JP2013199532A - Resin foam molded body, and method of manufacturing resin foam molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin foam molded product which is excellent in a cushioning property while containing polyolefin resin and polylactic resin.SOLUTION: A resin foam molded product is formed by extrusion-foaming a resin composition which contains polyolefin resin (A) and polylactic resin (B) at a mass ratio (A:B) of 90:10 to 60:40 and further contains styrene elastomer (C), a disperse phase is formed by the polylactic resin (B) in a continuous phase formed by the polyolefin resin (A), and a particle size of the polylactic resin, which forms the disperse phase, is 2 μm or less.

Description

  The present invention relates to a resin foam molded article and a method for producing a resin foam molded article, and more particularly to a resin foam molded article containing a polyolefin resin and a polylactic acid resin and a method for producing the same.

  Resin foam molded products mainly composed of polyolefin resins are not only formed using relatively inexpensive materials such as polyethylene resins and polypropylene resins, but also have excellent buffering properties, heat insulation, mechanical strength, etc. Therefore, it has been widely used as packing materials such as cushioning materials, food containers such as food trays, and heat insulation containers.

  Of this type of resin foam moldings, the food trays etc. have a high recycling rate and are actively being carbon neutralized, but many of the cushioning materials are still used one-way, and further consideration for the environment is required. It has been.

By the way, in recent years, awareness of the global environment has increased, and environmental problems such as the exhaustion of petroleum resources have attracted attention. Instead of conventional general-purpose resins that use petroleum resources as raw materials, polylactic acid-based resins that use plants as raw materials Is attracting attention as an effective material for carbon neutralization.
For this reason, if the buffer material can contain a polylactic acid resin, carbon neutralization of the buffer material can be promoted, but generally the polylactic acid resin and the polyolefin resin are compatible. However, when a polylactic acid resin is contained in a buffer material containing a polyolefin resin as a main component, there is a risk of generating bumps or coarse bubbles and reducing the cushioning properties.

  For such a problem, for example, the following Patent Document 1 describes that a styrene-based elastomer is useful as a compatibilizing agent for a polyolefin-based resin and a polylactic acid-based resin. Therefore, it is difficult to say that a material having sufficient cushioning properties is obtained, and the cell size is 0.6 mm at least in Tables 3-1, 3-2 of the same document, for example. The situation has not been refined.

Table 2007/0883705

  This invention makes it a subject to solve such a problem, and makes it a subject to provide the resin foam molded product which is excellent in cushioning properties, even if it contains a polylactic acid-type resin with a polyolefin-type resin.

  As a result of intensive studies by the present inventor to solve the above problems, a resin foam molded article having excellent cushioning properties can be obtained by dispersing polylactic acid resin in a fine particle form and dispersing it in polyolefin resin. As a result, the present invention has been completed.

  That is, according to the present invention relating to a resin foam molded article for solving the above problems, the polyolefin resin (A) and the polylactic acid resin (B) are in a mass ratio (A: B) of 90:10 to 60:40. The resin composition further containing the styrene-based elastomer (C) is extruded and foamed, and in the continuous phase formed by the polyolefin-based resin (A), the polylactic acid-based resin (B) A dispersed phase is formed, and the particle size of the polylactic acid resin forming the dispersed phase is 2 μm or less.

In the present specification, “the particle size of the polylactic acid resin is 2 μm or less” means that the resin foam molded article is extruded in the production direction (MD) and the width direction (TD) perpendicular to the extrusion direction. ) And the cut sections of MD and TD are cut in the thickness direction (VD), and each cross section is observed at a magnification of about 9500 times. It means that the average particle size is all 2 μm or less in all three directions.
Further, in the present specification, the longest diameter [Dmax] in the cross-sectional shape of each polylactic acid-based resin particle is obtained, and a straight line orthogonal to the longest diameter and the polylactic acid-based resin particle at a position that is an intermediate point of the longest diameter And the average value [(Dmax + D) / 2] of the distance [D] between the intersections and the longest diameter [Dmax] is determined as the size of the polylactic acid resin particles.

  Further, in the present invention relating to the method for producing a resin foam molded article, the polyolefin resin (A) and the polylactic acid resin (B) are contained in a mass ratio (A: B) of 90:10 to 60:40, A melt-kneading step for melt-kneading a resin composition further containing a styrene-based elastomer (C), a granulation step for producing a resin pellet from the melt-kneaded kneaded product, and a resin pellet obtained by the granulation step The polylactic acid is melted and kneaded in a extruder together with a foaming agent and extruded and foamed from a die provided at the tip of the extruder, and the polylactic acid is added into the continuous phase formed by the polyolefin resin (A). The resin foam (B) has a dispersed phase formed, and a polylactic acid resin forming the dispersed phase has a particle diameter of 2 μm or less to produce a resin foam molded article.

