to heat the both sides of the polylactic acid-based resin foamed sheet with this heating roll.

  A specific example in which the heat treatment step of such a polylactic acid resin foamed sheet is carried out continuously with the sheet forming step will be described with reference to FIG. 1. As shown in FIG. 1, the circular die 1 is attached to the tip portion. The polylactic acid resin composition is melted and kneaded by the tandem extruder 70 thus formed, and the polylactic acid resin foamed sheet 20 is extruded in a cylindrical shape from the annular discharge port of the circular die 1, and from the discharge port of the circular die 1. An outer peripheral surface of a cylindrical cooling mandrel 30 having a large diameter is applied to the polylactic acid resin foam sheet 20 from the inside, and the cylindrical polylactic acid resin foam sheet 20 is expanded and cooled by the circular die 1. The cooled polylactic acid resin foam sheet 20 is divided into two parts by a cutter, and a polylactic acid resin foam sheet 20 ′ opened so as to form a flat belt is disposed in the rear stage. The polylactic acid-based resin foamed sheet is wound around four heating rolls 40 arranged in a staggered manner on the top and bottom before winding by the winding roller 92 after winding by the winding roller 92 and passing through the cooling mandrel 30. A method for improving the crystallinity of the surface portion of 20 ′ can be employed.

  That is, with the movement of the polylactic acid resin foam sheet 20 ′, the heating roll 40 having an outer peripheral surface in contact with the polylactic acid resin foam sheet 20 ′ is rotated to provide the polylactic acid resin foam sheet 20 ′. Can be employed from the both sides to improve the crystallinity of the surface layer.

  In particular, as shown in FIG. 1, in the method of contacting the heating roll, the heating temperature of the polylactic acid resin foam sheet can be accurately controlled because the heating roll is brought into direct contact with the polylactic acid resin foam sheet. And the temperature increase rate of a polylactic acid-type resin foam sheet can be made faster compared with radiation heating etc.

In this heat treatment step, the cell membrane is partially broken by causing molecular rearrangement in the polylactic acid resin forming the cell membrane of the polylactic acid resin foam sheet, thereby increasing the open cell ratio.
Therefore, it can be said that it is advantageous to perform the heat treatment step using a plurality of heating rolls in this respect as well.

That is, in the present embodiment, the belt-shaped polylactic acid resin foam sheet 20 ′ that has been divided into two parts up and down after passing through the cooling mandrel is provided with four heating elements arranged in order along the moving path conveyed in the longitudinal direction. The rolls are heated by being alternately wound so that the contact surfaces are opposite to each other. For example, the polylactic acid resin foam sheet is wound on the first heating roll closest to the cooling mandrel. When passing, the first heating of heating one side of the polylactic acid resin foam sheet with the first heating roll is performed, and the polylactic acid resin foam sheet after passing through the first heating roll is Then, the second heating roll is wound around the second heating roll so that the one surface side becomes the outer side, but the second heating roll is opposite to the surface heated by the first heating roll. Other The surface side is heated, and the second heating subsequent to the first heating is performed.
At this time, in the second heating roll, the side heated by the first heating roll becomes the outside, and the tension is easily applied as compared with the inside contacting the second heating roll.
Therefore, when the surface where crystallization progressed due to the rearrangement of molecules in the first heating roll is wound around the second heating roll, it is possible to make it easy to damage the bubble film by receiving tension. .

In this heat treatment step, it is possible to adjust the open cell ratio by the heating temperature, the heating time, or the method of applying the tension as described above. There is a possibility that the obtained sheet molded product will have insufficient strength, and if the improvement of the excessive open cell ratio is suppressed, it may result in the foaming agent remaining in the sheet molded product.
Therefore, in order to more reliably obtain a sheet molded product with less foaming agent remaining and excellent strength, the heat treatment step is performed with the open cell ratio of the polylactic acid resin foam sheet for thermoforming obtained through the heat treatment step. It is preferable to implement so that it may become 25 to 60%.

In addition, this heat treatment step is preferably performed so that the crystallinity of the polylactic acid resin foam sheet for thermoforming obtained through the heat treatment step is 40% or more, and the polylactic acid resin foam sheet for thermoforming is used. It is preferable to carry out so that the amount of heat generated by crystallization is 1 mJ / mg or less when DSC is measured.
Especially, it is preferable to implement a heat treatment process to such an extent that the crystallization calorific value is not substantially observed when the polylactic acid-type resin foam sheet for thermoforming is measured by DSC.

  In order to bring the polylactic acid resin foam sheet for thermoforming into the state as described above, the temperature of the heating roll is usually set to 120 ° C. to 160 ° C., and the heating roll and the polylactic acid resin foam sheet are used. The contact time may be adjusted to about 35 seconds to 110 seconds.

