JP2021116412A - Foam sheet, product, and method for producing foam sheet - Google Patents

Abstract

To provide a foam sheet excellent in strength.SOLUTION: A foam sheet contains an aliphatic polyester resin, and a filler. A degree of hydrophobicity of the filler is 50 mass% or more, and a pH of the filler is 6.5 or less.SELECTED DRAWING: None

Description

The present invention relates to an effervescent sheet, a product, and a method for producing an effervescent sheet.

Plastic products are processed into various shapes such as bags and containers and are widely distributed. However, since the plastic product has a property of being difficult to be decomposed in the natural world, disposal of the plastic product after use has become a problem. Therefore, materials for replacing non-degradable plastics, which are difficult to be decomposed in nature, with biodegradable plastics, which are decomposed in nature, are being actively developed for the plastic products.

As a biodegradable plastic, an aliphatic polyester having biodegradability is attracting attention.
In order to widely use the aliphatic polyester, a foamed sheet in which the aliphatic polyester is foamed to reduce the amount of the aliphatic polyester has been proposed (see, for example, Patent Documents 1 to 4).

An object of the present invention is to provide a foamed sheet having excellent strength.

The foamed sheet of the present invention as a means for solving the above-mentioned problems contains an aliphatic polyester resin and a filler, and contains an aliphatic polyester resin and a filler.
The degree of hydrophobization of the filler is 50% by mass or more, and the degree of hydrophobization is 50% by mass or more.
The filler has a pH of 6.5 or less.

According to the present invention, it is possible to provide a foamed sheet having excellent strength.

FIG. 1 is a phase diagram showing the state of matter with respect to temperature and pressure. FIG. 2 is a phase diagram for defining the range of the compressible fluid. FIG. 3 is a schematic view showing an example of a continuous kneading device used for producing the aliphatic polyester resin composition of the present invention. FIG. 4 is a schematic view showing an example of a continuous foaming apparatus used for manufacturing the foamed sheet of the present invention.

(Effervescent sheet)
The foamed sheet of the present invention contains an aliphatic polyester resin (hereinafter, also referred to as "aliphatic polyester") and a filler, and further contains other components as necessary.

In general, it is known that aliphatic polyesters such as polylactic acid are difficult to be molded. Therefore, it is proposed in Japanese Patent Application Laid-Open No. 2007-46019 to modify polylactic acid and a polylactic acid sheet by mixing polylactic acid with another resin. However, in the above proposal, by mixing polylactic acid with another resin, the other resin is not easily biodegradable, so that the resin is not easily biodegradable as a whole.

A foamed sheet in which a resin is foamed is preferable in that the amount of resin used can be reduced and the weight can be reduced. However, in order to achieve both strength and flexibility of the foamed sheet, it is necessary to uniformly and finely disperse the foamed diameter. be.
The fine foam material disclosed in Japanese Patent No. 5207277 uses carbon dioxide in a supercritical state as a foaming agent and has a foam diameter of 1 μm or less. Since carbon dioxide in a supercritical state has a structure similar to that of an aliphatic polyester skeleton, it has a high affinity with an aliphatic polyester resin and is said to be suitable as a foaming agent. However, this proposal can only be manufactured in batch equipment and cannot be industrially mass-produced in a continuous process.
Generally, it is known that the viscosity of an aliphatic polyester resin having crystallinity decreases sharply once it is melted, and foam rupture and coalescence of foams are likely to occur, so that the foam diameter is made finer and more uniform. It's difficult in the first place.

The inventor has studied to obtain a polylactic acid foamed sheet that can be mass-produced industrially and has fine and uniform foaming that can solve the above problems. As a result, they have found that a foamed sheet containing a large amount of an aliphatic polyester resin having uniform and fine foaming can be obtained by adjusting the degree of hydrophobicity and pH of the filler, and the present invention has been completed.

<Alphatic polyester resin>
Since the aliphatic polyester resin is biodegraded by microorganisms (biodegradable resin), it is attracting attention as an environment-friendly low environmental load polymer material (“Structure, physical properties, biodegradable polymer 2001 of aliphatic polyester”. See Vol. 50, No. 6, p374-377 ").
Examples of the aliphatic polyester resin include polylactic acid, 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. Among these, polylactic acid, which is a carbon-neutral material and is relatively inexpensive, is preferable.

Examples of the polylactic acid include a copolymer of D-lactic acid and L-lactic acid, a homopolymer of either D-lactic acid (D form) or L-lactic acid (L form), and D-lactide (D form). ), L-lactide (L-form) and a ring-opening polymer of one or more lactides selected from the group consisting of DL-lactide. 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 crystallinity is related to the heat resistance of the foamed sheet and the molding temperature of foaming, it may be used properly according to the application, and is not particularly limited. The crystallinity here expresses the crystallinity and the crystallization rate, and the high crystallinity means that the crystallinity is high and / or the crystallization rate is high.
As the polylactic acid, an appropriately synthesized one or a commercially available one may be used.

