JP2021134348A - Foam, foam sheet, product, and method for producing foam sheet - Google Patents

Abstract

To provide a foam having good appearance of a surface while being excellent in strength and flexibility.SOLUTION: A foam contains a polylactic resin and inorganic particles, in which a content of the polylactic resin is 95 mass% or more, a content of the inorganic particles is 0.01 mass% or more and 5 mass% or less, and a thickness with ISO whiteness of 90% or more is 500 μm or less. An average foam diameter is preferably 0.01 μm or more and 15 μm or less, and a bulk density is more preferably 0.02 g/cm3 or more and 0.9 g/cm3 or less.SELECTED DRAWING: None

Description

The present invention relates to foams, foam sheets, products, and methods for producing foam sheets.

In recent years, the problem of global warming due to an increase in the concentration of carbon dioxide in the atmosphere has become a global problem, and various industrial fields are also developing technologies for reducing carbon dioxide emissions into the atmosphere. Among them, in the field of plastic products, carbon dioxide generated when plastics manufactured from general-purpose petroleum-derived raw materials are incinerated after use is released into the atmosphere, which causes an increase in carbon dioxide in the atmosphere. The problem is that it is part of it.

Therefore, in recent years, due to the concept of carbon neutrality, plant-derived raw materials and plastics have been attracting attention. Among the plant-derived raw materials, the characteristics of polylactic acid, which is biodegradable and is a plant-derived raw material, have been attracting attention in recent years.
In order to widely use polylactic acid, a foamed sheet in which the amount of polylactic acid is reduced by foaming the polylactic acid has been proposed (see, for example, Patent Documents 1 to 4). Further, it is widely practiced to process the polylactic acid once into a sheet shape so that the polylactic acid can be easily processed into various shapes such as bags, containers, and trays depending on the intended use. However, there are few proposals for the foamed sheet obtained by foaming the polylactic acid.

An object of the present invention is to provide a foam having a good surface appearance while being excellent in strength and flexibility.

The foam of the present invention as a means for solving the above-mentioned problems contains a polylactic acid resin and inorganic particles, and contains polylactic acid resin and inorganic particles.
The content of the polylactic acid resin is 95% by mass or more, and the content is 95% by mass or more.
The content of the inorganic particles is 0.01% by mass or more and 5% by mass or less.
The foam has a thickness of 500 μm or less so that the ISO whiteness of the foam is 90% or more.

According to the present invention, it is possible to provide a foam having a good surface appearance while being excellent in strength and flexibility.

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 foam of the present invention. FIG. 4 is a schematic view showing an example of a continuous foaming apparatus used for producing the foam of the present invention.

(Foam)
The foam of the present invention contains polylactic acid (hereinafter, also referred to as "polylactic acid resin") and inorganic particles, 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 polylactic acid sheets by mixing polylactic acid with other resins. 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.
It is known that the viscosity of an aliphatic polyester resin typified by polylactic acid drops sharply when the temperature is close to the melting point, and foam rupture and foaming coalescence are likely to occur, resulting in finer foam diameter and finer foam diameter. Uniformization is difficult in the first place.

Since plastics are used for various purposes, those having a high whiteness tend to be preferred.
In order to increase the whiteness of plastics, it has been proposed to add inorganic substances (inorganic particles) to the resin to improve the whiteness of plastics. In general, the higher the content of inorganic substances, the higher the whiteness of the plastic. However, from the viewpoint of environmental recycling mentioned above, since inorganic substances become unnecessary substances at the time of material recycling, it is preferable to reduce the content of inorganic substances as much as possible. It is known that when an inorganic substance is contained in a resin, the strength of the resin is improved due to the influence of the inorganic substance, but the flexibility of the resin is lowered (hard but brittle, and the impact resistance is low). It is also known that swirl marks, avatar-like irregularities, bubble-breaking shapes, etc. are observed on the surface appearance due to the influence of inorganic substances.