The polylactic acid-based resin foam sheet for thermoforming according to the present embodiment can be effectively used for the production of a sheet molded product by performing thermoforming such as match mold molding and plug-assist vacuum molding. It can be effectively used in a method for producing a small number of sheet molded articles.
When the foaming agent is a hydrocarbon-based foaming agent, the amount of the hydrocarbon-based foaming agent contained in the sheet molded product after the thermoforming is suppressed to 0.3% by mass or less. preferable.
In addition, when the sheet forming step is carried out using a foaming agent that causes a change in the odor or significant characteristic of the sheet molded product over time even when it is not a hydrocarbon-based foaming agent, It is preferable that the amount of the foaming agent remaining in the sheet molded product is suppressed to 0.3% by mass or less in the same manner as the system foaming agent.

  In addition, the sheet molded product obtained in this way is excellent in surface strength and impact resistance because the surface layer portion is hard and exhibits excellent strength by the heat treatment step, and is a lunch box, cup noodle container, fruit container, vegetable container It is suitable for food packaging containers such as, precision instruments, and buffer packaging containers for electrical products.

  In addition, the polylactic acid-type resin foam sheet obtained by the manufacturing method of this embodiment does not limit the use to the above uses, but can be utilized for various uses.

  Although not described in detail here, the conventionally known technical matters relating to the forming material and manufacturing method of the polylactic acid-based resin foamed sheet are the polylactic acid-based resin foamed sheets of the present invention within a range where the effects of the present invention are not significantly impaired. And can be appropriately employed in the manufacturing method thereof.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

Example 1
(Preparation of polylactic acid foam sheet for thermoforming)
First, a tandem type extruder in which a second extruder (L / D: 34, caliber: 65 mm) is connected to the tip of a first extruder (L / D: 29, caliber: 50 mm) via a connecting pipe. Prepared.
Crystalline polylactic acid resin (trade name “TERRAMAC HV6250H” manufactured by Unitika Ltd., melting point (mp): 166.2 ° C., D-form ratio: 1.4 mol%, L-form ratio: 98.6 mol%) and bubbles A blended resin (trade name “Kinoplus BLBD-A1107” manufactured by Sumika Color Co., Ltd.) blended with polytetrafluoroethylene (PTFE) as a regulator is added to a PTFE blended resin 1.0 per 100 parts by mass of the crystalline polylactic acid resin. The mixture was mixed so as to be part by mass and supplied to the first extruder of this tandem type extruder.
Next, butane is press-fitted from the middle of the first extruder as a foaming agent, the molten resin composition in a molten state and butane are uniformly kneaded, and the molten resin composition containing the foaming agent is put into the second extruder. While continuously supplying and melt-kneading, it was cooled to a resin temperature suitable for foaming.
Thereafter, the molten resin composition was extruded and foamed from a circular mold having a slit diameter of 70 mm attached to the tip of the second extruder under conditions of a discharge rate of 30 kg / h and a resin temperature of 167 ° C., and extruded and foamed from the mold slit. A cylindrical polylactic acid resin foam sheet is placed on a cooled mandrel, and the outer surface is blown by air from an air ring, cooled, cut by a cutter, and flat sheet polylactic acid resin foam The sheet | seat was produced and the sheet forming process in the manufacturing method of the polylactic acid-type resin foam sheet for thermoforming of Example 1 was implemented.
Next, as shown in FIG. 1, the polylactic acid-based foamed sheet obtained by the extrusion foaming is applied to four dielectric heating-type heating rolls (roll diameter: 300 mm, roll temperature: 140 ° C.) arranged in a staggered manner in the vertical direction. Polylactic acid for thermoforming by wrapping and passing at a roll speed of 3 m / min (contact time between sheet and heating roll: 36 seconds in total) and performing a heat treatment step of alternately heating both sides of the polylactic acid-based foamed sheet A system foamed sheet was prepared.

(Production of sheet molded product)
A one-side vacuum type match mold with a tray container shape (outside of container opening: 115 mm × 185 mm, outside of bottom: 70 mm × 115 mm, outside of container depth: 30 mm), mold atmosphere temperature 165 ° C., male The mold temperature was set to 165 ° C. and the female mold temperature was set to 50 ° C., and the polylactic acid-based foamed sheet for thermoforming was preheated in the mold for 15 seconds and then press-molded to produce a sheet molded product (tray container).

(Example 2)
A polylactic acid foam sheet for thermoforming was prepared in the same manner as in Example 1 except that the resin temperature during extrusion was changed to 169 ° C. instead of 167 ° C., and a tray container was similarly prepared.

(Comparative Example 1)
A polylactic acid-based foamed sheet for thermoforming was prepared in the same manner as in Example 2 except that a dielectric heating type heat roll was not used and the heat treatment step was not performed, and a tray container was similarly prepared.

