JP6200746B2 - Acrylic resin foam and manufacturing method thereof - Google Patents

Description

  The present invention relates to an acrylic resin foam and a method for producing the same.

Conventionally, acrylic resin foams (hereinafter also referred to as “foams”) are excellent in strength, light weight, and heat insulation, so that fiber-reinforced plastics (FRP) containing resin (carbon fiber) Laminated reinforced plastic (CFRP, etc.) is used to construct automobile bodies, hulls for small boats, freight car wall compartments, wind power blades, X-ray transmission tables, etc. It is used as a member for
Such an acrylic resin foam is usually produced by preparing a polymerizable solution in which urea as a foaming agent and a radical polymerization initiator are mixed with an acrylic monomer, as shown in Patent Document 1 below. After pouring a polymerizable solution into a mold and heating the mold together to polymerize the acrylic monomer, the obtained foamable polymer is further heated to a high temperature in a mold to decompose urea. It is produced by adopting a method of gas foaming. Moreover, in the method of patent document 1, the thing containing maleic anhydride and methacrylamide is used as an acrylic monomer from a viewpoint that high heat resistance can be provided to the acrylic resin foam obtained. .

JP 2006-045256 A

However, an acrylic resin foam in which maleic anhydride and methacrylamide are contained in the polymer structural unit has a problem that it is difficult to become high in apparent density and excellent in lightness while having high heat resistance.
On the other hand, Patent Document 1 discloses a method of adding a chain transfer agent to a polymerizable monomer containing maleic anhydride and methacrylamide in order to obtain a foam having excellent lightness.
However, when a chain transfer agent is added to a polymerizable monomer containing maleic anhydride and methacrylamide, the time until the polymerization of the polymerizable monomer is completed is prolonged as compared with the case where no chain transfer agent is added. There is a problem of end.
For such problems, conventionally, it has been effective to produce an acrylic resin foam excellent in heat resistance and light weight while preventing a prolonged time until the polymerization of the polymerizable monomer is completed. No method has been found, and it is difficult to improve the production efficiency of the acrylic resin foam excellent in heat resistance and light weight.

By the way, when producing a fiber reinforced composite in which the core material is an acrylic resin foam and the surface material is an FRP sheet, the FRP sheet is laminated on the surface of the acrylic resin foam, Adhesion between an acrylic resin foam and an FRP sheet is performed by heating under pressure.
Here, the knowledge that the air etc. in the resin contained in the FRP sheet adversely affects the mechanical strength and the like of the finally obtained fiber reinforced composite has been obtained. As a countermeasure against this, a technique of increasing the temperature together with the pressure at the time of bonding the acrylic resin foam and the FRP sheet is implemented.
However, when heated at a high temperature, there is a problem that the acrylic resin foam used as the core material is thermally contracted.
Furthermore, the thermal contraction of the acrylic resin foam is not limited to the case of manufacturing a fiber reinforced composite, but may be a problem even when the acrylic resin foam is used alone.

  In view of the above problems, the present invention is to provide an acrylic resin foam that is excellent in heat resistance and light weight, can prevent the prolongation of manufacturing time, and further hardly undergoes volume change due to heating. A method for producing an acrylic resin foam that can produce an acrylic resin foam that is excellent in heat resistance and light weight and hardly changes in volume due to heating while preventing prolongation of the production time. This is a second task.

In order to solve the above-mentioned problems, the present inventors have intensively studied and contain an acrylic resin and a plasticizer, and the structural unit of the acrylic resin polymer contains maleic anhydride and methacrylamide. The acrylic resin foam has been found to be excellent in heat resistance and light weight, and can prevent the production time from being prolonged, and has led to the completion of the present invention.
In addition, the present inventors have intensively studied to solve the above problems, and an acrylic resin foam having an average cell diameter of 0.7 mm or less and an open cell ratio of 15% or less is heated. As a result, it was found that the volume change due to is difficult to occur, and the present invention has been completed.