The resin foam molded article of the present invention contains a polylactic acid resin in addition to the polyolefin resin as a main component in the resin composition used for the formation thereof, and the compatibility between the polylactic acid resin and the polyolefin resin is included. It further contains a styrene-based elastomer that can be expected to function as an agent.
In the resin foam molded article of the present invention, the polylactic acid resin is finely dispersed and contained in the polyolefin resin. Specifically, the polylactic acid resin is in the form of particles having a particle size of 2 μm or less. Thus, the dispersed phase is formed in the continuous phase formed by the polyolefin resin.
That is, in the present invention, by forming such a microstructure in the resin foam molded article, the cell foam is fine and excellent cushioning properties can be exerted on the resin foam molded article. Can be provided.

As an embodiment according to the present invention, a resin foam molded body will be described below by taking a sheet-like molded body (hereinafter also referred to as “foamed sheet”) as an example.
In the present embodiment, a resin composition containing a polyolefin resin (A), a polylactic acid resin (B), a styrene elastomer (C), and various additives (D) is used as a foaming agent (X). The foamed sheet is formed by extrusion and foaming.
As will be described later, in this embodiment, the polyolefin resin (A) and the polylactic acid resin (B) are contained in the foamed sheet at a mass ratio (A: B) of 90:10 to 60:40. It is important to make the microstructure of the foamed sheet into a predetermined state by extruding and foaming the resin composition containing the styrenic elastomer (C) together with these, which is an important requirement in this embodiment. .
Specifically, the dispersion phase is formed by the polylactic acid resin (B) in the continuous phase formed by the polyolefin resin (A), and the particles of the polylactic acid resin forming the dispersion phase It is an important requirement that the foam sheet is formed with a diameter of 2 μm or less.
First, each material for forming the foam sheet which is the resin foam molding of this invention is demonstrated.

(A) Polyolefin resin Examples of the polyolefin resin include a polyethylene resin (A1) and a polypropylene resin (A2).
In addition to these, other polyolefin resins (Ax) such as poly-4-methylpentene-1 resin, polybutene resin, and ethylene-norbornene copolymer (COC) are also used as the foam sheet forming material of this embodiment. Is possible.
These may be used alone or in combination.

(A1) Polyethylene resin As the polyethylene resin, a high-density polyethylene resin, a medium-density polyethylene resin, a low-density polyethylene resin, or the like, which is a homopolymer of ethylene, can be employed. Furthermore, 1-hexene or 1-octene A linear low-density polyethylene resin slightly containing α-olefin such as can be used as the polyethylene resin.

(A2) Polypropylene resin As the polypropylene resin, a homopolypropylene resin composed of only a propylene component, and in addition to the propylene component, ethylene or an α-olefin component having 4 to 10 carbon atoms is contained at a ratio of about 1 to 10% by mass. A random copolymer and a block copolymer are mentioned.
In addition, as a polypropylene resin, high melt tension polypropylene resin (HMSPP) in which long chain branches are formed in the molecule by performing chemical crosslinking or electron beam crosslinking so as to exhibit high melt tension is also possible. Is something.

In the present embodiment, the polyethylene resin (A1) and the polypropylene resin (A2) may be mixed and used.
Furthermore, in this embodiment, other polyolefin resin (Ax) may be mixed with the polyethylene resin (A1) and / or the polypropylene resin (A2) and contained in the foamed sheet.
However, in this embodiment, one or both of the polyethylene resin (A1) and the polypropylene resin (A2) are 90% by mass of all the polyolefin resins (A) contained in the foamed sheet. The polyethylene resin (A1) preferably accounts for 90% by mass or more of all the polyolefin resins (A).
In particular, it is preferable that 90% by mass or more of all the polyolefin-based resins (A) is constituted by one or both of a low-density polyethylene resin and a linear low-density polyethylene resin.

Most preferably, a low-density polyethylene resin is used in that it can impart high compression and bending recovery properties to the foamed sheet, and can make the foamed sheet suitable as a cushioning material.
That is, in this embodiment, it is preferable that the polyolefin resin (A) is substantially composed only of a low-density polyethylene resin, and the low-density polyethylene resin conforms to the A method of JIS K7210 (1999). The melt flow rate (hereinafter also referred to as “MFR”) measured at a test temperature of 190 ° C. and a load of 21.18 N (2.16 kgf) is preferably 0.05 to 20 g / 10 min.

The MFR of the low-density polyethylene resin is preferably within such a range. The extruder used for producing a foamed sheet by employing a low-density polyethylene resin having an MFR of 0.05 g / 10 min or more is used. This is because an excessive load can be prevented.
In addition, it is preferable to use a low density polyethylene resin having an MFR of 20 g / 10 min or less, because not only can foam breakage during extrusion foaming be prevented, but a foam sheet having a good appearance can be easily obtained, and open cell It is because it becomes easy to obtain the foam sheet excellent in the buffer property with a low rate.
For these reasons, the MFR of the low density polyethylene resin is more preferably 0.2 to 10 g / 10 min, and particularly preferably 0.5 to 5 g / 10 min.

(B) Polylactic acid-based resin As the polylactic acid-based resin used in the present embodiment, a commercially available polylactic acid-based resin can be used. Specifically, D-lactic acid and L-lactic acid are used as monomers. Copolymerize, polymerize either D-lactic acid or L-lactic acid as a monomer, or one or two or more lactides selected from the group consisting of D-lactide, L-lactide and DL-lactide. It can be obtained by ring-opening polymerization, and any of these may be a polylactic acid resin.