(Evaluation)
Polylactic acid-based foam sheet (hereinafter also referred to as “raw fabric”) collected without performing the heat treatment step using the heating roll, and polylactic acid-based foam sheet for thermoforming that has undergone the heat treatment step (hereinafter also referred to as “heat-treated product”). And, an evaluation sample of the remaining amount of foaming agent was collected from a tray container (hereinafter also referred to as “molded product”).
In addition, with respect to the raw fabric and the heat-treated product, two evaluation samples were collected at positions 200 mm inside from both side edges of the sheet, respectively, and with respect to the molded product, one each from the bottom and side walls (total 2). Samples) were collected.

(Headspace method)
Regarding the evaluation sample, the amounts of butane and pentane were measured by the headspace method in the following manner.

(Measuring method)
Put 10-30 mg of sample into a 20 mL vial, weigh it, seal it, set it on a gas chromatograph with an autosampler, heat it at 190 ° C. for 20 min, and then use Perkins Elmer gas chromatograph “Claras500GC” (detector: FID). Quantitative analysis was carried out by the MHE (Multiple Headspace Extraction) method.
The measurement conditions in the headspace sampler were a needle temperature of 190 ° C., a sample introduction time of 0.08 minutes, and a transfer line temperature of 200 ° C. The measurement conditions in the gas chromatograph were as follows. DB-1 (0.25 mmφ × 60 m, film thickness 1 μm, column temperature: 6 minutes at 50 ° C., temperature rise to 250 ° C. at 40 ° C./min, 1 at 250 ° C. 5 minutes), carrier gas helium (introduction conditions: 10 psi at 18 psi, increased to 24 psi at 0.5 psi / min), inlet temperature 200 ° C., detector temperature 310 ° C., range = 20, Att = 1 It was.

Table 1 below also shows the results of evaluating the open cell ratio and crystallinity of the raw fabric, heat-treated product, and molded product.
In addition, since the pentane which should not be observed originally was also observed slightly, it quantified together.
This pentane appears to be mixed as an impurity.

  As described above, according to the present invention, it is understood that the open cell ratio can be adjusted by providing a relatively simple process called a heat treatment process, and a sheet molded product with a small amount of remaining foaming agent can be produced.

1: Circular die, 20: Polylactic acid resin foam sheet, 40: Heating roll, 70: Tandem type extruder

Claims (5)

A thermoforming polylactic acid resin foam sheet for producing a polylactic acid resin foam sheet for thermoforming by carrying out a sheeting process for producing a polylactic acid resin foam sheet by extruding and foaming a polylactic acid resin together with a foaming agent A manufacturing method comprising:
The polylactic acid-based resin foam sheet obtained by the sheet forming step the polylactic acid resin is heated above the crystallization onset temperature further implement heat treatment process to improve the open cell ratio of the polylactic acid-based resin foam sheet ,
In the heat treatment step, the heating is performed until the open cell ratio of the polylactic acid-based resin foam sheet is 25% or more and 60% or less and the heat of crystallization of the polylactic acid-based resin foam sheet is 1 mJ / mg or less. The manufacturing method of the polylactic acid-type resin foam sheet for thermoforming characterized by these.   2. The polylactic acid resin foam sheet for thermoforming according to claim 1, wherein the heat treatment step is performed by bringing a heating roll heated to a temperature higher than the crystallization start temperature into contact with the surface of the polylactic acid resin foam sheet. Production method.   Two or more heating rolls are arranged in order on a path for conveying the belt-shaped polylactic acid resin foam sheet in the longitudinal direction, and the polylactic acid resin foam sheet is wound around the first heating roll of the heating rolls. When passing, the one surface side of the polylactic acid-based resin foamed sheet is heated with the first heating roll, and the one surface side of the polylactic acid-based resin foamed sheet after passing through the first heating roll is outside. The second heating roll is passed through the second heating roll, and the second heating roll heats the other surface side opposite to the surface heated by the first heating roll, and The manufacturing method of the polylactic acid-type resin foam sheet for thermoforming of Claim 2 which implements a heat treatment process. A sheet molded product production method for producing a sheet molded product by thermoforming a polylactic acid resin foam sheet for thermoforming produced by carrying out a sheet forming step of extruding and foaming a polylactic acid resin together with a foaming agent,
As the polylactic acid resin foam sheet for thermoforming, the polylactic acid resin foam sheet obtained in the sheeting step is heated to a temperature higher than the crystallization start temperature of the polylactic acid resin to obtain the polylactic acid resin foam sheet. Using the polylactic acid resin foam sheet for thermoforming obtained by further performing a heat treatment step for improving the open cell ratio, in the heat treatment step, the open cell ratio of the polylactic acid resin foam sheet is 25% or more and 60% or less. next, and, sheet molded article production method heat of crystallization of the polylactic acid-based resin foam sheet is characterized that you implement the heating until the following 1 mJ / mg.   The sheet molded product manufacturing method according to claim 4, wherein the foaming agent is a hydrocarbon-based foaming agent, and a sheet molded product having a residual amount of the hydrocarbon-based foaming agent of 0.3% by mass or less is manufactured.

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