The inventors have studied in order to obtain a foam that can solve the above-mentioned problems, contains a large amount of a material having a low environmental load, and has both strength and flexibility.
If the content of the inorganic particles is 5% by mass or less with respect to the total resin, it is considered that there is no significant influence on recycling. Then, the inventors have stated that the whiteness of the foam is sufficient in this content range, that the inorganic particles in the foam are in a highly dispersed state and the bubbles of the foam are sufficiently large. We found that the bubbles were uniform. If the bubbles of the foam are sufficiently large and the bubbles are uniform, the foam has excellent strength and flexibility.
Then, the inventors have found that the strength and flexibility of the foam and the ISO whiteness, which is the state of existence of the inorganic particles in the foam, are correlated. That is, it has been found that the ISO whiteness of the foam can be used as a characteristic value for the strength and flexibility of the foam.
From the above, the content of polylactic acid is 95% by mass or more of the whole foam, the content of inorganic particles is 0.01% by mass to 5% by mass, and the ISO white color of the obtained foam. When the thickness at which the degree is 90% or more is 500 μm or less, it has been found that the foam is an excellent foam as described above, and the present invention has been completed.

<Polylactic acid resin>
Since polylactic acid resin (hereinafter sometimes referred to as "polylactic acid") is biodegraded by microorganisms, it is attracting attention as an environment-friendly low environmental load polymer material ("Structure, physical properties, rawness of aliphatic polyester". Degradable polymer 2001 Vol. 50, No. 6, p374-377 ”).
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 foaming molding temperature, 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.

The content ratio of the polylactic acid resin is 95% by mass or more, preferably 98% by mass or more, more preferably 99% by mass, based on the total amount of the foam, from the viewpoint of biodegradability and recyclability (easy recycling). preferable. If the content ratio of the polylactic acid resin is less than 95%, there may be a problem that other components remain even after the polylactic acid resin is biodegraded.

<Measuring method of polylactic acid content>
The content ratio of polylactic acid can be calculated from the ratio of the materials to be charged. If the material ratio is unknown, for example, the following GCMS (gas chromatography-mass spectrometry) analysis can be performed, and the components can be identified by comparison using known polylactic acid as a standard sample. If necessary, it is possible to calculate the area ratio of the spectrum by NMR (nuclear magnetic resonance) 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)

<Inorganic particles>
The inorganic particles are contained in order to adjust the size and amount of bubbles in the foam.
The inorganic particles may also serve as a foam nucleating material. Inorganic particles that act as the foamed core material may be referred to as a filler.
Examples of the inorganic particles include talc, kaolin, calcium carbonate, titanium oxide, layered silicate, zinc carbonate, wallastonite, silica, alumina, magnesium 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.
Among these, silica is preferable because it has a high affinity with the compressible fluid described later.

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 hexamethyldisilazane, vinyltrimethoxysilane, and γ-glycidoxypropyltrimethoxysilane. , Γ-Methyloxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane and the like.

The silica content is preferably 50% by mass or more, more preferably 60% by mass or more, based on the total amount of the inorganic particles.
The silica content is preferably 100% by mass or less.
When the silica content is 50% by mass or more, the foaming becomes uniform and fine.

The number average particle diameter of the inorganic particles is preferably 5 nm (0.005 μm) or more and 100 nm (0.1 μm) or less, and more preferably 10 nm (0.01 μm) or more and 100 nm (0.1 μm) or less. When the number average particle diameter is 5 nm or more, the dispersibility of the inorganic particles is excellent, the number of interfaces between the inorganic particles and the polylactic acid is increased, and the sheet physical properties such as the impact strength of the obtained foam are improved. Further, when the number average particle diameter is 100 nm or less, a uniform and sufficiently large foam diameter can be formed.

For convenience, the average particle size of the inorganic particles may be expressed by the BET specific surface area assuming that the foamed core material is a true sphere. Its BET specific surface area in becomes ^{20m 2} / ^g~5000m 2 / g.

The number average particle size of the inorganic particles is determined by observing the inorganic particles (filler) in the foam with a TEM (transmission electron microscope) at a magnification of 50,000 times to obtain the average particle size (number average particle size). Can be done. The number of particles used in the calculation is 100.

The content of the inorganic particles can be appropriately selected depending on the intended purpose as long as the physical properties of the foamed sheet are not impaired, but is 0.01% by mass to 5% by mass with respect to the entire foam, and is 0. 1% by mass to 5% by mass is preferable, and 0.2% by mass to 3% by mass is more preferable. If the content of the inorganic particles is less than 0.01% by mass, foaming is not sufficient, and if it exceeds 5% by mass, the inorganic particles may aggregate with each other.