  And when manufacturing polylactic acid-type resin, when D body and L body are used together as a monomer, when the ratio of the smaller optical isomer of D body or L body is less than 5 mol% (monomer In which only one of the optical isomers of D-form or L-form is used), that is, the above-mentioned polylactic acid resin is an optical isomer of both D-form and L-form as constituent monomer components And the content of the lesser optical isomer of D-form or L-form is less than 5 mol%, or the optical isomer of either D-form or L-form as a constituent monomer component In the case where only the body is contained, the polylactic acid-based resin obtained has a higher crystallinity and a higher melting point. On the other hand, when the D body and the L body are used in combination as monomers, The percentage of people with less When it mol% or more, according to lesser optical isomers increases, resulting polylactic acid-based resin, crystalline decreases it.

  In the present embodiment, a polymorphism containing both D-form and L-form optical isomers as a constituent monomer component, and the content of the smaller of the D-form and L-form is less than 5 mol%. It is preferable to use a lactic acid-based resin or a polylactic acid-based resin containing only one optical isomer of either D-form or L-form as a constituent monomer component.

Furthermore, the polylactic acid-based resin obtained by polymerizing the D-form and the L-form in combination as a monomer has a ratio of the smaller optical isomer of the D-form or the L-form of less than 4 mol%. A polylactic acid resin obtained by polymerizing a certain monomer is preferred, and a polylactic acid resin obtained by polymerizing a monomer in which the proportion of the optical isomer, whichever is smaller, of D-form or L-form is less than 3 mol% A lactic acid-based resin is more preferable, and a polylactic acid-based resin obtained by polymerizing a monomer in which the ratio of the optical isomer, which is the smaller of either the D-form or the L-form, is less than 2 mol% is particularly preferred.
That is, a polylactic acid-based resin containing both optical isomers of D-form and L-form as a constituent monomer component, and the content of the smaller optical isomer of D-form or L-form is less than 4 mol%. Preferably, a polylactic acid-based resin that contains both D-form and L-form optical isomers as a constituent monomer component, and the content of the smaller of the D-form and L-form is less than 3 mol%. More preferably, a polylactic acid resin containing both D isomer and L isomer as constituent monomer components, and the content of the lesser of the D isomer and L isomer being less than 2 mol% Is more preferable.
And as for the polylactic acid-type resin which contains D body and L body as a constituent monomer component, the ratio of the optical isomer of the smaller one of D body or L body decreases, and the polylactic acid resin becomes In addition to its crystallinity, the melting point increases.

If a commercially available polylactic acid resin is employed, for example, “HV6250H”, “HV8250H”, “TP4000”, etc. manufactured by Unitika Ltd. may be mentioned.
These can be contained in the foamed sheet alone or in a mixed state.

The polylactic acid-based resin (B) is formed by processing the foamed sheet and the foamed sheet by secondary processing, because plant-derived products are on the market. In this embodiment, as described above, the mass ratio ((A) :( B) with the polyolefin resin (A) can be used. )), It is important to be used within the range of 90:10 to 60:40.
The reason why the polylactic acid-based resin (B) in the present embodiment is 10% by mass or more in total with the polyolefin-based resin (A) is to obtain an environmentally friendly resin foam molded body as described above, and the upper limit is 40% by mass is that the polyolefin resin (A) is 60% by mass or more in total with the polylactic acid resin (B), so that the flexibility derived from the polyolefin resin (A) is expanded sheet. This is to make it appear.
That is, the reason why the polyolefin-based resin (A) and the polylactic acid-based resin (B) are used in the above ratio is mainly to make the foamed sheet environmentally friendly and excellent in buffering properties.

(C) Styrene Elastomer The styrene elastomer is a component that improves the compatibility between the polyolefin resin and the polylactic acid resin. The styrene elastomer (C) is used as the polyolefin resin (A) and the polylactic acid. The interfacial tension between the polyolefin resin and the polylactic acid resin can be reduced by melting and mixing in addition to the system resin (B), and the particle size of the dispersed phase made of the polylactic acid resin can be reduced. Can do.
The styrene-based elastomer can control the particle size of the dispersed phase depending on the type and amount of the styrene-based elastomer and how it is melt-mixed with the polyolefin-based resin (A) and the polylactic acid-based resin (B). The particle size can be reduced to 2 μm or less by selection of

  The styrene-based elastomer can be contained in the foamed sheet in a ratio of usually 0.5 to 20 parts by mass per 100 parts by mass of the total amount of the polyolefin resin and the polylactic acid resin. It is preferable that the ratio with respect to a mass part shall be 0.7-15 mass parts, and it is especially preferable to be 1-10 mass parts.