That is, the present invention contains an acrylic resin and a plasticizer,
The acrylic resin contains maleic anhydride and methacrylamide as structural units,
An acrylic resin foam having an average cell diameter of 0.7 mm or less and an open cell ratio of 15% or less.

The present invention also includes an acrylic monomer, a polymerizable monomer containing at least maleic anhydride and methacrylamide as the acrylic monomer, a foaming agent containing a thermally decomposable foaming agent, a polymerization initiator, and a plasticizer. And a step of producing an acrylic resin foam by foaming the foamable polymer obtained by the polymerization after polymerizing the polymerizable monomer.
In the method for producing an acrylic resin foam, the acrylic resin foam having an average cell diameter of 0.7 mm or less and an open cell ratio of 15% or less is prepared.

  According to the present invention, it is possible to provide an acrylic resin foam that is excellent in heat resistance and light weight, can prevent prolongation of the production time, and is less susceptible to volume change due to heating. It is possible to provide a method for producing an acrylic resin foam that can produce an acrylic resin foam that is excellent in heat resistance and light weight and hardly changes in volume due to heating, while preventing an increase in time.

  Embodiments of the present invention will be described below.

First, the manufacturing method of the acrylic resin foam of this embodiment is demonstrated.
The manufacturing method of the acrylic resin foam of this embodiment includes a polymerizable solution containing a polymerizable monomer containing an acrylic monomer, a foaming agent containing a pyrolytic foaming agent, a polymerization initiator, and a plasticizer. Make it.
Next, the polymerizable monomer is polymerized by heating the polymerizable solution to produce a foamable polymer (hereinafter also referred to as a foamable polymer production step). The foamable polymer is foamed to produce an acrylic resin foam (hereinafter also referred to as “foam”) having an average cell diameter of 0.7 mm or less and an open cell ratio of 15% or less. (Hereinafter also referred to as a foam production step).
Hereinafter, the components of the polymerizable solution will be described.

(Acrylic monomer)
As the acrylic monomer, an acrylic monomer containing at least maleic anhydride and methacrylamide is used. By containing maleic anhydride and methacrylamide, high heat resistance can be imparted to the resulting acrylic resin foam.
In addition, when urea is used as a foaming agent to be described later, the acrylic monomer preferably contains a water-soluble acrylic monomer because it exhibits excellent solubility in urea, and contains (meth) acrylic acid. It is preferable to make it.
In this specification, the term “(meth) acryl” means either “methacryl” or “acryl”.
The acrylic monomer preferably contains methyl methacrylate in that it can exhibit excellent foamability when foaming the foamable polymer of the acrylic monomer.
As acrylic monomers other than maleic anhydride, methacrylamide, (meth) acrylic acid, and methyl methacrylate, maleic acid, fumaric acid, itaconic acid, itaconic anhydride, crotonic acid, methyl acrylate, (meth) acrylic Ethyl acid, butyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, acrylamide, maleic acid amide, maleic acid imide, etc. May be included.

(Polymerizable monomer other than acrylic monomer)
In addition, as a polymerizable monomer other than the acrylic monomer, a monomer copolymerizable with the acrylic monomer may be contained in a small amount in the polymerizable solution for the purpose of modifying the acrylic resin foam.
In particular, it is preferable to contain a styrene monomer effective for improving foamability in the polymerizable solution.
However, since an excessive amount of styrene monomer may impair the hardness, the content of the styrene monomer in the polymerizable monomer is preferably 20% by mass or less.

More specifically, in the polymerizable solution in the present embodiment, 35 to 60% by mass of the polymerizable monomer contained is methyl methacrylate, 14 to 35% by mass is (meth) acrylic acid, It is preferable that 20% by mass is styrene, 1.0 to 10% by mass is maleic anhydride, and 1.0 to 10% by mass is methacrylamide. This is because if the amount of maleic anhydride and methacrylamide is small, the effect of improving the heat resistance is small, and if the amount is large, the foamability of the foamable polymer is lowered and it may be difficult to obtain a good foam. In particular, by adopting such a blend, a foamable polymer excellent in foamability can be obtained, and an acrylic resin foam excellent in heat resistance, hard and excellent in strength can be obtained.
In addition, all (meth) acrylic acid contained in the ratio of 14-35 mass% may be methacrylic acid, all may be acrylic acid, and both methacrylic acid and acrylic acid are combined. You may make it contain in a polymeric solution so that it may become the mass%.
However, when urea is used as a foaming agent to be described later, it is preferable to contain a large amount of methacrylic acid from the viewpoint of solubility in urea.