From the viewpoint of biodegradability, the content ratio of the aliphatic polyester resin is preferably 80% by mass or more, more preferably 99% by mass or more, based on the total amount of organic substances in the foamed sheet.

<Measuring method of content ratio of aliphatic polyester resin>
The content ratio of the aliphatic polyester resin can be calculated from the ratio of the materials to be charged. If the material ratio is unknown, for example, the following GCMS analysis can be performed, and the components can be specified by comparison using a known aliphatic polyester resin as a standard sample. If necessary, it is possible to calculate the area ratio of the spectrum by NMR measurement and other analysis methods in combination.
-Measurement by GCMS analysis-
・ GCMS: Shimadzu Corporation QP2010 Auxiliary Equipment Frontier Lab Py3030D
-Separation column: Frontier Lab Ultra ALLOY UA5-30M-0.25F
-Sample heating temperature: 300 ° C
-Column oven temperature: 50 ° C (hold for 1 minute) -rise temperature 15 ° C / min-320 ° C (6 minutes)
-Ionization method: Electron Ionization (EI) method-Detected mass range: 25 to 700 (m / z)

<Filler>
The filler (hereinafter, also referred to as “foam core material”) is contained in order to adjust the foaming state (size, amount, arrangement of foam) of the foamed sheet.
Examples of the filler include inorganic fillers and organic fillers. These may be used alone or in combination of two or more.
Examples of the inorganic filler include talc, kaolin, calcium carbonate, layered silicate, zinc carbonate, wallastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, and sodium aluminate. Examples thereof include magnesium silicate, glass balloon, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate, boron nitride, graphite, glass fiber and carbon fiber.
Examples of the organic filler include naturally occurring polymers such as starch, cellulose fine particles, wood flour, okara, fir husks, and bran, modified products thereof, sorbitol compounds, benzoic acid, metal salts of the compounds, and phosphoric acid esters. Examples include metal salts and rosin compounds.
Among these, silica, which is an inorganic nucleating agent, is preferable because it has a high affinity with a compressible fluid described later. When a filler other than silica is used as a base, a filler surface-treated with silica is preferable.

Silica contains _{silicon dioxide represented by SiO 2} as a main component. The silica particles are roughly classified into two types, dry silica and wet silica, according to the method for producing silica particles. In the present invention, any of the methods produced can be used.

Silica is preferably surface-treated with a reactive compound such as a silane coupling agent, a titanate coupling agent, or an organosiloxane, if necessary.
In particular, a silane coupling agent can be suitably used for surface treatment of silica particles, and specific examples of the silane coupling agent include, for example, vinyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxy. Examples thereof include propyltrimethoxysilane, γ-aminopropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

The content ratio of silica is preferably 50% by mass or more with respect to the total amount of inorganic substances in the foamed sheet, regardless of whether a filler surface-treated with silica is used or a filler other than silica is used in combination with silica. , 60% by mass or more is more preferable. When the silica content is 50% by mass or more, the foaming becomes uniform and fine.

The average particle size of the number of fillers is preferably 5 nm (0.005 μm) to 100 nm (0.1 μm), more preferably 0.01 μm to 0.08 μm. If the number average particle size is less than 5 nm (0.005 μm), the dispersibility of silica is poor, and the resulting foamed sheet may have reduced sheet physical properties such as impact strength, and the average particle size. If it exceeds 100 nm (0.1 μm), the surface appearance of the obtained foamed sheet may be inferior.

The average particle size of the filler may be expressed by the BET specific surface area assuming that the filler is a true sphere for convenience. Its BET specific surface area in becomes ^{23m 2} / ^g~230m 2 / g.
(BET specific surface area (m ² / g) = specific surface area of one particle / weight of one particle = 3 / (average diameter / 2) x true specific gravity = 3 / (average diameter / 2) / (true specific gravity x 10 ⁶⁾ )
※ particles one weighing :( average diameter ^{/ 2) 3 × 4/3} × 3.14 × true density ^{(2.65) × 10 6 (g} / piece)
* Specific surface area of one particle (average diameter / 2) ² x 4 x 3.14

The standard deviation (σ) of the number average particle size of the filler is preferably 3 times or less, more preferably 2 times or less, based on the number average particle size. When the standard deviation (σ) is within the above range, the foaming of the foamed sheet is uniform.
There is a correlation between the standard deviation of the filler and the standard deviation of foaming. That is, if the standard deviation of the filler is within the above range, it can be said that the foaming is uniform.

The proportion of coarse particles of the filler having a particle size of 10 μm or more is preferably 100 or less, more preferably 40 or less per 1 g of the foamed sheet. When the number of coarse particles is 100 or less, the foam diameter is fine and the physical properties such as appearance and strength are good.

To measure the proportion of coarse particles, remelt 50 mg of foamed sheet into a thin film of 10 μm, and use an optical microscope (Nikon, FX-21, magnification 100 times) to make a filler with a particle size of 10 μm or more. It can be measured by counting the number of coarse particles caused by it.