In such a range, it is preferable to contain the styrene elastomer in the foamed sheet so that the polyolefin resin and the polylactic acid resin are mixed with each other by containing the styrene elastomer at a ratio of 0.5 parts by mass or more. This is because the effect of making it more reliable is exhibited.
In general, styrene elastomers are much more expensive than low density polyethylene resins.
Accordingly, the reason why the content of the styrene elastomer is 20 parts by mass or less is that it is easy to reflect the characteristics of the polyolefin resin on the foamed sheet by maintaining the polyolefin resin content in the foamed sheet at a predetermined level or more. This is because the production cost of the foamed sheet can be prevented from becoming excessive.
In order to exert such effects more remarkably, as described above, the content of the styrene-based elastomer is 0.7 to 15 with respect to 100 parts by mass of the total amount of the polyolefin-based resin and the polylactic acid-based resin. The amount is preferably set to 1 part by mass, and particularly preferably 1 to 10 parts by mass.

  Examples of the styrene elastomer include a styrene-butadiene-styrene block copolymer (SBS), and a styrene-ethylene-butylene-styrene copolymer in which a double bond portion is almost completely hydrogenated by hydrogenation to SBS. (SEBS), styrene-butadiene-butylene-styrene copolymer (SBBS), styrene-isoprene-styrene block copolymer (SIS), partially hydrogenated SBS double bond, hydrogen SIS double bond Mainly composed of at least one aromatic vinyl polymer block mainly composed of an aromatic vinyl monomer unit and a conjugated diene monomer unit, such as an added styrene-ethylene-propylene-styrene copolymer (SEPS). A non-hydrogenated block copolymer comprising at least one conjugated diene polymer block and Thereof can be used hydrides.

Among these, SBS is particularly preferable.
As commercially available styrene elastomers, “TR2250” manufactured by JSR, “Tough Tech” manufactured by Asahi Kasei Corporation, “Septon” manufactured by Kuraray Co., Ltd., etc. can be used.
These can be contained in the foamed sheet alone or in a mixed state.

(D) Additive The resin composition used for forming the foamed sheet of the present embodiment may further contain a cell nucleus forming agent for adjusting bubbles generated by the foaming agent described later during extrusion foaming. .
Examples of the cell nucleating agent include talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate. Inorganic compound particles such as potassium sulfate, barium sulfate and glass beads, fluororesin particles such as polytetrafluoroethylene, metal salts of fatty acids such as zinc stearate, or decompose at the temperature of the extruder to generate cracked gas Such a chemical foaming agent, or a mixture of acid and alkali that reacts at that temperature to generate carbon dioxide gas.
These bubble nucleating agents can be used alone or in combination as appropriate.

By using these bubble nucleating agents, the cell size of the foam sheet obtained can be controlled.
In order to obtain such an effect, the content of the cell nucleus forming agent is based on a total of 100 parts by mass of the polyolefin resin (A), the polylactic acid resin (B), and the styrene elastomer (C). And it is preferable to set in the range of 0.1-10.0 mass parts.
In addition to the bubble nucleating agent, the resin composition can also contain additives such as an antistatic agent, an antioxidant, an ultraviolet absorber, a flame retardant, and a colorant as appropriate.
The additives other than the bubble nucleating agent have a total content (total amount excluding the bubble nucleating agent) of the polyolefin resin (A), the polylactic acid resin (B), and the styrene elastomer (C ) Is preferably set in a range of 0.1 to 10.0 parts by mass with respect to 100 parts by mass in total.

(X) Foaming agent When manufacturing the foamed sheet of this embodiment, a physical foaming agent or a chemical foaming agent can be used.
Examples of the physical blowing agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; air, nitrogen, water, carbon dioxide, and argon And the like.
In addition, as the chemical foaming agent, azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, benzenesulfonylhydrazide, toluenesulfonylhydrazide, sodium hydrogen carbonate, etc., which can also be used as the cell nucleating agent, are used. Can be mentioned.
These physical foaming agents and chemical foaming agents can be mixed and used as appropriate, and the amount of the foaming agent added may be appropriately adjusted according to the expansion ratio. The polyolefin resin (A) and the polylactic acid resin Usually, 0.4-10 mass parts is preferable with respect to 100 mass parts in total of (B) and the said styrene-type elastomer (C).

For these materials, for example, everything except the foaming agent mixed at a predetermined blending ratio is melt-kneaded and granulated. Once a full compound is produced, it is supplied to an extruder and extruded and foamed. It is also possible to obtain a foamed sheet by simply supplying a dry blend of individual material pellets directly to an extruder used for extrusion foaming and melt-kneading in the extruder, followed by extrusion foaming to obtain a foamed sheet. Also good.
In addition, the foaming agent may be press-fitted in the middle of the extruder, and the kneaded material melt-kneaded after the foaming agent press-fit is adjusted to a temperature suitable for extrusion foaming and attached to the tip of the extruder. What is necessary is just to carry out extrusion foaming in a sheet form from a circular die or a flat die.

