JP2022083435A - Foamed sheet, product, and method for producing foamed sheet - Google Patents

Abstract

To provide a foamed sheet that has a high cushioning property and high sheet strength.SOLUTION: A foamed sheet according to the present invention includes: a polylactic acid; and a filler, wherein the foamed sheet has a compressive stress of 0.2 Mpa or less when the cushioning coefficient of the foamed sheet is 10 or less, and the foamed sheet has a puncture strength of 2 N or more when the sheet thickness of the foamed sheet is 2 mm.SELECTED DRAWING: None

Description

The present invention relates to a foamed sheet, a product, and a method for manufacturing a foamed sheet.

Foamed sheets are lightweight, have excellent cushioning properties, and can be easily molded into various shapes, and are therefore widely used as raw materials for products (resin molded products) such as bags and containers. As the material of the foam sheet, a thermoplastic resin such as a polystyrene resin, a polyolefin resin, or a polyester resin is used.

In recent years, due to increasing demand for environmental consideration, the use of biodegradable polymers that are naturally decomposed among polyester resins and the like has been studied as a material for foam sheets. Among them, polylactic acid is a plant-derived biodegradable polymer, has properties similar to polystyrene-based resins conventionally used for foam sheets, and is relatively higher than other biodegradable polymers. Since it has a melting point, toughness, transparency, chemical resistance, and the like, its use as a material for foamed sheets is being studied.

As a foamed sheet using polylactic acid, for example, a biodegradable resin film made of polylactic acid resin is laminated on one or both surfaces of a foamed base sheet made of a polystyrene resin foamed sheet, and the puncture strength is 7. A biodegradable resin laminated foam sheet having a concentration of 0 N or more is disclosed (see, for example, Patent Document 1).

One aspect of the present invention is to provide a foamed sheet capable of having high cushioning properties and sheet strength.

One aspect of the foamed sheet according to the present invention contains polylactic acid and a filler, has a compressive stress of 0.2 MPa or less when the buffer coefficient is 10 or less, and has a puncture strength when the sheet thickness is 2 mm. It is 2N or more.

One aspect of the present invention can provide a foamed sheet capable of having high cushioning properties and sheet strength.

It is a phase diagram which shows the state of a substance with respect to temperature and pressure. It is a phase diagram for defining the range of a compressible fluid. It is a schematic diagram which shows an example of the continuous kneading apparatus used for manufacturing a polylactic acid-based composition. It is a schematic diagram which shows an example of the continuous foam sheet making apparatus used for manufacturing the foam sheet which concerns on one Embodiment.

Hereinafter, embodiments of the present invention will be described in detail. The embodiment is not limited to the following description, and can be appropriately changed without departing from the gist of the present invention. Further, in the present specification, "-" indicating a numerical range means that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value unless otherwise specified.

<Foam sheet>
The foamed sheet according to one embodiment is a polylactic acid foam produced by foaming a composition containing polylactic acid (polylactic acid-based composition), and the compressive stress when the buffer coefficient is 10 or less is 0.2 Mpa. Below, the puncture strength when the sheet thickness is 2 mm is 2N or more.

The compressive stress is determined according to the method for measuring compressive stress-strain characteristics described in JIS K 6400-2: 2012 and ISO3386-1. As described above, the buffer coefficient can be determined in accordance with JIS Z 0235: 2002 and ISO4651. The cushioning coefficient represents the ability of the foamed sheet according to one embodiment to absorb impact energy, and is a value obtained by dividing the compressive stress obtained by the compression test by the compressive energy per unit volume (buffer coefficient = compressive stress / unit). (Compression energy per volume).

For the compressive stress, the average value of the buffering coefficients obtained by measuring a plurality of points (for example, three places) of the foamed sheet according to the embodiment and dividing each compressive stress by the compressive energy is related to the embodiment. It may be used as a cushioning coefficient of the foam sheet.

When the compressive stress exceeds 0.02 MPa and is 0.05 MPa or less (compressive stress A), when it exceeds 0.05 MPa and is 0.2 MPa or less (compressive stress B), and when it exceeds 0.2 MPa and is 0.3 MPa or less. (Compressive stress C) may be measured, and the buffer coefficient in the case of compressive stress A, compressive stress B, or compressive stress C may be measured. In any of the compressive stress A, the compressive stress B, and the compressive stress C, the lower the buffer coefficient, the more excellent the cushioning property is exhibited.

Specifically, the compressive stress is measured as follows.
That is, as the compressive stress measuring device, a calibrated load cell of Shimadzu's universal testing machines AG-50X, AGS-5kNX, and 5kN is used.
Punch or cut out a circle with a diameter of 50 mm evenly from the roll or sheet. If the sheet is thin, it will be 25 mm to 35 mm when multiple sheets are stacked (when the sample is sandwiched between the pressure plate and the support plate fixed to the universal tester and a force of 2.9 N to 3.0 N is applied). Punch or cut out the required number of sheets. The sheet is sandwiched between the pressure plate and the support plate, and pressure is applied at a speed of (100 ± 20) mm / min to (40 ± 1)% of the thickness of the test piece. If the stress does not reach 0.3 Mpa, the amount of compression may be changed to 70% of the thickness.
Further, the buffer coefficient is obtained based on the measured value of the first compression at that time in accordance with JIS Z 0235: 2002 and ISO4651. The above is repeated 3 times, and the buffer coefficient is obtained based on the average value of the 3 times.

Compression set is determined according to JIS K 6767: 1999 or ISO1856. When the bulk density of the foamed sheet is 0.025 g / cm ³ to 0.250 g / cm ³ , it is preferably 15% or less, more preferably 12.5% or less. If the compression set is 15% or less, the cushioning performance can be maintained even if the foamed sheet is used repeatedly.

Specifically, the compression set is measured as follows.
That is, the test pieces are rectangular parallelepipeds having parallel upper and lower surfaces, 50 mm square and a thickness of about 25 mm, and when the samples are thin, they are stacked to have a thickness of about 25 mm. The initial thickness is measured using a caliper. The number of test pieces is three. It consists of two parallel flat plates with a smooth surface and sufficient thickness that does not bend even when subjected to force, and four or more bolts and nuts, and has a structure that can be compressed by 25% from the initial thickness of the test piece. Place the test piece in the compression device. Then, the mixture is continuously left at (23 ± 2) ° C. and relative humidity (50 ± 5)% for 22 hours in a state of being compressed by 25% from the initial thickness. Then, the sample is removed from the compression device, left at (23 ± 2) ° C. and relative humidity (50 ± 5)% for 24 hours, and then the thickness of the same place where the initial thickness was measured is measured. The compression set is calculated from the following formula (I).
Compression set = (initial thickness-thickness after test) / initial thickness x 100 ... (I)

Examples of the physical property value representing the strength of the foamed sheet according to the embodiment include the tensile strength (tensile strength), the bending strength, the piercing strength, and the like of the foamed sheet. When using a foam sheet as a cushioning material, it is important that the contents do not tear and come out, and among these, high piercing strength is particularly required.

The tensile strength of the foamed sheet is determined in accordance with JIS K 6767: 1999. The tensile strength required in accordance with JIS K 6767: 1999 is preferably 0.3 MPa to 5.0 MPa when the bulk density of the foamed sheet is 0.025 g / cm ³ to 0.250 g / cm ³ . .. When the tensile strength of the foamed sheet is 0.3 MPa to 5.0 MPa, it is possible to reduce problems such as tearing when used as a cushioning material.