(Foaming agent)
As the foaming agent, a foaming agent containing a pyrolytic foaming agent is used.
The pyrolyzable foaming agent decomposes at 65 ° C. or higher to generate gas, and preferably decomposes at 100 to 180 ° C. to generate gas.
Examples of the pyrolytic foaming agent include urea, urea derivatives, dinitrosopentamethylenetetramine, amidoguanidine, trimethylenetriamine, paratoluenesulfone hydrazine, azodicarbonamide, thiourea, ammonium chloride, dicyandiamide, dioxane, hexane, and water Examples include chloral and citric acid. In particular, urea is a suitable blowing agent.
When the content of the pyrolytic foaming agent is small, the foaming degree of the resulting acrylic resin foam may be reduced and the lightness may be impaired. There is a risk that it is difficult to uniformly dissolve the decomposable foaming agent, the thermal decomposable foaming agent tends to remain in the resulting acrylic resin foam, or foam breakage occurs.
Therefore, the pyrolytic foaming agent is preferably contained in the polymerizable solution at a ratio of 0.5 to 30 parts by mass when the total amount of polymerizable monomers is 100 parts by mass. When the mold blowing agent is urea, it is preferable that the polymerizable solution contains 1 to 15 parts by mass when the total amount of the polymerizable monomers is 100 parts by mass.
As other foaming agents other than the pyrolytic foaming agent, a physical foaming agent (alcohol etc.) having a boiling point of 65 ° C. or higher can be used, and a physical foaming agent (alcohol etc.) having a boiling point of 65 ° C. to 180 ° C. is preferred. . Specific examples include alcohols such as isopropanol, cyclopentanol, ethanol, 1-propanol, 2-methyl-2-propanol, and 2-ethyl-1-hexanol. A physical foaming agent is not effective even when used alone, and is effective when used in combination with a pyrolytic foaming agent. As a usage-amount, when making the total amount of a polymerizable monomer into 100 mass parts, it is preferable to make it contain in a polymerizable solution in the ratio which will be 0.6-30 mass parts with the total amount with a thermal decomposition type foaming agent. .

(Polymerization initiator)
As the polymerization initiator, a redox polymerization initiator, a thermal decomposition initiator, a photodecomposition initiator, or the like is used. The higher the decomposition temperature, the more difficult it is to adjust the polymerization rate of the polymerizable solution, but from the viewpoint of easy adjustment of the polymerization rate of the polymerizable solution, it is possible to use a redox polymerization initiator, for example, t-butyl hydroperoxide. preferable.
Specific substances that can be used as redox polymerization initiators other than the t-butyl hydroperoxide include cumene hydroxy peroxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3. , 3-tetramethylbutyl hydroperoxide and the like.
The polymerization initiator is preferably contained in the polymerizable solution at a ratio of 0.1 to 5 parts by mass when the total amount of polymerizable monomers is 100 parts by mass.