Here, in the foamed sheet in the present embodiment, a dispersed phase is formed by the polylactic acid resin in a continuous phase formed by the polyolefin resin, and the dispersed phase has a particle size of 2 μm or less. Since it is necessary to finely disperse, it is preferable to employ the full compound method rather than the dry blend method.
That is, in the manufacturing method of a foam sheet, it is preferable to perform the following processes (A) to (C).
(A) The polyolefin resin (A) and the polylactic acid resin (B) are contained in a mass ratio (A: B) of 90:10 to 60:40, and the styrene elastomer (C) is further contained. A melt-kneading step of melt-kneading the resin composition.
(B) A granulation step of producing resin pellets from the melt-kneaded kneaded product.
(C) An extrusion foaming process in which the resin pellets obtained in the granulation process are melt-kneaded in an extruder together with a foaming agent and extruded and foamed from a die provided at the tip of the extruder.

(A) Melt-kneading step The melt-kneading step can be carried out using a general melt-kneading apparatus such as a single screw extruder, a twin screw extruder, a kneader, a Banbury mixer, an open roll, etc. In order to finely disperse the resin, it is preferable to use a twin screw extruder or the like that can apply high shear stress to the melt-kneaded material inside.
For example, a polyolefin resin, a polylactic acid resin, and a styrene elastomer that have been heated and dried in advance are introduced into a tumbler mixer, a Henschel mixer, etc. so as to have a predetermined blending ratio through a weighing machine, and this is dry blended. Thereafter, a method of supplying to a hopper of a twin screw extruder and melt-kneading with the twin screw extruder can be employed.

(B) Granulation step The granulation step is a method in which the melt-kneaded product obtained in the melt-kneading step is directly formed into a pellet shape, or once formed into a string shape or a sheet shape. It is possible to employ a method of cutting resin to form resin pellets.
For example, if the melt-kneading step is carried out with a single-screw extruder or a twin-screw extruder, a strand die equipped with a rotary blade is attached to the tip of the extruder, and the melt-kneaded material is removed from the die hole of the strand die. A method (hot cut method) is adopted in which the molten kneaded material that is discharged and accumulated at the outlet of the die hole is cut with a rotating blade at regular intervals to obtain a granular material, and the granular material is cooled to obtain a resin pellet. be able to.

  Further, without providing the rotary blade, the melt-kneaded material is extruded from a strand die in a string shape, and after passing through a cooling water tank and sufficiently cooled, it is introduced into a pelletizer to form resin pellets. Also good.

Further, when the melt-kneading step is carried out with a kneader, a Banbury mixer, an open roll, etc., the obtained melt-kneaded material is made into a lump, and this is supplied to an extruder and the resin pellets are explained as described above. What is necessary is just to make it form.
Alternatively, the batch of melt-kneaded material may be thinly extended with a cooling roll to form a mixed resin sheet, and the mixed resin sheet may be applied to a pelletizer to form resin pellets.

  The resin pellets produced in this granulation step are not particularly limited in size and shape as long as there is no hindrance to the extrusion foaming step to be carried out next, usually spherical particles of about 1 to 7 mm, Cylindrical particles and rectangular plate particles can be used.

(C) Extrusion foaming process When carrying out the extrusion foaming process, everything except the resin foam obtained in the granulation process, cell nucleation agent, and other additives, excluding physical foaming agents. Are measured and blended, and this is supplied to an extruder equipped with a circular die having a predetermined shape, melted and kneaded in the extruder, and then extruded and foamed into the circular die. Can be adopted.
In addition, the physical foaming agent may be press-fitted in the middle of the extruder, and the kneaded material melt-kneaded after the foaming agent press-fit is adjusted to a temperature suitable for extrusion foaming and attached to the tip of the extruder. What is necessary is just to carry out extrusion foaming in the sheet form from the said circular die.

However, as described above, as the microstructure of the obtained resin foam molded article, the continuous phase formed by the polyolefin resin (A) and the polylactic acid resin (B) are contained in the continuous phase. It is important to form a dispersed phase formed by dispersion, and it is important that the particle size of the polylactic acid resin forming the dispersed phase is 2 μm or less.
The particle size of the polylactic acid-based resin is preferably 1.5 μm or less, and more preferably 1 μm or less.
The microstructure is preferably a structure in which the dispersed phase is dispersed at a number density of 1.0 × 10 ^{10 to} 5.0 × 10 ¹⁵ pieces / cm ³ .
The number density is more preferably 3.0 × 10 ^{10 to} 5.0 × 10 ¹⁴ pieces / cm ³ , and particularly preferably 5.0 × 10 ^{10 to} 5.0 × 10 ¹³ pieces / cm ^3. preferable.
In addition, it is preferable that the number density is within such a range. By setting the number density to 1.0 × 10 ¹⁰ pieces / cm ³ or more, excellent foamability and flexibility are imparted to the foam sheet. × is because the mechanical strength with excellent foam sheet be 10 ¹⁵ / cm ³ or less is applied.
The specific value of the number density of the dispersed phase in the foamed sheet can be confirmed by adopting the method described in Examples.

Further, the obtained foamed sheet preferably has a cell size (hereinafter also referred to as “average cell diameter”) of 20 to 500 μm.
The average bubble diameter here means a value calculated based on an average chord length measured in accordance with a test method of ASTM D2842-69, and the foam sheet has an average bubble diameter of 70 to 400 μm. More preferably, it is 80 to 350 μm.
It is preferable to have such a cell size because the cell size can be 20 μm or more so that the foamed sheet can be given strength suitable as a cushioning material or the like, and the cell size should be 500 μm or less. This is because the foamed sheet can be given a good appearance and flexibility.