The bending strength (rigidity) of the foamed sheet is determined in accordance with JIS K 7171. The bending strength required in accordance with JIS K 7171 is preferably 50 MPa to 140 MPa, more preferably 60 MPa to 120 MPa. When the bending strength of the foamed sheet is 50 MPa to 140 MPa and the bulk density of the foamed sheet is 0.025 g / cm ³ to 0.250 g / cm ³ , the foamed sheet can have sufficient strength and is therefore foamed. Even if an external pressure is applied to the sheet, the foamed sheet is less likely to bend and can be prevented from being destroyed. Further, when the bulk density of the foamed sheet is 0.5 g / cm ³ to 0.8 g / cm ³ , the foamed sheet may contain fine foaming. Even in this case, if the bending strength of the foamed sheet is 50 MPa to 140 MPa, the foamed sheet can have sufficient strength.

The puncture strength is determined in accordance with JIS Z 1707 using a sample in which the sheet thickness of the foamed sheet according to one embodiment is 2 mm. When the sheet thickness of the foamed sheet according to one embodiment is thin, the puncture strength may be measured by stacking a plurality of foamed sheets according to one embodiment and setting the total sheet thickness to 2 mm. When the sheet thickness of the foamed sheet is thick, the piercing strength may be measured by cutting so that the sheet thickness of the foamed sheet is 2 mm.

Specifically, the piercing strength is measured as follows.
That is, the test piece is fixed with a jig, and a semi-circular needle having a diameter of 1.0 mm and a tip shape radius of 0.5 mm is used, for example, using a load cell of Shimadzu's universal testing machines AG-50X, AGS-5kNX and 50N. The needle is pierced at a test speed (50 ± 5) mm / min, and the maximum force (unit: N) until the needle penetrates is measured. The number of test pieces shall be 5 or more, and shall be collected so as to be averaged over the entire width of the product.

In the conventional Patent Document 1, the cushioning property of the biodegradable resin laminated foam sheet has not been studied. In order to use the foamed sheet containing polylactic acid as a cushioning material, the foamed sheet needs to have a high cushioning property. It is also important that the foamed sheet has high sheet strength so that damage such as tearing of the foamed sheet does not occur even if it is hit by a protrusion or the like.

As a result of diligent studies on foamed sheets containing polylactic acid, the inventor of the present application focused on the compressive stress and puncture strength of the foamed sheet. If the compressive stress of the foamed sheet containing polylactic acid is 0.2 Mpa or less when the buffer coefficient is 10 or less and the puncture strength is 2 N or more when the sheet thickness is 2 mm, the foaming of polylactic acid is fine and uniform. Can be in a good state. As a result, it has been found that the foamed sheet containing polylactic acid can contain fine and uniform foaming inside, so that the cushioning property and the sheet strength can be improved.

Generally, the thicker the foamed sheet is, the better the cushioning property is, but the foamed sheet according to one embodiment can exhibit excellent cushioning property and piercing strength even if the foamed sheet is thin. Therefore, the foamed sheet according to the embodiment has the same thickness, and can achieve both cushioning property and sheet strength.

The cushioning property of the foamed sheet according to the embodiment can be evaluated from the buffering coefficient of the foamed sheet according to the embodiment. The sheet strength of the foamed sheet according to one embodiment can be evaluated from the piercing strength.

In the biodegradability test of a biodegradable plastic obtained in accordance with JIS K 6953-2, the number of days required for 90% biodegradation is preferably 180 days or less, more preferably 120 days or less, still more preferably. 60 days or less.

The foamed sheet according to one embodiment contains polylactic acid and a filler, and further contains other components as necessary. Since the foamed sheet according to the embodiment is produced from the polylactic acid-based composition, it is also referred to as a polylactic acid-based composition foamed sheet. Each component contained in the foam sheet according to one embodiment will be described.

[Polylactic acid]
Polylactic acid is one of the aliphatic polyester resins, and is a polymer formed by polymerizing lactic acid by an ester bond. Since polylactic acid is biodegraded by microorganisms, it is used in relation to microplastics that remain in nature as a polymer material that is environmentally friendly and has a low environmental load.

The lactic acid constituting the polylactic acid may be either one or both of D-form (D-lactic acid) and L-form (L-lactic acid).

Examples of the polylactic acid include a homopolymer of D-lactic acid, a homopolymer of L-lactic acid, a copolymer of D-lactic acid and L-lactic acid (DL-lactic acid); D-lactide, L-lactide and DL. -Examples include a ring-opening polymer of one or more lactides selected from the group consisting of lactides. These may be used alone or in combination of two or more.

When a copolymer of D-lactic acid and L-lactic acid is used as the polylactic acid, the ratio of D-lactic acid and L-lactic acid is not particularly limited and can be appropriately selected depending on the intended purpose. In the D-lactic acid and L-lactic acid copolymers, the crystallinity tends to increase and the melting point and the glass transition point tend to increase as the smaller number of optical isomers decreases. Further, as the smaller number of optical isomers increases, the crystallinity tends to decrease and eventually becomes amorphous. Since the crystallinity is related to the heat resistance of the foamed sheet and the molding temperature of the foamed sheet, it may be used properly according to the intended use, and is not particularly limited.

The crystallinity means the crystallinity and the crystallization rate. High crystallinity means at least one of high crystallinity and high crystallization rate.

Polylactic acid may be appropriately synthesized or commercially available, but the weight average molecular weight required by gel permeation chromatography (GPC) of polylactic acid in order to improve the cushioning performance as a cushioning material is 100,000. The above is preferable, and more preferably 150,000 or more. On the other hand, the upper limit of the weight average molecular weight of polylactic acid is not particularly limited, but is preferably 350,000 or less from the viewpoint of suppressing the viscosity from becoming too high and facilitating production.

The weight average molecular weight (Mw) of the foamed sheet according to the present embodiment is not particularly limited and may be appropriately selected depending on the intended purpose, but can be measured using GPC. For example, the foamed sheet according to the present embodiment is placed in a tetrahydrofuran (THF) solution and heated to 65 ° C. to dissolve polylactic acid. Then, the solution is filtered through a 0.45 μm membrane filter to remove undissolved substances such as fillers contained in the THF solution. The weight average molecular weight (Mw) of the obtained foamed sheet is measured by using GPC using a calibration curve prepared from a polystyrene sample having a known molecular weight as a standard. The weight average molecular weight (Mw) of the foamed sheet may be measured, for example, based on the following measurement conditions. As the column, a column in which four TSKgel SuperHM-N (manufactured by Tosoh Corporation) are connected in series may be used.
(Measurement condition)
・ Equipment: HLC-8320 (manufactured by Tosoh)
-Column: TSKgel SuperHM-N (manufactured by Tosoh Corporation) x 4-Detector: RI
・ Measurement temperature: 40 ° C
-Mobile phase: Tetrahydrofuran-Flow rate: 0.6 mL / min

From the viewpoint of biodegradability and recyclability, the content of polylactic acid is preferably 98% by mass or more, more preferably 99% by mass or more, based on the total amount of organic substances in the foamed sheet according to the embodiment. When the content of polylactic acid is 98% by mass or more, even if polylactic acid is biodegraded, it is possible to suppress the remaining of other components that are not biodegradable.