(Plasticizer)
Examples of the plasticizer include phthalic acid ester, adipic acid ester, trimellitic acid ester, polyester, phosphoric acid ester, citric acid ester, epoxidized vegetable oil, sebacic acid ester, azelaic acid ester, maleic acid ester, benzoic acid ester, sulfone. An acid ester or the like is used.
Examples of the phthalic acid ester include dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, and dibutyl phthalate. Examples of the adipic acid ester include dioctyl adipate, diisononyl adipate, diisobutyl adipate, dibutyl adipate, and the like. Examples of the trimellitic acid ester include trioctyl trimellitic acid. Examples of the phosphate ester include tricresyl phosphate, triamyl phosphate, and tributyl phosphate. Examples of the citric acid ester include acetyl tributyl citrate, triethyl citrate, and triethyl acetyl citrate. Examples of the epoxidized vegetable oil include epoxidized soybean oil and epoxidized linseed oil. Examples of the sulfonic acid esters include alkyl sulfonic acid phenyl esters, and examples of commercially available sulfonic acid esters include Mesamol from LANXESS.
As the plasticizer, dioctyl phthalate, diisobutyl adipate, tributyl acetylcitrate, sulfonate, and the like are preferably used.
If the amount of the plasticizer is small, the foamability of the foamable polymer may be insufficient. If the amount is large, the rigidity of the obtained acrylic resin foam may be reduced, or the bubbles of the acrylic resin foam may be coarsened. Or the acrylic resin foam may shrink at the time of foaming. When the total amount of the polymerizable monomer is 100 parts by mass, it is contained in the polymerizable solution in a ratio of 0.1 to 20 parts by mass. It is preferable that 0.3-10 mass parts is more preferable, and 0.5-5 mass parts is especially preferable.

(Calcium ion)
In the present embodiment, the polymerizable solution can further contain calcium ions.
As the substance for adding calcium ions, calcium salts such as calcium formate, calcium acetate, calcium silicate and calcium nitrate can be used, and at least one of calcium formate, calcium acetate and calcium silicate is preferably used.
From the viewpoint that it is easy to produce an acrylic resin foam that hardly undergoes a volume change due to heating, in the polymerizable solution, the total amount of the substance for adding calcium ions is 2.4 with respect to 100 mol parts of the polymerizable monomer. It is preferable that it is * 10 ^{< -3} > -2.4 * 10 ^<-2 > mol part.

(Anhydrous sodium sulfate)
In the present embodiment, the polymerizable solution may further contain anhydrous sodium sulfate.
From the viewpoint that it is easy to produce an acrylic resin foam that hardly undergoes a volume change due to heating, in the polymerizable solution, the anhydrous sodium sulfate is 8.0 × 10 ⁻⁴ to 100 parts by mass of the polymerizable monomer. The amount is preferably 1.2 × 10 ⁻² parts by mass.

(Reducing agent)
Furthermore, in the present embodiment, the polymerizable solution can further contain a reducing agent.
As the reducing agent, a compound capable of reducing (donating electrons) other compounds such as a nitrogen-containing compound such as N, N-dimethylaniline can be used.
Specific examples of nitrogen-containing compounds other than N, N-dimethylaniline that can be used as a reducing agent include amine compounds such as triethylamine.
The reducing agent is preferably contained in the polymerizable solution in a weight ratio of 0.1 to 5 times the content of the polymerization initiator.

(Metal ions, chloride ions)
In the present embodiment, the polymerizable solution includes one or more metal ions selected from the group consisting of Cu ⁺ , Cu ²⁺ , Fe ³⁺ , Ag ⁺ , Pt ²⁺ , and Au ^3+. Further, chloride ions can be further contained.
Each of the metal ions has a positive oxidation-reduction potential.
In addition, the metal ion exhibits a function as an electron-donating substance, that is, an oxidizing agent, or an electron-donating substance, that is, a reducing agent, in a polymerizable solution, and a polymerization reaction of the polymerizable monomer. It contributes to promotion.
On the other hand, the chloride ion contributes to the promotion of the polymerization reaction of the polymerizable monomer by binding or desorption from the metal ion.

The above metal ions and chloride ions may be contained in the polymerizable solution at the same time in the form of copper chloride, ferric chloride, silver chloride, gold chloride, and may be polymerized by separate substances. You may make it contain in a solution.
In addition to the above chlorides, for example, the above-described metal ions may be contained in the polymerizable solution by a substance such as copper bromide, copper iodide, copper stearate, copper naphthenate, or silver bromide. it can.
In addition, about copper, silver, and gold | metal | money, the ion can be contained in a polymeric solution not by the above salts but by the metal itself or an alloy.
For example, copper, copper alloy (constantan: copper / nickel alloy, brass: copper / zinc alloy), silver, gold fine particles, wires, mesh, etc. are mixed in the polymerizable solution to polymerize these ions. Can be contained.