Furthermore, the foam sheet obtained has an apparent density is preferably 30~150kg / m ^3, more preferably from 40~130kg / m ^3, particularly preferably 50~120kg / m ^3.
It is preferable to have such an apparent density because an apparent density of 30 kg / m ³ or more can provide the foamed sheet with a predetermined mechanical strength and an excellent cushioning property. ^This is because by setting the apparent density to ³ or less, the foamed sheet can have excellent mechanical strength while having a predetermined lightweight property.
That is, in order to give the foamed sheet with a good balance between lightness and mechanical strength, it is preferable that the apparent density of the foamed sheet is 30 to 150 kg / m ³ .

As described above, in the present embodiment, the foamed sheet is formed with a predetermined microstructure, thereby exhibiting strength superior to that of the conventional one.
During extrusion foaming, the interface between the dispersed phase (polylactic acid-based resin) and the continuous phase (polyolefin-based resin) is also likely to be the starting point of foaming. Therefore, at the time of the resin pellet obtained by the granulation step, the dispersed phase Is preferably finished to a certain degree of fineness, and the particle size of the polylactic acid resin in the resin pellet is preferably 2 μm or less, and more preferably 1.5 μm or less.
Furthermore, in this resin pellet state, it is most preferable that the particle diameter of the polylactic acid-based resin is already 1 μm or less.

Such a foamed sheet can be used as a lining material for a corrugated cardboard box that is cut into an appropriate length and is secondarily molded as required to pack home appliances.
In general, among resin foam molded articles, a route for collecting and reusing them is being established in food trays and the like used for selling foods in supermarkets and the like.
Also, among the packaging materials, cardboard boxes and the like are reused or recycled to recycled paper, but the cushioning material is still nearly disposable.
For this reason, the resin foam molded article of the present embodiment, which can be used to expand the use of plant-derived polylactic acid-based resins, is preferably used as a cushioning material that can more effectively exhibit environmental effects. I can say that.

In addition, in this embodiment, although the sheet-like thing (foamed sheet) is illustrated as a resin foaming molded object, in this invention, the shape of a resin foaming molded object is not limited to a sheet form, A rod A hollow pipe and the like can be produced in the same manner as the foam sheet.
In addition, for example, a case where a block-shaped resin foam molded body having a three-dimensional structure is manufactured by performing extrusion foaming in a mold having a hollow region corresponding to a product shape is also within the intended scope of the present invention. There is no difference from the foam sheet specifically exemplified in the present embodiment in that such a foam block is also useful as a cushioning material.

  In addition, the resin foam molding of this invention is not only used for such a buffer material use, but can be used also for a food tray, a heat retention container, etc.

  Although no further detailed description will be given here, the resin foam molding of the present invention is appropriately applied to the conventionally known matters regarding the resin foam molded body and the production method thereof within the range in which the effects of the present invention are not significantly impaired. It can be used for the manufacturing method of a body and a resin foaming molding.

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

Example 1
First, after a polylactic acid resin having a melting point of 166 ° C. (trade name “HV6250H” manufactured by Unitika Co., Ltd.) is dried with a dehumidifying dryer, this polylactic acid resin (HV6250H) and a low density polyethylene resin having a melting point of 107 ° C. The melting point is 100 parts by mass with respect to 100 parts by mass of the mixed resin in which the product name “Novatech LD400” manufactured by Nippon Polyethylene Co., Ltd. is blended at a mass ratio of 30/70 (HV6250H / Novatech LD400). A styrene elastomer at 143 ° C. (SBS: styrene / butadiene = 52/48) [manufactured by JSR, trade name “TR2250”] was mixed in a tumbler mixer at a ratio of 6.3 parts by mass.
Next, the mixture obtained by the above mixing is supplied to a twin screw extruder having a caliber of 30 mm and L / D: 42, and melt kneaded (melt kneading step (ii)), and the melt kneaded product is attached to the tip of the extruder. The strand was extruded into a strand shape from a small hole of the die, cooled in a water tank, and the strand was cut to a mass of about 10 mg and dried to obtain a resin pellet (granulation step (b)).
Furthermore, after drying the resin pellets with a dehumidifying dryer, a ratio of 1 part by mass with respect to 100 parts by mass of the mixed resin is a cell nucleus forming agent (manufactured by Dainichi Seika Kogyo Co., Ltd., baking soda master batch, trade name “PO217K” ) And an antistatic agent (manufactured by Dainichi Seika Kogyo Co., Ltd., antistatic agent master batch, trade name “ELECON SSPE220”) having a ratio of 1.5 parts by mass was mixed with a tumbler mixer.
Thereafter, the first stage of a single-screw extruder having a diameter of 40 mm and the second stage of a single-screw extruder having a diameter of 50 mm are connected to each other through a connecting pipe to obtain the first stage by mixing. The temperature of the feeding section of the extruder is maintained at 170 ° C., the temperature of the compression section of the extruder is maintained at 200 ° C., the blowing agent injection / mixing section is maintained at 220 ° C., and the measuring section and the head section are maintained at 200 ° C. Then, from the middle of the first stage extruder, butane (isobutane: normal butane (mass ratio) = 35: 65) is press-fitted so as to be 4.8 parts by mass with respect to 100 parts by mass of the mixed resin. Then, the mixture was uniformly dispersed in the melt-kneaded product.
Next, the melt-kneaded material containing the foaming agent is continuously supplied from the first stage extruder to the second stage extruder via the connecting pipe, and cooled to the resin temperature of 108 ° C. by the second stage extruder. After that, extrusion foaming was performed into the atmosphere from a circular die having a diameter of 30 mm (clearance thickness of the opening portion: 0.4 mm) attached to the tip of the second-stage extruder.
While taking out the extruded and foamed molten mixture, it is formed into a cylindrical shape by a cooling cylindrical mandrel having a diameter of 90 mm and a length of 150 mm, and a part of the cylindrical foam is formed at the end of the cylindrical mandrel. Was cut and 200 m was scraped off as a belt-like sheet.
At that time, the sheet did not tear and could be removed stably.
The obtained foamed sheet had a density of 114 kg / m ³ and a thickness of 1.3 mm.