The degree of hydrophobization of the filler is 50 wt% (mass%) or more, preferably 60 wt% or more. The degree of hydrophobization here refers to the degree of methanol hydrophobization. If the degree of hydrophobization is less than 50 wt%, not only the hygroscopicity is increased and the filler is aggregated in the aliphatic polyester, but also when the filler is introduced into the aliphatic polyester, the aliphatic polyester is hydrolyzed by water. It is not preferable because it causes side effects such as receiving.

The degree of hydrophobization is determined by dropping methanol while stirring while 1 g of the filler is suspended on the surface of 50 ml of pure water, and determining the amount of methanol required to suspend the entire amount of the filler in pure water in% by weight. It can be measured by.

The pH of the filler is 6.5 or less, preferably 3.5 to 6, and more preferably 4 to 6. The pH of the filler here refers to the pH of the surface of the filler obtained in a 4% dispersion of the filler (water: methanol = 1: 1). If the pH exceeds 6, the fillers may aggregate with each other. If the pH is less than 3.5, the aliphatic polyester may be decomposed.
The reason why the pH of the filler is in the above range is as follows. When carbon dioxide is used as a foaming agent, if carbon dioxide is used as a dispersion medium for the filler, it is considered that particles are likely to aggregate at the (isoelectric point) of the filler dispersion. _{This is because CO 2} is essentially electrophilic as shown by the values of carbon dioxide ionization potential of 13.7 eV and electron affinity of 3.8 eV, and it is considered that the surface state of the filler optimal for dispersion exists.

The pH is obtained by preparing a suspension of 4% effervescent nucleating agent (water / methanol = 1: 1 vol / vol) and measuring the pH of the prepared suspension.

In the evaluation of the filler such as the degree of hydrophobicity and pH described above, even after the foamed sheet is manufactured, the foamed sheet is dissolved with a solvent, the aliphatic polyester resin component is filtered off, the filler is taken out, and the obtained filler is used. It can also be obtained by analyzing.
Further, when evaluating the filler of the obtained foamed sheet, a preliminary operation may be performed in which the foamed sheet is burned in an electric furnace or the like and taken out as ash.

The content of the filler can be appropriately selected depending on the intended purpose as long as the physical properties of the foamed sheet are not impaired, but is preferably 0.1% by mass to 10% by mass, and 0.5% by mass, based on the entire foamed sheet. More preferably, it is by mass% to 5% by mass. When the content of the filler is 0.1% by mass to 10% by mass, it is possible to prevent the problem that the fillers aggregate with each other.

<Other ingredients>
The other components are not particularly limited as long as they are usually contained in the foamed sheet, and can be appropriately selected depending on the intended purpose. Examples thereof include a cross-linking agent.
As the cross-linking agent, since it is highly reactive with the polylactic acid resin, the monomer is unlikely to remain, and the resin is less colored, it has two or more (meth) acrylic groups in the molecule or one or more (meth) acrylic groups. ) A (meth) acrylic acid ester compound having an acrylic group and one or more glycidyl groups or vinyl groups is preferable.
Specific examples of these compounds include glycidyl methacrylate, glycidyl acrylate, glycerol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropanetriacrylate, allyloxypolyethylene glycol monoacrylate, allyloxypolyethylene glycol monomethacrylate, and polyethylene glycol dimethacrylate. Polyethylene glycol diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polytetramethylene glycol dimethacrylate, and alkylene copolymers in which these alkylene glycol portions have various lengths may be used, and butanediol methacrylate and butanediol acrylate may be used. And so on.

By containing a cross-linking agent, melt tension can be applied and the foaming ratio of the foamed polylactic acid sheet can be adjusted. A method of dispersing a foam nucleating agent 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, or 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, and the like.
In addition to the above, other components include additives such as heat stabilizers, antioxidants, and plasticizers. These may be used alone or in combination of two or more.

The content ratio of other components is preferably 20% by mass or less, more preferably 10% by mass or less, based on the total amount of organic substances in the foamed sheet, from the viewpoint of recyclability.

<Physical characteristics of foam sheet>
The average foam diameter of the foamed sheet of the present invention is preferably 15 μm or less, more preferably 7 μm or less. The average foam diameter is preferably 0.1 μm or more.
If the average foam diameter is 15 μm or more, the strength of the foam sheet may decrease.

The method for measuring the average foam diameter of the foamed sheet is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the foamed sheet is cross-sectioned with an ion milling device and SEM observation of the cross section is performed. Can be measured with. ..
The obtained cross-sectional SEM photograph (magnification of 3,000 times) was obtained by binarizing the gray component and the resin component (white) corresponding to foaming (voids) using software of Image-Pro Premier (manufactured by media). The average particle diameter (ferred diameter) is obtained in the range of 35 μm × 20 μm, and the average foamed diameter is calculated for the gray component (foaming) having a ferret diameter of 0.5 μm or more.

The bulk density of the foam sheet is preferably 0.1 g / cm ³ or more 0.9 g / cm ³ or less, more preferably 0.7 g / cm ³ or less, 0.5 g / cm ³ or less is more preferable.
When the bulk density of the foamed sheet is within this range, a foamed sheet having an excellent balance between strength and lightness can be obtained.