The content of the inorganic particles can be calculated from the prescribed amount at the time of producing the foam, but it can also be analyzed by the inorganic elemental analysis method (O, N, H) (EA: Electronic analysis).
For example, a foam is put into a graphite crucible together with a flux and melted and decomposed by resistance heating of an impulse furnace in a helium stream, oxygen is detected as carbon dioxide and hydrogen is detected as water by an infrared detector, and nitrogen is thermally conducted as it is. It can be detected and quantified with a degree detector.

<Other ingredients>
The other components are not particularly limited as long as they are usually contained in the foam, 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 or vinyl groups is preferable.
Specific examples of these compounds include glycidyl methacrylate, glycidyl acrylate, glycerol dimethacrylate, trimethylolpropantrimethacrylate, trimethylolpropanetriacrylate, aryloxypolyethylene glycol monoacrylate, aryloxypolyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, and the like. 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 foam 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 the other components is preferably 2% by mass or less, more preferably 1% by mass or less, based on the total amount of the foam, from the viewpoint of recyclability.

<Physical characteristics of foam>
The thickness at which the ISO whiteness of the foam of the present invention is 90% or more is 500 μm or less, preferably 300 μm or less.
The fact that the thickness at which the ISO whiteness is 90% or more is 500 μm or less means that the thin film also exhibits sufficient whiteness. Further, in the foam, it means that the inorganic particles are in a highly dispersed state and that a sufficient bubble size and an existing state (dispersed state) are formed, so that both flexibility and strength of the foam can be achieved. It means that
When the thickness at which the ISO whiteness is 90% or more exceeds 500 μm, it means that there is not sufficient ISO whiteness, that is, the size and presence of bubbles are not uniform, and the flexibility of the foam. And strength may not be achieved at the same time.

Here, the mechanism by which the state of bubbles in the foam can be characterized by ISO whiteness will be considered. The general whiteness is called hunter whiteness, and the L, a, and b values are obtained using, for example, a spectroscopic color difference meter SE-2000 (manufactured by Nippon Denshoku Industries Co., Ltd.) as shown below, and JIS is used. It is known that the whiteness is obtained by using the following formula according to the L1015C method.
Whiteness (%) = 100-[(100-L) ² + a ² + b ² ] ^1/2
Hunter whiteness only measures the reflectance of light incident from one direction (45 °), and if the surface is not smooth, the measured value is affected by that surface and characterizes the condition inside the foam. It is known to be unfavorable because it is not quantified.
On the other hand, ISO whiteness can be characterized by the state of diffuse reflection by bubbles inside the foam without being affected by the surface by adopting a measuring device (diffuse reflectance meter) using an integrating sphere with a diffuse reflection surface. It is thought that it is. Therefore, the whiteness in the present invention is defined by the ISO whiteness.
Specifically, the ISO whiteness is measured with a spectroscopic whiteness meter / color difference meter (PF-10R, manufactured by Nippon Denshoku Industries Co., Ltd.). The operation method was evaluated in accordance with JIS P8148: 2001 "Measurement method of paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance)" according to the handling work manual issued by the manufacturing company.

Specifically, the method for measuring the thickness at which the ISO whiteness is 90% or more is as follows. First, two types (A and B) of sheets having different thickness levels are prepared by changing the manufacturing conditions (die thickness, extrusion speed, etc.), and the ISO whiteness is evaluated.
When either A or B of the measured sheet obtains a result of 90% or more whiteness, the film thickness at which the whiteness becomes 90% is calculated by linear approximation of the two points in the relationship between the film thickness and the whiteness. (The thicker the film thickness, the higher the whiteness).
If both A and B of the measured sheet have a whiteness of 90% or less, or 90% or more, extrapolate by linear approximation of the two points in the relationship between the film thickness and the whiteness, and obtain a film thickness of around 90%. Predict and prepare a film thickness sample of about 90%, and calculate the film thickness at which the whiteness becomes 90% in the same manner as described above.

The average foam diameter of the foam of the present invention is preferably 0.01 μm or more and 15 μm or less, and more preferably 0.1 μm or more and 8 μm or less. When the average foam diameter is 0.01 μm or more, the foam is not too small and the foam has excellent flexibility. When the average foam diameter is 15 μm or less, the foam is not too large and the foam has excellent strength.