(Example 2)
The ratio between the polylactic acid resin and the low density polyethylene resin was changed to 10/90, and a foam sheet having a density of 65 kg / m ³ and a thickness of 1.1 mm was produced in exactly the same manner as in Example 1.

(Comparative Example 1)
After drying the polylactic acid resin (HV6250H) with a dehumidifying dryer, the polylactic acid resin (HV6250H) and a low-density polyethylene resin (Novatech LD400) having a melting point of 107 ° C. in a mass ratio of 30/70 (HV6250H / Novatech) LD400) with respect to 100 parts by mass of the mixed resin, 6.3 parts by mass of styrene elastomer (SBS: “TR2250”), 1 part by mass of cell nucleating agent (PO217K), and antistatic agent (ELECON SSPE220) 1.5 parts by mass was mixed with a tumbler mixer.
Next, the mixture obtained by the mixing is supplied to the first stage extruder (caliber 40 mm) of the tandem extruder, the temperature of the supply section of the extruder is set to 170 ° C., and the temperature of the compression section of the extruder is set to 200 ° C., blowing agent injection / mixing section at 220 ° C., metering section and head section at 200 ° C., followed by butane (isobutane: normal butane (mass ratio) from the middle of the first stage extruder = 35: 65) was pressed into 4.8 parts by mass with respect to 100 parts by mass of the mixed resin and uniformly dispersed in the melt-kneaded product of the mixture.
Subsequently, the melt-kneaded material containing the foaming agent was continuously supplied from the first-stage extruder to the second-stage extruder via a connecting pipe. After the mixed resin in the molten state is cooled to a resin temperature of 108 ° C. by a second stage extruder, a circular die having a diameter of 30 mm (opening clearance thickness of 0.4 mm) attached to the tip of the second stage extruder is used. Extruded into the atmosphere.
The extruded molten mixture is foamed and taken out and formed into a cylindrical shape with a cylindrical mandrel having a diameter of 90 mm and a length of 150 mm, and a part of the cylindrical foam is cut at the end of the cylindrical mandrel. 200 m was scraped off as a belt-like sheet.
At that time, the sheet did not tear and could be removed stably.
Further, the obtained foamed sheet had a density of 164 kg / m ³ and a thickness of 0.8 mm.

(Comparative Example 2)
A foam sheet having a density of 56 kg / m ³ and a thickness of 1.3 mm is produced in the same manner as in Comparative Example 1 except that the ratio of the polylactic acid resin and the low density polyethylene resin is changed to 10/90 and the resin temperature is changed to 109 ° C. did.

(Comparative Example 3)
Extrusion foaming was performed in the same manner as in Comparative Example 1 except that no styrene elastomer was added, but the foamed state was poor and a good sample could not be obtained.

  The following evaluation was implemented about the foam sheet obtained by each Example and the comparative example.

(Compressive strength)
After the sheet-like foam obtained by the extrusion foaming method is stored in an environment of 20 to 25 ° C. for 7 days, a plurality of 25 mm × 25 mm test pieces are cut out so that the thickness of the test pieces becomes about 15 mm. Laminated.
Attach an attachment of model number A-2 to the tip of a push-pull gauge (manufactured by Imada Seisakusho, model “PSS”), and press the attachment from the top of the laminated test piece to make the total thickness of the laminate 50% (approx. 7.5 mm) was compressed with a push-pull gauge, and the load at that time was measured.
The same operation was performed three times, and the average value was taken as the compressive strength.

(Bending recovery)
Cut a test piece of length (MD) 250 mm × width (TD) 250 mm from the sheet-like foam, fold this test piece in half (125 mm), and after 10 seconds from the moment when the bending is released, the angle of the extruded foam is set. The measurement was performed, and the same operation was performed three times.
The measurement was carried out using different test pieces for the vertical and horizontal, and the average of all measured values (six) was obtained.