The content of lactic acid contained in polylactic acid can be calculated from the ratio of materials forming polylactic acid. When the material ratio is unknown, for example, analysis using gas chromatography-mass spectrometry (GC-MS) can be performed, and the components can be specified by comparison using known polylactic acid as a standard sample. Specifically, by using a known polylactic acid as a standard sample and obtaining a calibration curve in advance, the ratio of polylactic acid in the foamed sheet according to one embodiment can be obtained. Further, if necessary, the area ratio of the spectrum by NMR measurement and other analysis methods can be combined and calculated. When GC-MS is used, the content ratio of polylactic acid can be measured, for example, under the following conditions.
(Measurement by GCMS)
-GCMS: QP2010 Auxiliary Equipment Frontier Lab Py3030D, manufactured by Shimadzu Corporation-Separation column: Frontier Lab Ultra ALLOY UA5-30M-0.25F
-Sample heating temperature: 300 ° C
-Column oven temperature: 50 ° C (holding for 1 minute) -heating rate 15 ° C / min-320 ° C (holding for 6 minutes)
-Ionization method: Electron Ionization (EI) method-Detection mass range: 25 to 700 (m / z)

[Filler]
The filler has a function of adjusting the size and amount of foam contained in the foamed sheet according to the embodiment, and can be used as a foaming nucleating agent. Since the foamed sheet according to the embodiment contains a filler, the foamed diameter in the foamed sheet can be made fine and uniform, so that both piercing strength and cushioning property can be achieved.

As the filler, an inorganic filler, an organic filler, or the like can be used. These may be used alone or in combination of two or more.

Since foaming occurs at the interface between the filler and polylactic acid, it is preferable to disperse the filler finely and uniformly.

The content of the filler is preferably 0.1% by mass to 5.0% by mass. When the content of the filler is 0.1% by mass or more, it is sufficient as an amount that functions as a core of foaming, and when the content of the filler is 5.0% by mass or less, sufficient impact resistance is exhibited. The characteristics of the foam sheet can be maintained. The content of the filler is more preferably 0.2% by mass to 4.0% by mass, and further preferably 0.3% by mass to 2.0% by mass.

Examples of the inorganic filler include talc, kaolin, calcium carbonate, layered silicate, zinc carbonate, wallastonite, silica, alumina, magnesium oxide, titanium oxide, calcium silicate, sodium aluminate, calcium aluminate, and aluminosilicate. Sodium, magnesium silicate, glass balloon, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fiber, metal whiskers, ceramic whiskers, potassium titanate, boron nitride, graphite, glass fiber, carbon fiber, etc. Be done.

Organic fillers include naturally occurring polymers such as starch, cellulose fine particles, wood flour, okara, fir shells, and bran, modified products thereof, sorbitol compounds, benzoic acid and metal salts of the compounds, and phosphoric acid ester metals. Examples thereof include salts and rosin compounds.

Among these, inorganic fillers are preferable because of their influence on the environment. Among the inorganic fillers, silica, titanium oxide, and layered silicate are more preferable because they can be dispersed at the nano level and bubbles can be made uniform.

[Other ingredients]
The other components are not particularly limited as long as they are usually contained in the foamed sheet and the amount is within the range that does not affect the biodegradation performance, and can be appropriately selected depending on the intended purpose. Examples thereof include aliphatic polyester resins other than polylactic acid, polymethylmethacrylate resins (PMMA) added for the purpose of controlling the foaming state, high molecular weight polymers such as polystyrene, cross-linking agents, and additives added for other purposes. , Not limited to that.

(Aliphatic polyester resin other than polylactic acid)
Examples of the aliphatic polyester resin other than polylactic acid include polyglycolic acid, poly (3-hydroxybutyrate), poly (3-hydroxybutyrate / 3-hydroxyhexanoate), and poly (3-hydroxybutyrate /. 3-Hydroxyvariate), polycaprolactone, polybutylene succinate, poly (butylene succinate adipate) and the like. These may be used alone or in combination of two or more.

(Crosslinking agent)
The cross-linking agent is not particularly limited as long as it is a compound having reactivity with the hydroxyl group and / or the carboxylic acid group of polylactic acid. For example, an epoxy-based cross-linking agent (cross-linking agent having an epoxy group) or an isocyanate-based cross-linking agent (cross-linking agent having an isocyanate group) is preferably used. As these cross-linking agents, for example, an epoxy functional (meth) acrylic-styrene cross-linking agent having two or more epoxy groups in the molecule or a polyisocyanate having two or more isocyanate groups in the molecule is preferable. Epoxy functional (meth) acrylic-styrene system having three or more epoxy groups in the molecule from the viewpoint that a branched structure can be introduced into polylactic acid, the melt strength can be efficiently improved, and the residual unreacted substance can be reduced. A cross-linking agent and a polyisocyanate having three or more isocyanate groups in the molecule are more preferable. When such a cross-linking agent is used, coalescence of bubbles and bubble rupture can be suppressed, and the foaming ratio can be improved.

Here, the epoxy functional (meth) acrylic-styrene-based cross-linking agent having two or more epoxy groups in the molecule was obtained by copolymerizing a (meth) acrylic monomer having an epoxy group and a styrene monomer. It is a polymer.

Examples of the (meth) acrylic monomer having an epoxy group include a monomer containing a 1,2-epoxy group such as glycidyl acrylate and glycidyl methacrylate. Examples of the styrene monomer include styrene and α-methylstyrene.

The epoxy functional (meth) acrylic-styrene cross-linking agent having two or more epoxy groups in the molecule may contain a (meth) acrylic monomer having no epoxy group in its copolymerization component. Examples of such (meth) acrylic monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate and the like.

Examples of the polyisocyanate having two or more isocyanate groups in the molecule include 1,6-hexamethylene diisocyanate, 3-isocyanatemethyl-3,5,5-trimethylcyclohexylisocyanate (isophoronediisocyanate), and 1,4-tetra. Methylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexyl-2,4-diisocyanate, methylcyclohexyl-2,6 -Diisocyanate, xylylene diisocyanate, 1,3-bis (isocyanate) methylcyclohexane, tetramethylxylylene diisocyanate, transcyclohexane-1,4-diisocyanate, lysine diisocyanate and other aliphatic diisocyanates, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, water Alicyclic polyisocyanates such as supplemented tolylene diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tetramethylxylylene diisocyanate, cyclohexanediisocyanate, 2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, diphenylmethane-4,4 Aromatic diisocyanates such as'-isocyanate, 1,5'-naphthendiisocyanate, trizine diisocyanate, diphenylmethylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 4,4'-dibenzyldiisocyanate, 1,3-phenylenediisocyanate, lysine ester triisocyanate , Triphenylmethane triisocyanate, 1,6,11-undecanetriisocyanate, 1,8-isocyanate-4,4-isocyanatemethyloctane, 1,3,6-hexamethylenetriisocyanate, bicycloheptane triisocyanate, trimethylolpropane And 2,4-toluylene diisocyanate and other adducts, trimethylol propane and triisocyanate compounds such as 1,6-hexamethylene diisocyanate and other diisocyanates, and polyhydric alcohols such as glycerin and pentaeristol. There are modified polyisocyanate compounds obtained by reacting with the aliphatic and aromatic diisocyanate compounds of the above and the above-mentioned triisocyanate compounds and the like. These may be used alone or in combination of two or more.

By containing a cross-linking agent, melt tension can be applied and the foaming ratio of the foamed sheet can be adjusted. A method of dispersing a filler such as a layered silicate at the nano level, a method of cross-linking a resin composition using a cross-linking agent or a cross-linking aid, a method of cross-linking a resin composition by an electron beam or the like, as a means for imparting melt tension. , There is a method of adding another resin composition having a high melt tension.

(Additive)
Examples of the additive include a heat stabilizer, an antioxidant, a plasticizer and the like. These may be used alone or in combination of two or more.

The content ratio of other components is preferably 2% by mass or less, more preferably 1% by mass or less, based on the total amount of organic substances in the foamed sheet, from the viewpoint of recyclability.