As a method for measuring the bulk density of the foamed sheet, for example, it can be measured as follows.
The bulk volume is obtained 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%. Next, the weight (g) of this foamed sheet is precisely weighed. The bulk density is obtained by dividing the weight of the foam sheet by the bulk volume.

The foamed sheet of the present invention may be used as a product described later, may be used by printing on the sheet as it is, or may be used in a process of processing using a mold to obtain a product.
The method for processing the sheet using the mold is not particularly limited, and a conventionally known method of thermoplastic resin can be used, and examples thereof include vacuum forming, compressed air molding, vacuum pressure air forming, and press molding.

(Product)
The product of the present invention comprises the foamed sheet of the present invention and, if necessary, other components.
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”) include bags, packaging containers, trays, tableware, cutlery, stationery, and cushioning materials as daily necessities. 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 the stationery include clear files and emblems.

Since the conventional foamed sheet has a large foaming 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 molded using the foamed sheet of the present invention has excellent physical properties, it can be applied to applications other than the above-mentioned daily necessities, for example, industrial materials, agricultural products, food products, pharmaceutical products, cosmetics, etc. It can be widely applied as a sheet, packaging material, etc.

The foamed sheet of the present invention is useful for applications that make the best use of the biodegradability of the foamed sheet, especially as a packaging material used for foods, cosmetics, medical sheets for pharmaceuticals, etc., and further improvement in performance can be expected by thinning the film. ..

(Manufacturing method of foam sheet)
The method for producing a foamed sheet of the present invention includes a kneading step and a foaming step, and further has other steps as needed.
The kneading step and the foaming step may be carried out at the same time or as separate steps.

<Kneading process>
The kneading step is a step of kneading the aliphatic polyester resin and the filler at a temperature lower than the melting point of the aliphatic polyester resin in the presence of a compressible fluid.
In the kneading step, a foaming agent may be added in addition to the aliphatic polyester resin and the filler in order to promote foaming more efficiently.
The mixture of the aliphatic polyester resin, the filler, and the foaming agent before foaming may be referred to as a polylactic acid composition or a masterbatch.

<< Foaming agent >>
As the foaming agent, hydrocarbons such as lower alkanes such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane, and ethers such as dimethyl ether, in that a polylactic acid resin foam sheet having a high expansion ratio can be easily obtained. , Hydrocarbons such as methyl chloride and ethyl chloride, and physical foaming agents such as compressible gases such as carbon dioxide and nitrogen.
Among these, it is preferable to use a compressible gas such as carbon dioxide or nitrogen from the viewpoint of having no odor, being safe to handle, and having a low environmental load.

Since the aliphatic polyester has a property that the melt viscosity drops sharply after the melting point, the filler tends to aggregate when the filler (filler) or the like is kneaded. The effect is remarkable when the size of the filler is small.
In the present invention, in order to uniformly disperse the filler in this polylactic acid, kneading is performed using a compressible fluid. When the compressible fluid is the same as the foaming agent, filler kneading and foaming can be carried out in a series of processes, which is more preferable as a production form from the viewpoint of reducing the environmental load.

The reason why it is preferable to use a compressed fluid for kneading the fine filler and the aliphatic polyester resin will be described below.
It is generally known that a compressible fluid plasticizes a resin and lowers the melt viscosity of the resin (see "Latest Applied Technology for Supercritical Fluids", NTS). At first glance, there seems to be a contradiction between lowering the melt viscosity and improving kneadability. In fact, in general filler kneading, pressure may be applied without using a compressible fluid, but this is aimed at reducing the free volume of the resin and increasing the interaction between the resins (increasing viscosity). Yes, plasticization of the resin is counterproductive (see "k. Yang. R. Ozisk R. Polymer, 47.2849 (2006)").

So far, it is known that a compressible liquid has a property of plasticizing (softening) a resin, and when the temperature of the compressible liquid is raised, the resin becomes like a liquid. 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, so that a highly dispersed resin composition cannot be obtained. That is, it has been considered difficult to use a compressible liquid for kneading the resin and the filler because the viscosity of the resin is not suitable for kneading in the presence of the compressible fluid.
Therefore, as a result of diligent studies on whether the compressible fluid can be used for kneading the aliphatic polyester resin and the filler, the present inventors diligently studied whether the temperature is lower than the melting point of the aliphatic polyester resin in the presence of the compressible fluid. , It was found that the viscosity of the aliphatic polyester resin becomes suitable for kneading, and the filler can be kneaded. In particular, the aliphatic polyester resin whose melt viscosity drops sharply above the melting point can be kneaded only in a low melt viscosity state, whereas in the present invention, the filler can be kneaded in a high viscosity state. Further, it is more preferable because a compressible fluid can be used as a foaming agent as it is.