  Examples of specific substances for containing chloride ions in the polymerizable solution include 1,3-dimethylimidazolium chloride, 1-butyl-3-methylimidazolium in addition to sodium chloride and hydrochloric acid, for example. Chloride, 1-butyl-2,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-methyl-3-n-octylimidazolium chloride, 1-methyl-1-hydroxyethyl-2- Tallow alkyl-imidazolium chloride and other imidazolium salt type surfactants, hexatrimethylammonium chloride, dodecylyltrimethylammonium chloride, stearyltrimethylammonium chloride, coconut alkyltrimethylammonium chloride, beef tallow alkyltrimethy Ammonium chloride, behenyl trimethyl ammonium chloride, poly diallyl dimethyl ammonium chloride, dialkyl dimethyl ammonium chloride, cetyl trimethyl ammonium chloride, and the like quaternary ammonium salt type surfactants such as lauryl trimethyl ammonium chloride.

In addition, as a specific substance for containing the chloride ion in the polymerizable solution, any one of sodium chloride, hydrochloric acid, hexatrimethylammonium chloride, dialkyldimethylammonium chloride, cetyltrimethylammonium chloride, and lauryltrimethylammonium chloride. In particular, it is preferable to employ cetyltrimethylammonium chloride.
In the case where these chloride ion-containing substances are contained in the polymerizable solution, usually, in a ratio of 0.005 to 5 parts by mass when the total amount of the polymerizable monomers in the polymerizable solution is 100 parts by mass. It can be included.

In addition, specific materials for containing the metal ions in the polymerizable solution include silver chloride, copper chloride, copper stearate, copper naphthenate, ferric chloride, or copper (copper particles and copper wire). Is preferred.
When these are contained in the polymerizable solution, the ratio is usually 1 × 10 ⁻¹⁰ to 1 × 10 ⁻² parts by mass when the total amount of the polymerizable monomers in the polymerizable solution is 100 parts by mass. It can be included. In particular, from the viewpoint of polymerization control, when the total amount of polymerizable monomers in the polymerizable solution is 100 parts by mass, it is preferably contained in a proportion of 1 × 10 ⁻¹⁰ to 1 × 10 ⁻² parts by mass.

(Acrylic resin foam)
In the present embodiment, the polymerizable solution may further contain an acrylic resin foam obtained by foaming a foamable polymer of a polymerizable monomer that is the same as or different from the polymerizable monomer.
The acrylic resin foam contributes to the acceleration of the polymerization reaction of the polymerizable monomer in the polymerizable solution.
The acrylic resin foam is preferably 0.1 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more when the total amount of polymerizable monomers in the polymerizable solution is 100 parts by mass. Preferably it is contained in the polymerizable solution at a ratio of 5 to 10 parts by mass.
In the polymerizable solution, when the acrylic resin foam is 20 parts by mass or less with respect to 100 parts by mass of the total amount of polymerizable monomers, the acrylic resin foam is uniformly dissolved in the polymerizable monomer. It has the advantage of being easy. In addition, the polymerizable solution is such that the acrylic resin foam is 0.1 parts by mass or more with respect to 100 parts by mass of the total amount of polymerizable monomers, so that the polymerizable monomer in the polymerizable solution is polymerized. Has the advantage of being promoted.

(Foaming polymer production process)
In the foaming polymer preparation step, the polymerizable monomer in the polymerizable solution is polymerized by heating the polymerizable solution at a temperature equal to or higher than the temperature at which the polymerizable monomer is polymerized and lower than the temperature at which the foaming agent is decomposed. This is a step of producing a foamable polymer.
The temperature for heating the polymerizable solution is preferably a temperature lower than the decomposition temperature of the foaming agent to be used (the temperature of the foaming agent having the lowest decomposition temperature when plural kinds of foaming agents are used). A temperature that is at least 10 ° C. lower than the temperature is preferred.