It is preferable that the foamed sheet according to the embodiment substantially does not contain an organic compound having a boiling point of −20 ° C. or higher and lower than 150 ° C. "Substantially not included" indicates that the detected value is not less than the lower limit of the analyzer even after analysis, or is not more than the detected value when the same operation is performed with the raw material polylactic acid. Substantially not contained means that the content of the organic compound is substantially 0% by mass, and does not mean that the content is 0% by mass. That is, the organic compound may be contained as an unavoidable impurity, for example, in an amount of 0.1% by mass or less. As an organic compound having a boiling point of −20 ° C. or higher and lower than 150 ° C., there is a volatile component. When the volatile component is, for example, an organic solvent or a foaming agent such as butane, if the volatile component is contained in the foam sheet, it affects the dimensional stability of the foam sheet and also affects the environment. In the foamed sheet according to one embodiment, a foaming agent other than an organic compound such as CO ₂ can be used, and the content of volatile components can be substantially 0% by mass, so that the foaming sheet can be safely handled without generating odor or the like. ..

<Physical characteristics of foam sheet>
As the physical properties of the foamed sheet according to one embodiment, the bulk density, the foaming ratio, the average foaming diameter, the sheet thickness and the amount of residual volatile components will be described.

(Bulk density)
The bulk density of the foamed sheet according to one embodiment is preferably 0.025 g / cm ³ to 0.250 g / cm ³ , more preferably 0.031 g / cm ³ to 0.125 g / cm ³ , and more preferably 0.036 g / cm. ³ to 0.083 g / cm ³ is more preferable. As long as the bulk density is within the above-mentioned preferable range, the foamed sheet according to the embodiment can have an excellent balance between sheet strength and cushioning property.

Bulk density refers to the density of the internal volume when a container is filled with a foam sheet. The bulk density measuring method is not particularly limited, and any bulk density measuring method can be used as appropriate. For example, the bulk density can be measured by the following method. The external dimensions of the foamed sheet left for 24 hours or more in an environment of a temperature of 23 ° C. and a relative humidity of 50% are measured, and the bulk volume is obtained. Then, the weight of this foamed sheet is measured. The bulk density of the foam sheet is obtained by dividing the weight of the foam sheet by the bulk volume.

(Effervescence magnification)
The foaming ratio of the foamed sheet according to one embodiment is preferably 5 to 50 times, more preferably 10 to 40 times, still more preferably 15 to 35 times. When the foaming ratio is within the above-mentioned preferable range, the foamed sheet according to the embodiment can maintain the cushioning performance and the strength.

The foaming ratio of the foamed sheet according to the embodiment is obtained by dividing the density (true density ρ0) of the polylactic acid-based composition constituting the foamed sheet by the bulk density (ρ1) as shown in the following formula (1). By doing so, you can ask for it. The true density here is the density of polylactic acid as a raw material, and the literature value or the pellet of the raw material may be actually measured. The true density is about 1.25 g / cm ³ .
Foaming magnification = true density (ρ0) / bulk density (ρ1) ... (1)

(Average foam diameter)
The average foam diameter of the foamed sheet according to one embodiment is preferably 10 μm to 200 μm, more preferably 20 μm to 100 μm, and further preferably 30 μm to 80 μm, although it depends on the bulk density.

The size of the average foam diameter can be appropriately adjusted depending on the content of the filler, the dispersed state of foam, the melt tension of the foam sheet, and the like, but is not limited thereto. For example, when the bulk density is 0.025 g / cm ³ to 0.250 g / cm ³ , the average foam diameter is preferably 100 μm or less.

The method for measuring the average foam diameter is not particularly limited, and can be appropriately selected depending on the intended purpose. For example, a foam sheet is cross-sectioned using an ion milling device, the cross-section is photographed by SEM, and an image SEM photograph is acquired. The obtained cross-sectional SEM photograph (magnification is, for example, 3000 times) is obtained by using the software of Image-Pro Premier (manufactured by mediacy), and the gray component corresponding to foaming (void) and the white corresponding to the resin component are used. It binarizes with the ingredients. Next, the average particle diameter (ferred diameter) of the gray component corresponding to foaming within a predetermined range (for example, 35 μm × 20 μm) is determined. The average foam diameter can be calculated by calculating the average value of only the gray component (foam) having a ferret diameter of 0.5 μm or more.

(Sheet thickness)
The sheet thickness of the foamed sheet according to one embodiment is preferably 1.0 mm to 10.0 mm, more preferably 1.5 mm to 7.0 mm, still more preferably 2.0 mm to 5.0 mm. As long as the sheet thickness is within the above-mentioned preferable range, the foamed sheet according to one embodiment can be foamed finely and uniformly, so that the foamed sheet according to one embodiment can be easily molded and has sufficient cushioning property. be able to.

The sheet thickness may be an average thickness. The average thickness may be the average value of the measured thicknesses obtained by measuring the thickness of the foamed sheet at a plurality of points in the cross section of the foamed sheet.

The foamed sheet according to the embodiment has a compressive stress of 0.2 Mpa or less, preferably 0.02 Mpa to 0.1 Mpa, and more preferably 0.02 Mpa to 0.05 Mpa when the buffer coefficient is 10 or less. Is. When the compressive stress is 0.2 MPa or less, the cushioning property is excellent.

The foamed sheet according to one embodiment has a puncture strength of 2N or more, preferably 2.5N to 5N, and more preferably 3N to 5N when the sheet thickness is 2 mm. When the piercing strength is 2N or more, it is possible to suppress tearing or the like starting from a protrusion or the like when used as a cushioning material.

<Manufacturing method of foam sheet>
The method for producing a foamed sheet according to an embodiment includes a kneading step and a foaming step, and further includes other steps as necessary. In the method for producing a foamed sheet according to an embodiment, the kneading step and the foaming step may be performed at the same time or separately.

[Kneading process]
In the kneading step, polylactic acid and the filler are kneaded at a temperature lower than the melting point of polylactic acid in the presence of a compressible fluid. In the kneading step, it is preferable to add a foaming agent in addition to polylactic acid and the filler in order to promote foaming more efficiently. A mixture containing polylactic acid, a filler and a foaming agent and before foaming is also referred to as a polylactic acid-based composition (master batch).

(Effervescent agent)
As the foaming agent, hydrocarbons such as lower alkanes such as propane, normal butane, isopentane, normal pentane, isopentane, and hexane, ethers such as dimethyl ether, and methyl chloride, are used in that a foamed sheet having a high foaming ratio can be easily obtained. Examples thereof include halogenated hydrocarbons such as ethyl chloride, and physical foaming agents such as compressible fluids (also referred to as compressible gases) such as carbon dioxide and nitrogen. Among these, it is preferable to use a compressible fluid such as carbon dioxide or nitrogen from the viewpoint of using a foaming agent that has no odor, can be handled safely, and has a low environmental load. As a result, the foamed sheet according to the embodiment does not substantially contain an organic compound having a boiling point of −20 ° C. or higher and lower than 150 ° C. That is, the content of the organic compound having a boiling point of −20 ° C. or higher and lower than 150 ° C. is substantially 0% by mass.

Since the aliphatic polyester resin such as polylactic acid has a property that the melt viscosity rapidly decreases after the melting point, the filler tends to aggregate when the filler is kneaded together with polylactic acid. When the filler is small, the agglomeration of the filler is particularly noticeable. Therefore, in the present embodiment, it is preferable to knead the polylactic acid and the filler with a compressible fluid. This makes it possible to uniformly disperse the filler in polylactic acid.