<< Compressible fluid >>
Examples of substances 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, and dimethyl ether. .. Among these, carbon dioxide is preferable in that 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 aliphatic polyester resin composition will be described with reference to FIGS. 1 and 2. FIG. 1 is a phase diagram showing the state of matter with respect to temperature and pressure. FIG. 2 is a phase diagram for defining the range of the compressible fluid. The “compressible fluid” in the present embodiment means that the substance exists in any of the regions (1), (2), and (3) shown in FIG. 2 in the phase diagram shown in FIG. It means the state of time.

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

Since the solubility of the compressible fluid changes depending on the combination of the resin type and the compressible fluid, the temperature, and the pressure, it is necessary to appropriately adjust the supply amount of the compressible fluid.
For example, in the case of a combination of polylactic acid and carbon dioxide, 2% by mass or more and 30% by mass or less is preferable. When the amount of carbon dioxide supplied is 2% by mass or more, it is possible to prevent the problem that the effect of plasticization is limited. When the supply amount of carbon dioxide is 30% by mass or less, it is possible to prevent a problem that carbon dioxide and polylactic acid are phase-separated and a foamed sheet having a uniform thickness cannot be obtained.

<< Kneading device >>
As the kneading device used for producing the aliphatic polyester resin 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-axis cage type stirring tank, Sumitomo Heavy Industries, Ltd. Bivolac, and Mitsubishi Heavy Industries, Ltd. N- SCR, Hitachi, Ltd. glasses wing, lattice wing or Kenix type, Sulzer type SMLX type static mixer equipped tube type polymerization tank, etc. can be used. In terms of color tone, self-cleaning polymerization equipment such as finishers, N-SCRs, and biaxial extrusion ruders 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.

Here, as shown in FIG. 3, the continuous kneading device 100 uses a twin-screw extruder (manufactured by JSW) (screw diameter 42 mm, L / D = 48, device 1), (raw material mixing / melting area). It is composed of a, device 2), (compressible fluid supply area b, device 3), kneading area c, molding area d, and T-die 4. Compressible fluid (liquid material) is supplied by a metering pump. Solid raw materials such as resin pellets and calcium carbonate are supplied by a quantitative feeder.

<< Raw material mixing / melting area >>
In the raw material mixing / melting area, resin pellets and fillers are mixed and the temperature is raised. The heating temperature is set to be equal to or higher than the melting temperature of the resin so that it can be uniformly mixed with the compressible fluid in the area where the compressible fluid is subsequently supplied.

<< Compressible fluid supply area >>
The resin pellets are in a molten state by heating, and in a state where the filler is wet, a compressible fluid is supplied to plasticize the molten resin.

<< Kneading area >>
The temperature of the kneading area is set so that the viscosity is suitable for kneading the filler. The set temperature is not particularly limited because it changes depending on the specifications of the reactor, the resin type, the structure of the resin, the molecular weight, etc., but in the case of commercially available polylactic acid having a weight average molecular weight (Mw) of about 200,000, Normal kneading is carried out at the melting point of polylactic acid + 10 ° C to 20 ° C. On the other hand, the present invention is characterized in that it is kneaded at a temperature lower than the melting point of polylactic acid, and can be kneaded at a relatively high viscosity at a temperature lower than the melting point. Specifically, it is −20 ° C. to −80 ° C., more preferably −30 ° C. to −60 ° C. For convenience, the temperature may be set with reference to the current value of the stirring power of the apparatus as a guide, but it can be said that these set values are in a range that cannot normally be reached without the present invention.

<Foam process>
The foaming step is a step of removing the compressible fluid to foam the polylactic acid composition.
The compressible fluid can be removed by releasing the pressure.
As the temperature in the foaming step, it is preferable to heat the polylactic acid resin to a temperature equal to or higher than the melting point.

In the foaming step, the compressible fluid dissolved in the polylactic acid composition vaporizes at the interface with the filler in response to an operation of changing the solubility of the compressed fluid such as depressurization and heating, and foaming occurs. Since foaming starts from the filler, a foamed sheet having uniform and fine foaming can be produced only when the filler is uniformly dispersed in 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. Examples thereof include a molding step of processing into a sheet.
Examples of the molding step include vacuum forming, compressed air forming, press molding and the like. A sheet molded product is obtained by the molding step.

Hereinafter, examples of the present invention will be described, but the present invention is not limited to these examples.

(Example 1)
<Making foam sheet>
<< Preparation of masterbatch >>
Using the continuous kneading apparatus 100 shown in FIG. 3, the raw material mixing / melting area a was supplied so that the total flow rate of the polylactic acid resin as the aliphatic polyester resin and the filler was 10 kg / hr. Polylactic acid (REVODE110, manufactured by HISUN, melting point 160 ° C.) 9.7 kg / hr, silica particles as filler (AEROSILR202 manufactured by Aerosil Japan) 0.3 kg / hr, and carbon dioxide 0.97 kg / hr as a compressible fluid. h (equivalent to 10% by mass based on polylactic acid) is supplied to the compressible fluid supply area b, kneaded in the kneading area c, and an aliphatic polyester resin composition containing 3% by mass of filler (3% by mass filler master). Batch) was prepared.
The temperatures of each zone were raw material mixing / melting area a and compressible fluid supply area b: 190 ° C., kneading area c: 150 ° C., compressible fluid removal area d: 190 ° C., and molding processing area e: 190 ° C. The pressure in each zone is 7.0 MPa from the compressible fluid supply area b to the kneading area c and 0.5 MPa in the compressible fluid removal area d, and the pressure is extruded in a strand shape, cooled in a water bath, and then pelletized with a strand cutter. A masterbatch containing 3% by mass of filler was obtained.