(Foam production process)
The foam preparation step is a step of heating the foamable polymer at a temperature equal to or higher than the temperature at which the foaming agent decomposes to decompose the foaming agent to form an acrylic resin foam.
The temperature at which the foamable polymer is heated is preferably a temperature equal to or higher than the decomposition temperature of the foaming agent used (the temperature of the foaming agent having the highest decomposition temperature when a plurality of types of foaming agents are used). A temperature higher by 10 ° C. or more than the decomposition temperature is preferable. About this heating temperature, it is preferable to set it as 200 degrees C or less. By making this heating temperature 200 or less, it can suppress that an acrylic resin foam shrink | contracts with a heat | fever.

  According to the method for producing an acrylic resin foam of the present embodiment, a foaming agent comprising an acrylic monomer, a polymerizable monomer containing at least maleic anhydride and methacrylamide as the acrylic monomer, and a pyrolytic foaming agent. And a polymerization solution containing a polymerization initiator and a plasticizer, and after polymerizing the polymerizable monomer, the foamable polymer obtained by the polymerization is foamed to have an average cell diameter of 0. By producing the acrylic resin foam having a thickness of 0.7 mm or less and an open cell ratio of 15% or less, it is possible to obtain an acrylic resin foam in which volume change due to heating hardly occurs.

Next, the acrylic resin foam according to this embodiment will be described.
The acrylic resin foam according to the present embodiment contains an acrylic resin and a plasticizer. The acrylic resin contains maleic anhydride and methacrylamide as structural units.

Furthermore, it is important that the average cell diameter of the acrylic resin foam according to the present embodiment is 0.7 mm or less, and preferably 0.1 to 0.6 mm.
When the average cell diameter is 0.7 mm or less, the acrylic resin foam does not easily change in volume due to heating.
The average bubble diameter is calculated as follows.
That is, the acrylic resin foam was cut and the portion excluding the outside 1/10 in the cut surface thickness direction was enlarged 18 times using a scanning electron microscope (“S-3000N” manufactured by Hitachi, Ltd.). The cut surface is photographed and an image of the photographed cut surface is printed on A4 paper. Next, six arbitrary line segments (length 60 mm) are drawn per sheet, and the average chord length for each line segment is calculated from the number of bubbles overlapping the line segment by the following equation. However, the line segment is drawn as much as possible so that the bubbles do not come into contact with only the contacts, and if they are in contact, they are included in the number of bubbles.
Average chord length (t) = length of line segment / (number of bubbles x photo magnification)
Then, the bubble diameter D is calculated by the following formula.
D = t / 0.616
And the arithmetic average value of the bubble diameter D calculated | required for every line segment is calculated | required, and let this arithmetic average value be the average bubble diameter of an acrylic resin foam.

Moreover, it is important that the open cell ratio of the acrylic resin foam according to the present embodiment is 15% or less, and preferably 8 to 15%.
When the open cell ratio is 15% or less, the acrylic resin foam does not easily change in volume due to heating.
The open cell ratio of the acrylic resin foam can be measured by the 1-1 / 2-1 atmospheric pressure method in accordance with ASTM D-2856-87.

Furthermore, the acrylic resin foam according to the present embodiment contains calcium and sodium from the viewpoint that volume change due to heating is less likely to occur, and the concentration of calcium is 10 to 100 μg / g, and the concentration of sodium Is preferably 2 to 40 μg / g.
The concentration of calcium and sodium in the acrylic resin foam is determined by ashing the acrylic resin foam, mixing the ash and concentrated hydrochloric acid, and diluting with distilled water for ICP emission spectroscopic analysis. Can be obtained.