It is preferable that the compressible fluid is the same as the foaming agent. When the compressible fluid is the same as the foaming agent, the filler can be kneaded and foamed in a series of processes, so that the environmental load can be reduced.

The reason why it is preferable to use a compressible fluid for kneading the filler and polylactic acid will be explained. In general, a resin such as an aliphatic polyester resin is plasticized by a compressible fluid, and the melt viscosity of the resin tends to decrease (see "Latest Applied Technology of Supercritical Fluid", NTS). At first glance, the decrease in melt viscosity and the improvement in kneadability seem to be inconsistent. In fact, by applying pressure without using a compressible fluid in the kneading of a general filler, the free volume of the resin can be reduced and the interaction between the resins can be increased (viscosity increase). However, the resin becomes difficult to plasticize ("k. Yang. R. Ozisk R. Polymer, 47.2849 (2006)".
reference).

It has been known that a compressible liquid has a property of plasticizing (softening) a resin, and that the resin becomes like a liquid when the temperature of the compressible liquid is raised. When the filler is dispersed in the resin in such a state, the filler is dispersed in the liquid, and the filler aggregates in the liquid. Therefore, a resin composition in which the filler is highly dispersed cannot be obtained. That is, it has been considered difficult to use a compressible liquid for kneading the resin and the filler because the resin does not have a viscosity suitable for kneading in the presence of the compressible fluid.

The inventors of the present application investigated whether a compressible fluid could be used for kneading polylactic acid and a filler. As a result, it was found that, in the presence of a compressible fluid, the polylactic acid has a viscosity suitable for kneading at a temperature lower than the melting point of the polylactic acid, and the filler can be kneaded with the polylactic acid. In particular, polylactic acid whose melt viscosity drops sharply above the melting point has been kneaded only in a state of low melt viscosity. However, in the present embodiment, the filler can be kneaded even when polylactic acid has a high viscosity, and the compressible fluid can be used as it is as a foaming agent.

(Compressible fluid)
Examples of the substance that can be used in the state of a compressible fluid include carbon monoxide, carbon dioxide, dinitrogen monoxide, nitrogen, methane, ethane, propane, 2,3-dimethylbutane, ethylene, dimethyl ether and the like. .. Among these, carbon dioxide is preferable because it has a critical pressure of about 7.4 MPa and a critical temperature of about 31 ° C., can easily create a supercritical state, is nonflammable, and is easy to handle. These compressible fluids may be used alone or in combination of two or more.

Here, the compressible fluid used for producing the polylactic acid resin composition will be described with reference to FIGS. 1 and 2. FIG. 1 is a phase diagram (state diagram) showing the state of a substance with respect to temperature and pressure. FIG. 2 is a phase diagram (state diagram) for defining the range of the compressible fluid. The compressible fluid in the present embodiment is a state when the substance is present in any of the regions (1), (2) and (3) shown in FIG. 2 in the phase diagram shown in FIG. Means.

In such a region, it is known that the substance has a very high density and behaves differently from that at normal temperature and pressure. When the substance is present in the region (1), it becomes a supercritical fluid. The supercritical fluid is a fluid that exists as a non-condensable high-density fluid in a temperature and pressure region exceeding the limit (critical point) at which a gas and a liquid can coexist, and does not condense even when compressed. When the substance is present in the region (2), it becomes a liquid, but represents a liquefied gas obtained by compressing the substance which is in a gaseous state at normal temperature (25 ° C.) and normal pressure (1 atm). When the substance is present in the region (3), it is in a gaseous state, but represents a high-pressure gas whose pressure is ½ (1 / 2Pc) or more of the critical pressure (Pc).

Since the solubility of the compressible fluid changes depending on the type of resin, the combination of the compressible fluid, the temperature and the pressure, it is necessary to appropriately adjust the supply amount of the compressible fluid. For example, when the compressible fluid is carbon dioxide, in the case of a combination of polylactic acid and carbon dioxide, the supply amount of carbon dioxide is preferably 2% by mass to 30% by mass. If the amount of carbon dioxide supplied is 2% by mass or more, the problem that the effect of plasticization is limited can be suppressed. When the supply amount of carbon dioxide is 30% by mass or less, carbon dioxide and polylactic acid are phase-separated, and the foamed sheet can have a uniform thickness.

(Kneading device)
As the kneading device used for producing the polylactic acid-based composition, a continuous process or a batch process can be adopted, but in consideration of the device efficiency, product characteristics, quality, etc., It is preferable to select the reaction process as appropriate.

As a kneading device, a single-screw extruder, a twin-screw extruder, a kneader, a non-screw cage type stirring tank, a Vivorac manufactured by Sumitomo Heavy Industries, Ltd., and an N- made by Mitsubishi Heavy Industries, Ltd. SCR, Hitachi, Ltd. glasses wing, lattice wing or Kenix type, Zulzer type SMLX type static mixer equipped tube type polymerization tank and the like can be used. From the point of view of color tone, a self-cleaning type polymerization apparatus such as a finisher, N-SCR, and a biaxial extruded ruder can be mentioned. Among these, the finisher and N-SCR are preferable from the viewpoints of production efficiency, resin color tone, stability and heat resistance.

As the kneading device, a continuous kneading device as shown in FIG. 3 can be used. FIG. 3 is a schematic view showing an example of a continuous kneading device used for producing a polylactic acid-based composition. As shown in FIG. 3, the continuous kneading device 10 includes an extruder 11, quantitative feeders 12A and 12B, and a gas introduction unit 13.

The extruder 11 has a raw material mixing / melting area a, a compressible fluid supply area b, a kneading area c, a compressible fluid removal area d, and a molding processing area e inside the extruder 11. As the extruder 11, for example, a twin-screw extruder can be used. The screw diameter, the ratio L / D of the shaft diameter L to the screw shaft length D, and the like of the extruder 11 can be appropriately set to any size.

In the quantitative feeder 12A, polylactic acid, which is a raw material for the foamed sheet, is charged into the raw material mixing / melting area a. The quantitative feeder 12B supplies a filler as a raw material for the foamed sheet to the raw material mixing / melting area a.

The gas introduction unit 13 supplies the compressible fluid from the gas tank 131 to the compressible fluid supply area b by the measuring pump 132.

The continuous kneading device 10 kneads polylactic acid and the filler together with the compressible fluid in the raw material mixing and melting area a, the compressible fluid supply area b, the kneading area c, and the compressible fluid removal area d in the extruder 11. This produces a polylactic acid-based composition. Next, in the molding processing area e, the polylactic acid-based composition is molded into pellets or the like.

(Raw material mixing and melting area)
In the raw material mixing and melting area a, polylactic acid and filler are mixed and the temperature is raised. The heating temperature is set to be equal to or higher than the melting temperature of polylactic acid, and the polylactic acid is melted to obtain a polylactic acid-based composition containing a filler in the melted polylactic acid. As a result, the compressible fluid supplied into the extruder 11 and the polylactic acid-based composition can be uniformly mixed in the subsequent compressible fluid supply area b.

(Compressible fluid supply area)
In the compressible fluid supply area b, the compressible fluid is supplied into the extruder 11 to plasticize the molten polylactic acid contained in the polylactic acid-based composition.

(Kneading area)
In the kneading area c, the temperature of the kneading area c is set so as to have a viscosity suitable for kneading the filler. The set temperature varies depending on the specifications of the continuous kneading device 10, the type, structure, molecular weight, etc. of polylactic acid, and is therefore appropriately adjusted. For example, when the weight average molecular weight Mw of polylactic acid is about 200,000, kneading is generally performed at + 10 ° C to + 20 ° C higher than the melting point of polylactic acid. On the other hand, in the present embodiment, since the polylactic acid-based composition has a relatively high viscosity even at a temperature lower than the melting point of polylactic acid, the polylactic acid-based composition can be kneaded at a temperature lower than the melting point of polylactic acid.