The method for measuring the average foam diameter of the foam is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the foam 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 is preferably 0.02 g / cm ³ or more 0.9 g / cm ³ or less, more preferably 0.02 g / cm ³ or more 0.7 g / cm ³ or less, 0.02 g / cm ³ or more More preferably 0.5 g / cm ³ or less.
When the bulk density is 0.02 g / cm ³ or more, the foam can maintain sufficient strength. When the bulk density is 0.9 g / cm ³ or less, the foam has excellent flexibility, and has flexible and rigid properties.

As a method for measuring the bulk density of the foam, for example, it can be measured according to JIS K 7365.

The foam of the present invention may be used, for example, as a foam sheet or a product described later, or may be used by printing the foam as it is, or may be used in a process of processing with a mold to obtain a product. You may.

(Effervescent sheet)
The foamed sheet of the present invention contains the foam of the present invention, 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.

The average thickness of the foamed sheet is preferably 0.001 mm or more and 4 mm or less, and more preferably 0.001 mm or more and 1 mm or less. When the average thickness is 4 mm or less, the moldability is good.
Since the foamed sheet of the present invention is in a fine and uniform foamed state, the thickness of the sheet can be reduced.

Of the lengths in the extrusion direction (MD direction) and the width direction (TD direction) of the foamed sheet, the ratio (long side / long side / The thickness) is preferably 250 or more, and more preferably 2500 or more.
When the ratio (long side / thickness) is 250 or more, it is easy to process as a sheet.

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.

The foamed sheet of the present invention may have at least one of a laminated layer, a coated layer, and a surface-deposited layer on at least one of the front surface and the back surface of the foamed sheet.
Known methods can be used for laminating, coating, and surface deposition.
Examples of the shape of the multi-layer body obtained by subjecting the foamed sheet to the above-mentioned processing include a sheet shape and a bottle shape. Further, in the present invention, a sheet-shaped multi-layer body may be molded to obtain a multi-layer molded product.

As a method for producing a multi-layered body having a sheet-like shape, for example, (1) a foamed sheet (A) is prepared in advance, and a resin (B) extruded onto the sheet by a general melt extrusion machine is used. Multi-layering method (extrusion laminating method), (2) Prepare two extruders, extrude polylactic acid-based resin (C) from one to make a sheet, and simultaneously push the resin (B) from the other. An extruding method (coextrusion method) and the like can be mentioned.

(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 daily necessities. The concept of this product includes not only a single product but also a part consisting of a product such as a tray handle and a product having a product such as a tray to which a handle is 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.
Examples of the packaging container include a food container, an agricultural / gardening container, a blister pack container, a press-through pack container, various bag making containers, a fluid container, and the like. Specific examples of food containers include fresh food trays, instant food containers, fast food containers, lunch boxes, and the like. Specific examples of agricultural / horticultural containers include seedling raising pots. In addition to food, specific examples of blister pack containers include packaging containers for various product groups such as office supplies, toys, and dry batteries. Specific examples of fluid containers include beverage cups and beverage bottles for dairy products, soft drinks and alcoholic beverages, temporary storage containers for seasonings such as soy sauce, sauces, mayonnaise, ketchup and cooking oil, shampoo and rinse. Such as containers, cosmetic containers, pesticide containers, and the like.

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, for example, industrial materials, daily necessities, agricultural products, food products, pharmaceutical products, cosmetic sheets, packaging materials, trays, etc. It can be widely applied as an application.