<< Preparation of foam sheet >>
Using the continuous foam sheet forming apparatus 110 shown in FIG. 4, the 3 mass% filler masterbatch and the polylactic acid resin (Revode 110, manufactured by HISUN) were supplied so as to have a total flow rate of 10 kg / hr. As a ratio of the obtained 3% by mass filler masterbatch 1.67 kg / hr and polylactic acid (REVODE110, manufactured by HISUN, melting point 160 ° C.) 8.33 kg / hr so that the filler becomes 0.5% by mass. Carbon dioxide was supplied as a compressible fluid at 0.99 kg / h (corresponding to 10% by mass with respect to polylactic acid), kneaded, and subjected to the second extruder 4.
A circular mold with a slit diameter of 70 mm attached to the tip of the second extruder is cooled to a discharge rate of 10 kg / h and a resin temperature of 167 ° C., and compressed from an aliphatic polyester resin composition kneaded in the second extruder heating area d. By removing the fluid, the foam is extruded and foamed, and the tubular foam sheet extruded from the mold slit is placed along the cooled mandrel, and the outer surface is cooled and molded by blowing air from the air ring. An incision was made with a cutter to form a flat sheet, and a foamed sheet was obtained.
The temperature of each zone is as follows: first extruder: raw material mixing / melting area a and compressible fluid supply area b: 190 ° C., kneading area c: 150 ° C., second extruder heating area d: 167 ° C. The pressure in each zone was 7.0 MPa from the compressible fluid supply area b to the kneading area c and the second extruder heating area d.

(Examples 2 to 3, Examples 11 to 12, Comparative Examples 1 to 2)
In Example 1, the foam sheets of Examples 2 to 3, Examples 11 to 12, and Comparative Examples 1 to 2 were prepared in the same manner as in Example 1 except that the type of silica as a filler was changed to the following. Made.
Example 2: AEROSIL R816 (manufactured by Aerosil Japan)
Example 3: AEROSIL NY50 (manufactured by Aerosil Japan)
Example 11: A mixture of AEROSIL R202 (manufactured by Aerosil Japan Co., Ltd.) and SG-2000 (manufactured by Japan Talc Co., Ltd.) (weight ratio 50:50)
Example 12: A mixture of AEROSIL R202 (manufactured by Aerosil Japan Co., Ltd.) and SG-2000 (manufactured by Japan Talc Co., Ltd.) (weight ratio 80:20)
Example 15: QSG-100 (manufactured by Shin-Etsu Chemical Co., Ltd.)
Comparative Example 1: HDK-2000H (manufactured by Clariant)
Comparative Example 2: AEROSIL MOX170 (manufactured by Aerosil Japan)

(Examples 4 to 5)
In Example 1, foam sheets of Examples 4 to 5 were produced in the same manner as in Example 1 except that the amount of filler was changed as shown in Table 1.

(Example 6)
In Example 1, the aliphatic polyester resin was changed to polylactic acid (Revode 190, manufactured by HISUN, melting point 175 ° C.), and the compressed fluid was carbon dioxide 0.78 kg / h (8% by mass based on polylactic acid) and dimethyl ether. A foamed sheet of Example 6 was prepared in the same manner as in Example 1 except that the value was changed to 0.19 (2% by mass based on polylactic acid).

(Example 7)
In Example 1, the foamed sheet of Example 7 was obtained in the same manner as in Example 1 except that the aliphatic polyester resin was changed to polylactic acid (Revode 101, manufactured by HISUN, melting point 150 ° C.).

(Example 8)
In Example 1, the foamed sheet of Example 8 was obtained in the same manner as in Example 1 except that the aliphatic polyester resin was changed to polybutylene succinate (manufactured by PTT MCC Biochem, melting point 115 ° C.).

(Example 9)
In Example 1, the aliphatic polyester resin was changed to polyglycolic acid (PGA) (manufactured by Kureha Corporation, kuredux100E35, melting point 220 ° C.). Further, in Example 1, the compressible fluid used for preparing the master batch and the foamed sheet was 0.25 kg / h of carbon dioxide as the first compressible fluid and dimethyl ether as the second compressible fluid. The foamed sheet of Example 9 was supplied at 0.25 kg / h, and the temperature of each zone was changed to the raw material mixing / melting area a and the compressible fluid supply area b: 230 ° C. in the same manner as in Example 1. Got

(Example 10)
In Example 1, the aliphatic polyester resin is prepared by using polylactic acid (REVODE110, manufactured by HISUN, melting point 160 ° C.), which is an aliphatic polyester, and John Krill (BASF), which is a styrene-acrylic cross-linking agent which is not an aliphatic polyester. A foamed sheet of Example 10 was obtained in the same manner as in Example 1 except that the resin was changed to a resin contained at a ratio of 99: 1.