The temperature lower than the melting point of polylactic acid is preferably −20 ° C. to −80 ° C., more preferably −30 ° C. to −60 ° C., which is lower than the melting point of polylactic acid.

Since the temperature of the kneading area c can be lower than the temperature lower than the melting point of polylactic acid, for example, when the temperatures of the raw material mixing / melting area a, the compressible fluid supply area b and the compressible fluid removal area d are 190 ° C. The set temperature of the kneading area c can be set to 150 ° C.

The set temperature may be set with reference to the current value of the stirring power of the continuous kneading device 10 or the like.

(Compressible fluid removal area)
In the compressible fluid removal area d, the pressure valve 14 provided in the extruder 11 is opened to discharge the compressible fluid in the extruder 11 to the outside.

(Molding area)
In the molding processing area e, the polylactic acid-based composition is molded into a polylactic acid-based composition having an appropriately arbitrary shape such as pellets.

The pressure in each area in the extruder 11 can be appropriately set, and for example, the pressure from the compressible fluid supply area b to the compressible fluid removal area d can be set to 7 Mpa.

In the present embodiment, the polylactic acid-based composition molded into an arbitrary shape may be mixed again with polylactic acid and kneaded to form a polylactic acid-based composition. At this time, using the same extruder as the extruder 11, the raw material mixing / melting area a, the compressible fluid supply area b, the kneading area c, the compressible fluid removal area d, and the molding processing area e may be performed in the same manner. good.

[Foaming process]
The foaming step removes the compressible fluid contained in the polylactic acid-based composition to foam the polylactic acid-based composition.

The compressible fluid can be removed by reducing the pressure in the extruder 11 of the continuous kneading device 10.

As the temperature in the foaming step, it is preferable to heat the temperature to a temperature equal to or higher than the melting point of polylactic acid.

In the foaming step, the compressible fluid dissolved in the polylactic acid-based composition vaporizes at the interface with the filler and precipitates in response to operations such as depressurization and heating to change the solubility of the compressible fluid, resulting in foaming. Get up. Since foaming starts from the filler, the polylactic acid foam having uniform and fine foaming can be produced only when the filler is uniformly dispersed in the polylactic acid.

[Other processes]
The other steps are not particularly limited as long as they are steps performed in the production of a normal foamed sheet, and can be appropriately selected depending on the intended purpose. For example, a molding step for processing a polylactic acid foam into a foamed sheet. , A printing process for printing or the like on the surface of a foam sheet.

The molding method is not particularly limited, and a generally used thermoplastic resin molding method can be used. Examples of the molding method include a method of molding a polylactic acid foam into a sheet by using a mold such as vacuum forming, pneumatic forming, vacuum forming, press molding, or the like to obtain a foam sheet.

By molding the polylactic acid foam into a sheet by the molding step, the foamed sheet according to one embodiment can be obtained.

The printing step is not particularly limited as long as it is a method capable of printing or the like on the surface of the foam sheet according to the embodiment.

The foamed sheet according to one embodiment contains polylactic acid and a filler, has a compressive stress of 0.2 MPa or less when the buffer coefficient is 10 or less, and has a puncture strength of 2 N or more when the sheet thickness is 2 mm. As a result, foaming can be finely and uniformly formed in the foamed sheet. Since the viscosity of polylactic acid drops sharply when the temperature is close to the melting point, foam rupture, coalescence of foaming, etc. are likely to occur, and it is difficult to make the foaming finer and more uniform. Even if the foamed sheet according to the embodiment contains polylactic acid, the compressive stress having a buffering coefficient of 10 or less is 0.2 MPa or less, and the puncture strength when the sheet thickness is 2 mm is 2 N or more. And can include uniform foaming. Therefore, the foamed sheet according to the embodiment can enhance the cushioning property and the sheet strength.

The foamed sheet according to the embodiment can have a compressive stress of 0.05 Mpa or less. As a result, the foamed sheet according to the embodiment can enhance the cushioning property even when the compressive stress is 0.05 Mpa or less.

The foamed sheet according to one embodiment can have a piercing strength of 5 N or less. Thereby, the foamed sheet according to the embodiment can surely maintain the cushioning property.

The foamed sheet according to one embodiment can have a piercing strength of 3N or more. Thereby, the foamed sheet according to the embodiment can maintain the sheet strength more reliably.

The foamed sheet according to the embodiment can have a sheet thickness of 1 mm to 10 mm. Thereby, the foamed sheet according to the embodiment can further enhance the cushioning property and the sheet strength.

The foamed sheet according to one embodiment can have a foaming ratio of 5 to 50 times. Thereby, the foamed sheet according to the embodiment can further enhance the cushioning property.

The foamed sheet according to one embodiment can have a bulk density of 0.025 g / cm ³ to 0.250 g / cm ³ . Thereby, the foamed sheet according to the embodiment can have excellent sheet strength and cushioning property in a well-balanced manner.

The foamed sheet according to the embodiment can be substantially free of organic compounds having a boiling point of −20 ° C. or higher and lower than 150 ° C. Since the foamed sheet according to the embodiment can be foamed by using a compressible fluid such as CO ₂ or N ₂ as the foaming agent, the organic solvent used as the foaming agent as an organic compound having a boiling point of −20 ° C. or higher and lower than 150 ° C. The content of volatile components such as butane and butane can be reduced to substantially 0% by mass. Therefore, the foamed sheet according to the embodiment has excellent dimensional stability and can drastically reduce the impossibility to the environment.

The foamed sheet according to one embodiment can have a polylactic acid content of 98% by mass or more with respect to the total amount of organic substances in the foamed sheet. As a result, the foamed sheet according to the embodiment can be biodegraded with high efficiency when reused after use, and can be easily recycled.

The foamed sheet according to one embodiment can have a filler content of 0.1% by mass to 5.0% by mass. Thereby, the foamed sheet according to the embodiment can further surely enhance the cushioning property.

As described above, the foamed sheet according to the embodiment has high cushioning properties and sheet strength, and therefore can be suitably used as a packaging material, a cushioning material, or the like.

<Manufacturing>
The product according to one embodiment contains the foamed sheet according to one embodiment, and further contains other components as necessary. The other components are not particularly limited as long as they are used in ordinary resin products, and can be appropriately selected depending on the intended purpose.

Examples of the product (also referred to as “consumable material”) according to the embodiment include, as a daily item, a bag, a packaging container, a tray, tableware, cutlery, stationery, and other cushioning materials. The concept of this product is that as an intermediate for processing the product, not only the raw fabric made by rolling the sheet, the product as a single unit, but also the parts consisting of the product such as the handle of the tray. Also included are products with products such as trays with handles attached.

Examples of the bag include a plastic shopping bag, a shopping bag, and a garbage bag.

Examples of stationery include clear files, emblems, and the like.

Since the conventional foamed sheet has a large foam diameter and a large variation, there is a problem in the sheet physical properties such as the strength and flexibility of the sheet. Since the product according to one embodiment has excellent physical characteristics, it can be applied to applications other than the above-mentioned daily necessities. For example, it can be widely applied as an industrial material, a daily product, an agricultural product, a food product, a pharmaceutical product, a sheet for cosmetics, a packaging material, and the like.