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)
The method for producing a foam of the present invention includes a kneading step and a foaming step, and further has other steps if necessary.
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 polylactic acid resin and the inorganic particles at a temperature lower than the melting point of the polylactic acid resin in the presence of a compressible fluid.
In the kneading step, a foaming agent may be added in addition to the polylactic acid resin and the inorganic particles in order to promote foaming more efficiently.
The polylactic acid resin and the kneaded product of inorganic particles may be referred to as a polylactic acid resin 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 inorganic particles tend to agglomerate when the inorganic particles (filler) or the like are kneaded. The effect is remarkable when the size of the inorganic particles is small.
In the present invention, in order to uniformly disperse the inorganic particles in this polylactic acid, kneading is performed using a compressible fluid. When the compressible fluid is the same as the foaming agent, the inorganic particle 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 inorganic particles and the polylactic acid 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 kneading of inorganic particles (fillers), pressure may be applied without using a compressible fluid, but this reduces the free volume of the resin and increases the interaction between the resins (increased viscosity). This is intended and 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 inorganic particles are dispersed in the resin in such a state, the inorganic particles are dispersed in the liquid, and the inorganic particles aggregate 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 inorganic particles 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 a compressible fluid can be used for kneading the polylactic acid resin and the inorganic particles, the present inventors have made a poly It was found that the viscosity of the lactic acid resin became suitable for kneading, and the inorganic particles could be kneaded. In particular, the polylactic acid 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, inorganic particles 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 polylactic acid 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 is present 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 amount of carbon dioxide supplied is 30% by mass or less, it is possible to prevent a problem that carbon dioxide and polylactic acid are phase-separated and a foam having a uniform thickness cannot be obtained.

<< Kneading device >>
As the kneading device used for producing the polylactic acid resin composition, a continuous process or a batch process can be adopted, but it is appropriate in consideration of the device efficiency, product characteristics, quality, etc. , It is preferable to select the reaction process.
As a kneading device, a single-screw extruder, a twin-screw extruder, a kneader, a non-screw 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 apparatus 100 uses a twin-screw extruder (manufactured by JSW) (screw diameter 42 mm, L / D = 48, apparatus 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 as inorganic particles (the same applies hereinafter) 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 device, but these set values can be said to be 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 from the polylactic acid resin composition to foam the polylactic acid resin 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.

Specifically, the foaming step can be carried out as follows.
A tandem type in which a second extruder (L / D: 34, diameter: 65 mm) is connected to the tip of a twin-screw extruder (manufactured by JSW) (screw diameter 42 mm, L / D = 48) via a connecting pipe. An extruder was used.
Next, carbon dioxide is press-fitted as a compressed fluid from the middle of the first extruder, and polylactic acid (filler masterbatch) in which molten inorganic particles are dispersed and carbon dioxide as a compressed fluid are uniformly kneaded and then suitable for foaming. It was cooled to the resin temperature.
Then, the molten resin composition is obtained from a circular mold having a slit diameter of 70 mm attached to the tip of the second extruder under the conditions of a constant discharge amount (for example, 5 to 30 kg / h) and a constant resin temperature (for example, 100 to 200 ° C.). An object is extruded and foamed, and a tubular polylactic resin foam sheet extruded from a mold slit is placed along a cooled mandrel, and the outer surface is cooled and molded by blowing air from an air ring to foam. The body is obtained.

In the foaming step, the compressible fluid dissolved in the polylactic acid composition vaporizes and precipitates at the interface between the inorganic particles and the polylactic acid resin in response to operations such as depressurization and heating to change the solubility of the compressed fluid. This causes foaming. Since the foaming starts from the inorganic particles as the foaming core material, the foam having uniform and fine foaming can be produced only when the inorganic particles are 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.

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

The fillers used are as follows.
1) Filler (A)
HMDS (Hexamethyldisilazane) Hydrophobized Silica 2) Filler (B) with an average particle size of 30 nm
Dimethyldichlorosilane hydrophobized silica with an average particle size of 15 nm 3) Filler (C)
HMDS (Hexamethyldisilazane) Hydrophobized Silica 4) Filler (D) with an average particle size of 120 nm
Ultra-fine powdered heavy calcium carbonate with an average particle size of 700 nm (ACE-35, manufactured by Calfine Co., Ltd.)
5) Filler (E)
Heavy calcium carbonate (KS-500, manufactured by Calfine Co., Ltd.), which is a general product with an average particle size of 4400 nm.

The polylactic acid resin used is as follows.
1) Polylactic acid resin (A)
Revode110, manufactured by HISUN, melting point 160 ° C
2) Polylactic acid resin (B)
Revode190, manufactured by HISUN, melting point 175 ° C
3) Polylactic acid resin (C)
Revode101, manufactured by HISUN, melting point 150 ° C
4) Polylactic acid resin (D)
Revode290, manufactured by HISUN, melting point 180 ° C

(Example 1)
<Manufacturing of filler masterbatch>
Using the continuous kneading apparatus 100 shown in FIG. 3, the polylactic acid (A) and the filler (A) as inorganic particles were supplied so as to have a total flow rate of 10 kg / hr. Polylactic acid (A) is 9.7 kg / hr, filler (A) is 0.3 kg / hr, carbon dioxide is supplied as a compressible fluid of 0.99 kg / h (equivalent to 10% by mass of polylactic acid), and kneading is performed. Was carried out to obtain a filler master batch pellet (A).
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 filler masterbatch (polylactic acid resin composition) containing 3% by mass of a filler was obtained.