(TEM observation and particle size of dispersed phase)
A section was cut out from the sheet-like foam, and the section was subjected to epoxy resin embedding, and an ultrathin section (thickness 90 nm) was prepared using an ultramicrotome (Leica ULTRACUT UCT, manufactured by Leica Microsystems). Subsequently, the cross section of the ultrathin slice was photographed with a transmission electron microscope (H-7600, manufactured by Hitachi High-Technologies Corporation). Ruthenium tetroxide was used as the staining agent. Further, the dispersion state of the polylactic acid resin was measured by a TEM photograph (9500 times), and the particle size of the dispersed polylactic acid resin was measured.

(Number density of polylactic acid resin)
The number density of the polylactic acid resin was determined using a photograph with a magnification of 9500 obtained by TEM observation.
First, the area (a) on the photograph and the number of dispersed phases (b) of the polylactic acid resin per area are counted.
The number density (d) per unit volume was calculated by dividing the number of dispersed phases by the area, calculating the number density (c) per unit area, and converting it to volume.
The same operation was calculated on the basis of photographs taken from three directions of MD, TD, and VD, and the number density was obtained.
(C) = (b) / (a)
(D) = (c) ^3/2

(Apparent density of foam)
The apparent density of the foam was measured by a method based on the method described in JIS K 7222-1999.
Specifically, a test piece of 10 cm ³ or more (100 cm ³ or more in the case of semi-rigid and soft materials) is cut from the sample so as not to change the original cell structure of the sample, and its mass is measured. Calculated.
Apparent density (kg / m ³ ) = Test piece mass (g) / Test piece volume (cm ³ ) × 10 ³

(Magnification of foam)
From the density (ρs) of the mixture of polyethylene resin and polylactic acid resin and the apparent density (ρf) of the foam, the expansion ratio (E) was calculated according to the following formula.
Foaming ratio E (times) = ρs / ρf

Where ρs: density of a mixture of polyethylene resin and polylactic acid resin ρf: density of foam

(Average bubble diameter)
The average cell diameter was calculated based on the average chord length measured according to the test method of ASTM D2842-69.
Specifically, the polylactic acid resin foam sheet is cut along the extrusion direction (MD) and the width direction (TD) perpendicular to the extrusion direction, and the center of each cut surface is scanned with an electron microscope (Co., Ltd.). Hitachi S-3000N) zoomed in and changed the field of view to take two photos, printed the images on A4 paper, and three 60mm long straight lines on each image (total to MD) The average chord length (t) of the bubbles is calculated by the following formula from the average number of bubbles in each direction drawn on the straight line. The bubble diameter in each direction (MD, TD) was calculated.

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

In addition, normally, the bubble diameter was calculated by drawing a straight line parallel to MD for a cut surface cut along MD and parallel to TD for a cut surface cut along TD.
At this time, in general, the magnification in the electron microscope is adjusted so that there are 10 to 20 bubbles on the straight line, and when drawing the straight line, the straight line penetrates the bubble without making point contact as much as possible. I was careful so that.
When some of the bubbles come into point contact with a straight line, the calculation was performed by including the bubbles in the number of bubbles, and further including the bubbles at both ends of the straight line in the number of bubbles.
And the result of MD and TD was averaged and it was set as the average bubble diameter.

(Plant degree)
The plant degree (biomass degree) of the sheet-like resin foam molded article was measured by ASTM D6866.

The above evaluation results are shown in Table 1 below.

  From the above results, it can be seen that according to the present invention, a resin foam molded article excellent in cushioning properties can be obtained while using a polylactic acid resin.

Claims (5)

  A resin composition containing a polyolefin resin (A) and a polylactic acid resin (B) in a mass ratio (A: B) of 90:10 to 60:40 and further containing a styrene elastomer (C). Is formed by extrusion foaming, and a disperse phase is formed by the polylactic acid resin (B) in a continuous phase formed by the polyolefin resin (A), thereby forming the disperse phase. A resin foam molded article having a particle size of 2 μm or less.   The resin foam molded article according to claim 1, wherein at least a part of the polyolefin resin (A) is a polyethylene resin.   The resin foam molded article according to claim 1 or 2, wherein the polyolefin resin (A) is a low density polyethylene resin having a melt mass flow rate of 0.05 g / 10 min or more and 20 g / 10 min or less.   The resin foam molded article according to any one of claims 1 to 3, which is used as a buffer material.   A resin composition containing a polyolefin resin (A) and a polylactic acid resin (B) in a mass ratio (A: B) of 90:10 to 60:40 and further containing a styrene elastomer (C). A melt-kneading step for melt-kneading, a granulation step for producing resin pellets from the melt-kneaded kneaded product, a resin pellet obtained by the granulation step is melt-kneaded in an extruder together with a foaming agent, and the extruder An extrusion foaming process is performed by extruding and foaming from a die provided at the tip, and a dispersed phase is formed by the polylactic acid resin (B) in a continuous phase formed by the polyolefin resin (A) and A method for producing a resin foam molded article, comprising producing a resin foam molded article having a particle size of 2 μm or less of a polylactic acid resin forming a dispersed phase.