(Example 13)
In Example 1, the aliphatic polyester resin is composed of polylactic acid (REVODE110, manufactured by HISUN, melting point 160 ° C.), which is an aliphatic polyester, and polystyrene (PS Japan, HF77), which is not an aliphatic polyester, at a ratio of 80:20. A foamed sheet of Example 14 was obtained in the same manner as in Example 1 except that the resin contained in the above was changed.

(Example 14)
In Example 1, the aliphatic polyester resin is composed of polylactic acid (REVODE110, manufactured by HISUN, melting point 160 ° C.), which is an aliphatic polyester, and polystyrene (PS Japan, HF77), which is not an aliphatic polyester, at a ratio of 50:50. A foamed sheet of Example 14 was obtained in the same manner as in Example 1 except that the resin contained in the above was changed.

The average particle size, degree of hydrophobicity, and pH of the fillers in the obtained foamed sheet were measured by analyzing the fillers taken out as ash from the foamed sheet. The ash content is a residue when burned at 600 ° C. for 4 hours.
The ash content was measured as follows.
About 3 g of the foamed sheet sample was weighed into a 100 mL crucible whose weight was precisely weighed to the fourth decimal place with a precision balance, and the total weight of the crucible and the sample was precisely weighed.
The crucible was placed in a muffle furnace FP-310 manufactured by Yamato Scientific Co., Ltd. and burned at 600 ° C. for 4 hours to burn organic components. Then, the crucible was cooled in the desiccator for 1 hour, and the weight of the crucible was weighed again to measure the total weight of the crucible and the ash content. The amount of ash (that is, the amount of filler) and the total amount of organic matter are calculated by the following formulas.
-Filler amount [%] (that is, ash content [%])
= (Total weight of crucible and sample after combustion / cooling [g] -Weight of crucible [g]) / (Total weight of crucible and sample before combustion [g] -Weight of crucible [g]) x 100
-Total amount of organic matter [%] = 100-ash content [%]
The above measurement was carried out at n = 2, and the average value was taken as the reported value.
In addition, the bulk density, average foam diameter, number of coarse particles, and standard deviation of the foamed sheet were measured. The measurement results are shown in Tables 1 to 4.
In addition, the strength and flexibility of the obtained foamed sheet were evaluated as follows. The evaluation results are shown in Tables 1 to 4.

<Number of fillers Average particle size, standard deviation (σ)>
The foamed sheet was cross-sectioned with an ion milling device, and the cross-section was observed by SEM.
The obtained cross-sectional SEM photograph (magnification of 10,000 times) uses the software of Image-Pro Premier (manufactured by media) to binarize the white component and polylactic acid component corresponding to the filler, and the range is 10 μm × 7 μm. The particle diameter (ferred diameter) was determined in 1 and the number average particle diameter and standard deviation (σ) were calculated for the white component (filler) having a ferret diameter of 0.005 μm or more.

<Degree of hydrophobization>
1 g of the filler was weighed and suspended on the surface of 50 mL of pure water. Methanol was added dropwise while stirring this, and the amount of methanol (mass%) required to suspend the entire amount of the filler in pure water was determined.

<pH>
A suspension of 4% effervescent nucleating agent (water / methanol = 1: 1 vol / vol) was prepared using the filler. The pH of this prepared suspension was measured using a pH meter (manufactured by DKK-TOA CORPORATION).

<Number of coarse filler particles>
50 mg of the foamed sheet 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.

<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%. Next, the weight (g) of this foamed sheet was precisely weighed. The bulk density was determined by dividing the weight of the foam sheet by the bulk volume.

<Average foam diameter>
The obtained foam sheet was cross-sectioned with an ion milling apparatus, and the cross-section was observed by SEM.
The obtained cross-sectional SEM photograph (magnification of 3,000 times) was obtained by binarizing the gray component and the resin component (white) corresponding to foaming (voids) using software of Image-Pro Premier (manufactured by media). The average particle diameter (ferred diameter) was determined in the range of 35 μm × 20 μm, and the average foamed diameter was calculated for the gray component (foaming) having a ferret diameter of 0.5 μm or more.
The average foam diameter is the value for the above three foams.