<Manufacturing of foam and foam sheet>
Using the continuous foam sheet forming apparatus 100 shown in FIG. 4, the 3 mass% filler masterbatch (A) and the polylactic acid resin (A) were supplied so as to have a total flow rate of 10 kg / hr. Polylactic acid resin (A) 8.33 kg / hr, 3 mass% filler masterbatch 1.67 kg / hr, carbon dioxide as a compressible fluid 0.99 kg / hr so that the filler is 0.5% by mass. h (corresponding to 10% by mass with respect to polylactic acid resin) was supplied, kneaded, and the obtained kneaded product was subjected to a second extruder.
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 polylactic acid resin temperature of 167 ° C., and the obtained kneaded product is extruded and foamed from the mold slit. The tubular polylactic acid resin foam sheet was placed along the cooled mandrel, and the outer surface thereof was cooled and molded by blowing air from an air ring to obtain a foam. The obtained foam was incised with a cutter to obtain a flat sheet-like foam sheet.
The temperature of each zone is 1st extruder: raw material mixing / melting area a and compressible fluid supply area b: 190 ° C., kneading area c: 150 ° C., 2nd 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.

(Example 2)
In Example 1, the foam and foam sheet of Example 2 were obtained in the same manner as in Example 1 except that the content of the filler in the foam was set to 3% by mass.

(Example 3)
In Example 1, the foaming of Example 3 was carried out in the same manner as in Example 1 except that the filler (A) was changed to the filler (B) and the content of the filler in the foam was 0.1% by mass. Body and foam sheets were obtained.

(Example 4)
In Example 1, the foam and the foam of Example 4 were obtained in the same manner as in Example 1 except that the filler (A) was changed to the filler (C) and the content of the filler in the foam was 5% by mass. A foam sheet was obtained.

(Example 5)
In Example 1, the foam and foam sheet of Example 5 were obtained in the same manner as in Example 1 except that the content of the filler in the foam was 0.02% by mass.

(Example 6)
In Example 1, the foam and foam sheet of Example 6 were obtained in the same manner as in Example 1 except that the polylactic acid resin (A) was changed to the polylactic acid resin (B).

(Example 7)
In Example 1, the foam and the foam of Example 7 were obtained in the same manner as in Example 1 except that the filler (A) was changed to the filler (D) and the content of the filler in the foam was 5% by mass. A foam sheet was obtained.

(Example 8)
In Example 1, the filler and the polylactic acid resin were put into the apparatus of FIG. 4 without producing the filler masterbatch to obtain the foam and foam sheet of Example 8.
Specifically, it was manufactured as follows.
Using the continuous foam sheet forming apparatus 100 shown in FIG. 4, the filler (A) and the polylactic acid resin (A) were supplied so as to have a total flow rate of 10 kg / hr. The ratio of polylactic acid resin (A) is 9.5 kg / hr and filler (A) is 0.5 kg / hr so that the filler is 0.5% by mass, and carbon dioxide is 0.99 kg / h (as a compressible fluid). (Equivalent to 10% by mass of polylactic acid resin) was supplied, kneaded, and the obtained kneaded product was subjected to a second extruder.
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 polylactic acid resin temperature of 167 ° C., and the obtained kneaded product is extruded and foamed from the mold slit. The tubular polylactic acid resin foam sheet was placed along the cooled mandrel, and the outer surface thereof was cooled and molded by blowing air from an air ring to obtain a foam. The obtained foam was incised with a cutter to obtain a flat sheet-like foam sheet.
The temperature of each zone is 1st extruder: raw material mixing / melting area a and compressible fluid supply area b: 190 ° C., kneading area c: 150 ° C., 2nd 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.

(Example 9)
In Example 1, the foam and foam sheet of Example 9 were obtained in the same manner as in Example 1 except that the content of the filler in the foam was 0.01% by mass.