Hereinafter, embodiments will be described in more detail with reference to Examples and Comparative Examples, but the embodiments are not limited to these Examples and Comparative Examples.

<Example 1>
[Making foam sheet]
Since the foamed sheet was carried out using the continuous foamed sheet kneading device 10 shown in FIG. 3 and the continuous foamed sheet forming device shown in FIG. 4, the foamed sheet will be described with reference to FIGS. 3 and 4.

(Making a masterbatch)
The polylactic acid-based composition was prepared using the continuous kneading device 10 shown in FIG. First, polylactic acid (Revode 110, manufactured by HISUN, melting point 160 ° C.) and titanium oxide (TTO-55 (C), manufactured by Ishihara Sangyo Co., Ltd., average particle diameter 0.004 μm) as a filler (foaming nucleating agent) are used. , The filler was supplied to the raw material mixing / melting area a so that the total flow rate of the filler was 10 kg / h. The flow rate of polylactic acid was 9.7 kg / h, and the flow rate of the filler was 0.3 kg / h. Next, carbon dioxide, which is a compressible fluid, was supplied to the compressible fluid supply area b at a flow rate of 0.99 kg / h (corresponding to 10% by mass with respect to polylactic acid). Next, polylactic acid and the filler and the compressible fluid were kneaded in the kneading area c to obtain a polylactic acid-based composition containing 3% by mass of the filler. Next, the compressible fluid in the extruder 11 is exhausted in the compressible fluid removal area d, and the polylactic acid-based composition containing 3% by mass of the filler is extruded into a strand shape and cooled in the molding processing area e, and then the cutter is used. I pelletized it. As a result, a polylactic acid foam containing a 3% by mass filler (master batch containing a 3% by mass filler) was obtained.

The temperature of each area is 190 ° C for the raw material mixing / melting area a and the compressible fluid supply area b, 150 ° C for the kneading area c, 190 ° C for the compressible fluid removal area d, and 190 ° C for the molding processing area e. did.

The pressure in each area was 7.0 MPa for the compressible fluid supply area b and the kneading area c, and 0.5 MPa for the compressible fluid removal area d.

In the obtained masterbatch, the number of coarse particles of 10 μm or more determined by the following measuring method was 20 particles / g.
-Number of coarse particles of filler-
50 mg of the masterbatch was remelted into a thin film of 10 μm. The obtained thin film was subjected to an optical microscope (manufactured by Nikon Corporation, FX-21, magnification 100 times) to count the number of coarse particles caused by a filler having a particle size of 10 μm or more. This operation was performed 5 times, and the average value was taken as the number of coarse particles of the filler.

(Making foam sheet)
Next, the continuous foam sheet forming apparatus 20 shown in FIG. 4 was used. The continuous foam sheet making device 20 includes a first extruder 21A and a second extruder 21B connected in series. (Preparation of masterbatch), the masterbatch containing 3% by mass filler obtained by the continuous kneading device 10 shown in FIG. 3 was supplied to the quantitative feeder 22A, and polylactic acid (Revode110, manufactured by HISUN, melting point 160 ° C.) was supplied. It was supplied to the quantitative feeder 22B. Then, a masterbatch containing a 3% by mass filler and polylactic acid were supplied to the raw material mixing / melting area a of the first extruder 21A so that the total flow rate of these was 10 kg / hr. The flow rate of the obtained masterbatch containing the 3% by mass filler was 1.67 kg / h, and the flow rate of polylactic acid was 8.33 kg / h so that the flow rate of the filler was 0.5% by mass.

Next, carbon dioxide, which is a compressible fluid, was supplied from the gas introduction unit 23A to the compressible fluid supply area b at a flow rate of 0.99 kg / h (corresponding to 10% by mass with respect to polylactic acid). Further, isocyanurate (Duranate TPA-100, Asahi Kasei Co., Ltd.), which is a cross-linking agent, was supplied from the gas introduction unit 23B so that the flow rate was 0.05 kg / h (0.5% with respect to the resin). ..

Then, the masterbatch containing 3% by mass of the filler, the polylactic acid and the cross-linking agent, and the compressible fluid were kneaded in the kneading area c and supplied to the second extruder 21B.

From the circular mold (slit diameter 70 mm) attached to the tip of the second extruder 21B, the mixture kneaded in the kneading area c is supplied into the second extruder 21B at a discharge rate of 10 kg / h, and the resin temperature is up to 140 ° C. While cooling, the mixture was kneaded in the second heating area d. Then, the compressible fluid is removed from the mixture and extruded and foamed, and the tubular polylactic acid-based foam sheet extruded and foamed from the slit 241 of the circular die 24 is placed along the cooled mandrel 25 and its outer surface is rolled. Air was blown from the air ring to cool and mold. Then, the polylactic acid-based resin foam sheet which had been cooled and molded was incised by a cutter to make a flat sheet, passed through a roller 26, and then wound by a take-up roller 27 to obtain a foam sheet.

The temperature of each area is 190 ° C. for the raw material mixing and melting area a and the compressible fluid supply area b of the first extruder 21A, 150 ° C. for the kneading area c, and the second heating area d of the second extruder 21B. Was 140 ° C.

The pressure in each area was 7.0 MPa from the compressible fluid supply area b to the second extruder heating area d.

<Examples 2 and 3>
In Example 1, the same procedure as in Example 1 was carried out except that the amount of filler was changed to the value shown in Table 1, and foam sheets of Examples 2 and 3 were prepared.

<Example 4>
A foamed sheet was prepared in the same manner as in Example 1 except that the type of the filler was changed to silica (QSG-30, manufactured by Shin-Etsu Chemical Co., Ltd., average particle diameter 0.004 μm).

<Examples 5 and 6>
A foamed sheet was prepared in the same manner as in Example 1 except that the type of the cross-linking agent was changed to a glycidyl ester-containing cross-linking agent (Joncryl 4368C, BASF).

<Example 7>
In Example 1, the same procedure as in Example 1 was carried out except that the feed was changed to 8 kg / Hr, to prepare a foamed sheet having a thickness of 0.8 mm.

<Comparative Example 1>
A foamed sheet was prepared in the same manner as in Example 1 except that the filler and the cross-linking agent were not included in Example 1.

<Comparative Example 2>
A foamed sheet was prepared in the same manner as in Example 1 except that the filler was changed to heavy calcium carbonate (Softon 2200, manufactured by Shiraishi Calcium Co., Ltd., number average particle diameter 1.000 μm). The average particle size of the number of fillers after kneading was 0.420 μm.

<Comparative Example 3>
In Example 5, the same procedure as in Example 5 was carried out except that the content of the cross-linking agent was changed, to prepare a foamed sheet.

Table 1 shows each component of the foamed sheet of each Example and Comparative Example.

<Physical characteristics>
Bulk density, average foam diameter, sheet thickness, buffer coefficient and piercing strength were measured as the physical properties of the obtained foamed sheet. The measurement results are shown in Table 1.

[Bulk density]
The bulk volume was determined from the external dimensions of the foamed sheet left for 24 hours or more in an environment of a temperature of 23 ° C. and a relative humidity of 50%. Then, the weight (g) of this foamed sheet was precisely weighed. As shown in the following formula (2), the bulk density was obtained by dividing the weight of the foam sheet by the bulk volume.
Bulk density = weight of foam sheet / bulk volume of foam sheet ... (2)

[Average foam diameter]
The obtained foam sheet was cross-sectioned with an ion milling device, and the cross-section was observed by SEM. The obtained cross-sectional SEM photograph (magnification 3000 times) uses the software of Image-Pro Premier (manufactured by media) to binarize the gray component and the resin component (white) corresponding to foaming (voids), and 35 μm × The average particle diameter (ferred diameter) was determined in the range of 20 μm, and the average foam diameter was calculated for the gray component (foaming) having a ferret diameter of 0.5 μm or more. The average foam diameter was the average value of foam at three locations.