<Strength>
The tensile strength of the obtained foamed sheet is measured in accordance with JIS K6767, and the following evaluation criteria are used based on how strong the non-foamed sheet (polylactic acid sheet) is. The strength was evaluated based on. The measurement result of the non-foamed sheet was 55 MPa.
-Evaluation criteria-
〇 Tensile strength of 60% or more for non-foamed sheet △ Tensile strength of 40% or more and less than 60% for non-foamed sheet × Tensile strength of less than 40% for non-foamed sheet Strength

The symbols of the aliphatic polyester resin in the table indicate the following.
PLA (a): Polylactic acid (REVODE110, manufactured by HISUN, melting point 160 ° C)
PLA (b): Polylactic acid (Revode190, manufactured by HISUN, melting point 175 ° C.)
PLA (c): Polylactic acid (Revode101, manufactured by HISUN, melting point 150 ° C.)
PBS: Polybutylene succinate PGA: Polyglycolic acid (PGA)

Examples of aspects of the present invention are as follows.
<1> Containing an aliphatic polyester resin and a filler,
The degree of hydrophobization of the filler is 50% by mass or more, and the degree of hydrophobization is 50% by mass or more.
The foamed sheet is characterized in that the pH of the filler is 6.5 or less.
<2> The foamed sheet according to <1>, wherein the number average particle diameter of the filler is 5 nm to 100 nm.
<3> The foamed sheet according to any one of <1> to <2>, wherein the pH of the filler is 3.5 or more and 6.5 or less.
<4> The foamed sheet according to any one of <1> to <4>, wherein the number of coarse particles of the filler having a particle size of 10 μm or more is 100 particles / mm ^{2 or less.}
<5> The foamed sheet according to any one of <1> to <4>, wherein the content ratio of the aliphatic polyester resin is 80% by mass or more with respect to the total amount of organic substances in the foamed sheet.
<6> The foamed sheet according to any one of <1> to <5>, wherein the bulk density is 0.9 g / cm ^{3 or less.}
<7> The foamed sheet according to any one of <1> to <6>, wherein the filler is silica.
<8> The foamed sheet according to <7>, wherein the content ratio of the silica is 50% by mass or more with respect to the total amount of the inorganic substances in the foamed sheet.
<9> The foamed sheet according to any one of <1> to <8>, wherein the aliphatic polyester resin is at least one selected from polylactic acid, polybutylene succinate, and polyglycolic acid.
<10> A product comprising the foamed sheet according to any one of <1> to <9>.
<11> The product according to <10>, which is at least one selected from bags, packaging containers, tableware, cutlery, stationery, and cushioning materials.
<12> An kneading step of kneading the aliphatic polyester resin and the filler at a temperature lower than the melting point of the aliphatic polyester resin in the presence of a compressible fluid to obtain an aliphatic polyester resin composition.
A foaming step of foaming the aliphatic polyester resin composition when the compressible fluid is removed from the aliphatic polyester resin composition, and a foaming step of foaming the aliphatic polyester resin composition.
A method for producing an effervescent sheet, which comprises.
<13> The method for producing an effervescent sheet according to <12>, wherein the effervescent sheet is the effervescent sheet according to any one of <1> to <9>.
<14> The method for producing an effervescent sheet according to any one of <12> to <13>, wherein the compressible fluid is carbon dioxide.
<15> A method for producing a product obtained by molding the foam sheet according to any one of <1> to <9> by at least one of vacuum forming, compressed air forming, and press molding.

The foam sheet according to any one of <1> to <9>, the product according to any one of <10> to <11>, and the foam sheet according to any one of <12> to <14>. According to the production method of the above-mentioned product and the production method of the product according to <15> above, various problems in the prior art can be solved and the object of the present invention can be achieved.

1 Resin pellet supply tank 2 Calcium carbonate supply tank 3 Compressible fluid supply tank 4 T-die 100 Continuous kneading device

JP-A-2007-46019 Japanese Patent No. 5207277 Japanese Patent No. 5454137 Japanese Unexamined Patent Publication No. 2006-328225

Claims (11)

Contains aliphatic polyester resin and filler,
The degree of hydrophobization of the filler is 50% by mass or more, and the degree of hydrophobization is 50% by mass or more.
An effervescent sheet characterized in that the pH of the filler is 6.5 or less. The foamed sheet according to claim 1, wherein the number average particle diameter of the filler is 5 nm to 100 nm. The foamed sheet according to any one of claims 1 to 2, wherein the pH of the filler is 3.5 or more and 6.5 or less. The foamed sheet according to any one of claims 1 to 3, wherein the content ratio of the aliphatic polyester resin is 80% 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 4, wherein the filler is silica. The foamed sheet according to claim 5, wherein the content ratio of silica is 50% by mass or more with respect to the total amount of inorganic substances in the foamed sheet. A product comprising the foamed sheet according to any one of claims 1 to 6. The product according to claim 7, which is at least one selected from bags, packaging containers, tableware, cutlery, stationery, and cushioning materials. In the presence of a compressible fluid, an aliphatic polyester resin and a filler are kneaded at a temperature lower than the melting point of the aliphatic polyester resin to obtain an aliphatic polyester resin composition.
A foaming step of foaming the aliphatic polyester resin composition when the compressible fluid is removed from the aliphatic polyester resin composition, and a foaming step of foaming the aliphatic polyester resin composition.
A method for producing an effervescent sheet, which comprises. The method for producing an effervescent sheet according to claim 9, wherein the effervescent sheet is the effervescent sheet according to any one of claims 1 to 6. The method for producing an effervescent sheet according to any one of claims 9 and 10, wherein the compressible fluid is carbon dioxide.

Images