(Example 10)
In Example 1, the foaming of Example 10 was carried out in the same manner as in Example 1 except that the filler (A) was changed to the filler (B) and the content of the filler in the foam was 0.015% by mass. Body and foam sheets were obtained.

(Example 11)
In Example 1, the foam and foam sheet of Example 11 were obtained in the same manner as in Example 1 except that the polylactic acid resin (A) was changed to the polylactic acid resin (C).

(Example 12)
In Example 1, the foam and foam sheet of Example 12 were obtained in the same manner as in Example 1 except that the polylactic acid resin (A) was changed to the polylactic acid resin (D).

(Comparative Example 1)
In Example 1, the foam and foam sheet of Comparative Example 1 were obtained in the same manner as in Example 1 except that the filler was not used.

(Comparative Example 2)
In Example 1, the foam and foam sheet of Comparative Example 2 were obtained in the same manner as in Example 1 except that the content of the filler in the foam was 6% by mass.

(Comparative Example 3)
In Example 1, the foam and the foam of Comparative Example 3 were obtained in the same manner as in Example 1 except that the filler (A) was changed to the filler (E) and the content of the filler in the foam was 7% by mass. A foam sheet was obtained.

(Comparative Example 4)
In Example 1, the foam and foam sheet of Comparative Example 4 were obtained in the same manner as in Example 1 except that kneading was performed without using a compressed fluid when the filler masterbatch 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: 190 ° C., compressible fluid removal area d: 190 ° C., and molding processing area e: 190 ° C.

The average foam diameter, bulk density, thickness when the ISO whiteness was 90% or more, and the thickness of the foam sheet of the obtained foam were measured as follows. The measurement results are shown in Table 1.

<Average foam diameter of foam>
The foam sheet was cross-sectioned with an ion milling device, and the cross-section was observed by SEM (scanning electron microscope). 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 (ferret diameter) was determined in the range of 35 μm × 20 μm, and the average foam diameter of the foam was calculated for the gray component (foam) having a fillet diameter of 0.5 μm or more.
The measurement was performed at 100 points, and the average thereof was taken as the average foam diameter.

<Bulk density>
Bulk density was measured according to JIS K 7365.

<Thickness when ISO whiteness is 90% or more>
The measurement was performed using a spectroscopic whiteness meter / color difference meter (PF-10R, manufactured by Nippon Denshoku Industries Co., Ltd.). The specific operation method was in accordance with the manufacturer's handling manual, and the measurement was in accordance with JIS P8148: 2001 "Measurement method for paper, paperboard and pulp-ISO whiteness (diffuse blue light reflectance)".

<Thickness of foam sheet>
The thickness of the foamed sheet is an average value obtained by measuring the thickness at five locations using a high-precision digital micrometer (MDH-25MB, manufactured by Mitutoyo Co., Ltd.).

The strength (flexural modulus), flexibility (tensile impact strength), and surface appearance of the obtained foam were measured and evaluated as follows. The evaluation results are shown in Table 2.

<Strength (flexural modulus)>
The flexural modulus was measured according to JIS K 7171 and evaluated based on the following evaluation criteria. The flexural modulus was analyzed by the tangential method (initial tangential gradient of the stress-strain curve).
The larger the value of the flexural modulus, the higher the flexural modulus and the higher the strength.
-Evaluation criteria-
◎ 2,100 MPa or more 〇 1,400 MPa or more and less than 2,100 MPa △ 1,200 MPa or more and less than 1,400 MPa × 1,200 MPa or less

<Flexibility (tensile impact strength)>
The tensile impact strength was measured according to the JIS K 7160 A method and evaluated based on the following evaluation criteria. The larger the value, the higher the impact resistance, and the more than Δ is the level that can be actually used.
-Evaluation criteria-
◎ 27kJ / ^{m 2} or more 〇 21kJ / ^{m 2} or more 27kJ / ^m less than ² △ 13 kJ / ^{m 2} or more and less than 21kJ / ^{m 2} × 13kJ / ^m less than ²

<Surface appearance>
The presence or absence of avatar-like unevenness and bubble rupture shape in a sheet having a 100 mm square area was visually observed and evaluated based on the following evaluation criteria.
-Evaluation criteria-
〇Avatar-like unevenness and bubble-breaking shape, etc. are 0 or more and less than 5 △ Abata-like unevenness and bubble-breaking shape, etc. are 6 or more and less than 10 pieces that's all