[Sheet thickness]
The obtained foam sheet was cross-sectioned with an ion milling device, and the cross-section was observed by SEM. Image-Pro Premier (manufactured by mediay) software was used in the obtained cross-sectional SEM photograph (magnification 100 times). Then, the range of 1 mm as one field of view was measured 10 times, and the average value of one field of view was calculated. This was done in 3 fields of view, and the average value of the 3 fields of view was taken as the sheet thickness.

[Contents of residual volatile components]
2 parts by mass of 2-propanol was added to 1 part by mass of the obtained foamed sheet, dispersed by ultrasonic waves for 30 minutes, and then stored in a refrigerator (5 ° C.) for 1 day or more to extract volatile components in the composition. .. The supernatant of the stored dispersion was analyzed by gas chromatography (GC-14A, manufactured by Shimadzu Corporation), and the volatile components in the composition were quantified and measured. As a reference, polylactic acid resin (Revode110) is measured by the same procedure, and if it is below the reference, it is regarded as the lower limit of detection. When the volatile component was below the lower limit of detection, it was evaluated as 〇, and when the volatile component exceeded the lower limit of detection, it was evaluated as x.
(Measurement condition)
・ Equipment: GC-14A (manufactured by Shimadzu Corporation)
-Column: CBP20-M 50-0.25
-Detector: FID
・ Injection amount: 1 μL to 5 μL
-Carrier gas: He 2.5 kg / cm ²
・ Hydrogen flow rate: 0.6 kg / cm ²
・ Air flow rate: 0.5 kg / cm ²
・ Chart speed: 5 mm / min
-Sensitivity: Range101 x Atten20
-Column temperature: 40 ° C
-Injection Temp: 150 ° C

[Cushioning property]
The cushioning property of the obtained foamed sheet was evaluated by the buffering coefficient.
In determining the buffer coefficient, first, the compressive stress was measured. As a compressive stress measuring device, a universal testing machine (AG-50X, manufactured by Shimadzu Corporation) and a 5 kN calibrated load cell were used. A circle with a diameter of 50 mm was evenly punched from the sheet. At this time, the required number of sheets is punched out so that the thickness of the sheet becomes 25 mm to 35 mm when a sample is sandwiched between the pressure plate and the support plate fixed to the universal testing machine and a force of 2.9 N to 3.0 N is applied. rice field. The sheet was sandwiched between the pressure plate and the support plate and pressed to (40 ± 1)% of the thickness of the test piece at a speed (100 ± 20) mm / min. When the stress did not reach 0.3 MPa, the amount of compression was changed to 70% of the thickness. Then, based on the first measured value of the compressive stress at that time, the buffer coefficient was obtained according to JIS Z 0235: 2002 and ISO4651. The above operation was repeated 3 times, and the average value of the buffer coefficient 3 times was obtained. The average value of the obtained three buffering coefficients was evaluated as the buffering coefficient of the foamed sheet according to the following evaluation criteria. The cushioning coefficient is 0. When the compressive stress exceeds 0.02 MPa and is 0.05 MPa or less (compressive stress A) and when the compressive stress exceeds 0.05 MPa and is 0.2 MPa or less (compressive stress B). It was measured when it exceeded 2 MPa and was 0.3 MPa or less (compressive stress C).
Buffer coefficient = compressive stress / compressive energy per unit volume ・ ・ ・ (3)
(Evaluation criteria)
⊚: The cushioning coefficient is 10 or less for each of the compressive stresses A, B and C.
〇: The buffer coefficient is 10 or less for the compressive stresses A and B, but the buffer coefficient is not 10 or less for the compressive stress C.
Δ: The cushioning coefficient is 10 or less at the compressive stress A, but the buffer coefficient is not 10 or less at the compressive stresses B and C.
X: The cushioning coefficient is not 10 or less at the compressive stresses A, B, and C.

[Puncture strength]
The puncture strength was determined according to JIS Z 1707 using a sample having a foam sheet thickness of 2 mm. The sheet strength of the foamed sheet was evaluated from the piercing strength.

From Table 1, the foam sheets obtained in Examples 1 to 6 satisfy the above-mentioned conditions (the piercing strength is 2N or more and the buffering property is ⊚ or 〇) in both the piercing strength and the cushioning property. It was confirmed that. On the other hand, the foamed sheets obtained in Comparative Examples 1 to 3 did not satisfy at least one of the above-mentioned conditions in terms of puncture strength and cushioning property, resulting in unacceptable deterioration in quality. Therefore, it was confirmed that the foamed sheets obtained in Comparative Examples 1 to 3 could not have all the required properties at the same time and had a problem in practical use.

Therefore, unlike the foam sheets of Comparative Examples 1 to 3, the foam sheets of Examples 1 to 6 have a compressive stress of 0.2 MPa or less and a sheet thickness of 2 mm, which has a cushioning coefficient of 10 or less, and JIS Z 1707. The piercing strength obtained in is 2.4N or more. Thereby, the foamed sheets of Examples 1 to 6 can have excellent cushioning properties and sheet strength.

As described above, the embodiments have been described, but the above embodiments are presented as examples, and the present invention is not limited to the above embodiments. The above embodiment can be implemented in various other embodiments, and various combinations, omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

10 Continuous kneading device 20 Continuous foam sheet making device

Japanese Unexamined Patent Publication No. 2012-030571

Claims (14)

Contains polylactic acid and fillers
The compressive stress when the buffer coefficient is 10 or less is 0.2 Mpa or less, and
A foamed sheet having a piercing strength of 2N or more when the sheet thickness is 2 mm. The foamed sheet according to claim 1, wherein the compressive stress is 0.05 Mpa or less. The foamed sheet according to claim 1 or 2, wherein the puncture strength is 5 N or less. The foamed sheet according to any one of claims 1 to 3, wherein the puncture strength is 3N or more. The foamed sheet according to any one of claims 1 to 4, wherein the sheet thickness is 1 mm to 10 mm. The foamed sheet according to any one of claims 1 to 5, wherein the bulk density is 0.025 g / cm ³ to 0.250 g / cm ³ . The foamed sheet according to any one of claims 1 to 6, which does not substantially contain an organic compound having a boiling point of −20 ° C. or higher and lower than 150 ° C. The foamed sheet according to any one of claims 1 to 7, wherein the content of the polylactic acid is 98% by mass or more with respect to the total amount of organic substances in the foamed sheet. The foamed sheet according to any one of claims 1 to 8, wherein the content of the filler is 0.1% by mass to 5.0% by mass. A product comprising the foam sheet according to any one of claims 1 to 9. The product according to claim 10, which is at least one selected from bags, packaging containers, tableware, cutlery, stationery and cushioning materials. A kneading step of kneading polylactic acid and a filler at a temperature lower than the melting point of the polylactic acid in the presence of a compressible fluid to obtain a polylactic acid-based composition.
A foaming step of foaming the polylactic acid-based composition to obtain a foamed sheet when the compressible fluid is removed from the polylactic acid-based composition, and a foaming step.
A method for manufacturing a foamed sheet including. The method for manufacturing a foamed sheet according to claim 12, wherein the foamed sheet is the foamed sheet according to any one of claims 1 to 9. The method for producing an effervescent sheet according to claim 12 or 13, wherein the compressible fluid is carbon dioxide.

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