Examples of aspects of the present invention are as follows.
<1> Contains polylactic acid resin and inorganic particles,
The content of the polylactic acid resin is 95% by mass or more, and the content is 95% by mass or more.
A foam having a content of the inorganic particles of 0.01% by mass or more and 5% by mass or less.
The foam is characterized in that the thickness at which the ISO whiteness of the foam is 90% or more is 500 μm or less.
<2> The foam according to <1>, wherein the average foam diameter is 0.01 μm or more and 15 μm or less.
<3> The foam according to any one of <1> to <2>, wherein the bulk density is 0.02 g / cm ³ or more and 0.9 g / cm ^{3 or less.}
<4> The foam according to any one of <1> to <3>, wherein the number average particle diameter of the inorganic particles is 5 nm or more and 100 nm or less.
<5> The inorganic particles contain silica and
The foam according to any one of <1> to <4>, wherein the content ratio of silica is 50% by mass or more with respect to the total amount of the inorganic particles.
<6> A foamed sheet containing the foam according to any one of <1> to <5>.
<7> The foamed sheet according to <6>, wherein the average thickness is 0.001 mm or more and 4 mm or less.
<8> The foamed sheet according to any one of <6> to <7>, which has at least one of a laminated layer, a coated layer, and a surface-deposited layer on at least one of the front surface and the back surface.
<9> The product comprises the foamed sheet according to any one of <6> to <8>.
<10> The product according to <9>, which is at least one selected from bags, packaging containers, tableware, cutlery, stationery, and daily necessities.
<11> A kneading step of kneading the polylactic acid resin and the inorganic particles in the presence of a compressible fluid at a temperature lower than the melting point of the polylactic acid resin to obtain a polylactic acid resin composition.
A foaming step of foaming the polylactic acid resin composition when the compressible fluid is removed from the polylactic acid resin composition, and a foaming step of foaming the polylactic acid resin composition.
It is a method for producing an effervescent body, which is characterized by having.
<12> The method for producing an foam according to <11>, wherein the compressible fluid is carbon dioxide.

The foam according to any one of <1> to <5>, the foam sheet according to any of <6> to <8>, the product according to any one of <9> to <10>, the above < According to the method for producing a foam according to any one of 11> to <12>, 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 Filler 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. 2009-073955

Claims (11)

Contains polylactic acid resin and inorganic particles,
The content of the polylactic acid resin is 95% by mass or more, and the content is 95% by mass or more.
A foam having a content of the inorganic particles of 0.01% by mass or more and 5% by mass or less.
A foam having a thickness of 500 μm or less so that the ISO whiteness of the foam is 90% or more. The foam according to claim 1, wherein the average foam diameter is 0.01 μm or more and 15 μm or less. The foam according to any one of claims 1 to 2, wherein the bulk density is 0.02 g / cm ³ or more and 0.9 g / cm ^{3 or less.} The foam according to any one of claims 1 to 3, wherein the number average particle diameter of the inorganic particles is 5 nm or more and 100 nm or less. The inorganic particles contain silica and
The foam according to any one of claims 1 to 4, wherein the content ratio of silica is 50% by mass or more with respect to the total amount of the inorganic particles. A foamed sheet containing the foam according to any one of claims 1 to 5. The foamed sheet according to claim 6, wherein the average thickness is 0.001 mm or more and 4 mm or less. The foamed sheet according to any one of claims 6 to 7, which has at least one of a laminated layer, a coated layer, and a surface-deposited layer on at least one of the front surface and the back surface. A product comprising the foamed sheet according to any one of claims 6 to 8. The product according to claim 9, which is at least one selected from bags, packaging containers, tableware, cutlery, stationery, and daily necessities. A kneading step in which a polylactic acid resin and inorganic particles are kneaded at a temperature lower than the melting point of the polylactic acid resin in the presence of a compressible fluid to obtain a polylactic acid resin composition.
A foaming step of foaming the polylactic acid resin composition when the compressible fluid is removed from the polylactic acid resin composition, and a foaming step of foaming the polylactic acid resin composition.
A method for producing a foam, which comprises.

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