In addition, the acrylic resin foam according to the present embodiment preferably has a heat resistant temperature of 140 ° C. or higher, more preferably 145 to 170 ° C. in TMA (thermomechanical analysis).
In addition, the heat-resistant temperature in TMA (thermomechanical analysis) is measured as follows.
That is, a test piece was prepared by cutting a foam into a 5 mm (longitudinal) × 5 mm (horizontal) × 2 mm (thickness) rectangular parallelepiped, and using a thermomechanical analyzer, in a compression test mode (indenter tip φ3 mm in a nitrogen atmosphere) , Quartz probe), with a load of 100 mN, an indenter is applied to the test piece in the thickness direction, and the temperature is increased from 30 ° C. at a heating rate of 5 ° C./min. The thickness of the test piece becomes the thickness of the test piece before the test. On the other hand, the temperature when changed by 10% is measured, and this temperature is defined as the heat resistant temperature in TMA.
Note that correction is made by setting the quartz coefficient before analysis. The thickness of the test piece is measured by applying an indenter with a load of 100 mN to the test piece before measurement. Furthermore, as a thermomechanical analyzer, a thermal / stress / strain measuring device (trade name “EXSTRAR TMA / SS6100” manufactured by SII Nano Technology Co., Ltd.) or the like can be used. For the analysis, a soft Muse attached to the thermal / stress / strain measuring apparatus can be used.

In addition, the acrylic resin foam according to the present embodiment preferably has an apparent density of 0.15 g / cm ³ or less, more preferably 0.12 g / cm ³ or less, from the viewpoint of lightness. On the other hand, if the apparent density is too small, the mechanical strength is lowered, so that it is preferably 0.03 g / cm ³ or more, and more preferably 0.04 g / cm ³ or more.
The apparent density of the acrylic resin foam can be measured by the following method. That is, a test piece having a length of 25 mm, a width of 25 mm, and a thickness of 25 mm was cut from a sample that had passed 72 hours or more after molding of the foam so as not to change the structure of the original bubbles of the material, and the test piece was JIS K7100: 1999. After adjusting the condition for 16 hours in the second grade environment, the size and mass of the test piece are measured and calculated by the following equation. For measuring the dimensions of the test piece, “DIGIMATIC” CD-15 type manufactured by Mitutoyo Corporation is used.
Apparent density (g / cm ³ ) = 10 ³ × test piece mass (g) / test piece volume (mm ³ )

Since the acrylic resin foam according to this embodiment has a small volume change rate due to heating, it can be suitably used as a core material of a fiber-reinforced composite.
The fiber reinforced composite includes an acrylic resin foam as a core material and fiber reinforced plastics (FRP) laminated on the surface of the core material.
Examples of fiber reinforced plastics (FRP) include carbon fiber reinforced plastic (CFRP).
The fiber reinforced composite can be obtained, for example, as follows. First, a laminated body is obtained by laminating an acrylic resin foam and a fiber reinforced plastic (FRP) sheet. And under pressure of 0.1 MPa to 8 MPa, the laminate was subjected to (GRP glass transition temperature of FRP sheet (° C.)-60 ° C.) to (FRP sheet matrix resin glass transition temperature (° C.) + 80 ° C.). By heating at a temperature of 1 to 180 minutes, the acrylic resin foam and the fiber reinforced plastics (FRP) sheet are bonded. Thereby, a fiber reinforced composite can be obtained. Here, the temperature at the time of bonding the acrylic resin foam and the FRP sheet is such that the air in the resin contained in the FRP sheet can be extracted more efficiently (of the matrix resin of the FRP sheet). It is more preferable to set the temperature to (glass transition temperature -20 ° C) to (glass transition temperature of matrix resin of FRP sheet + 80 ° C).

  In addition, although the manufacturing method and acrylic resin foam of the acrylic resin foam which concern on this embodiment had the said advantage by the said structure, the manufacturing method and acrylic of the acrylic resin foam of this invention The resin-based resin foam is not limited to the above-described configuration, and can be appropriately changed in design.

  Next, the present invention will be described more specifically with reference to examples, comparative examples, reference examples, and reference comparative examples.

(Evaluation)
The example which performed various evaluation about the acrylic resin foam is shown.
First, an evaluation method for a foamable polymer and an acrylic resin foam will be described.

(Density of foamable polymer)
By cutting the foamable polymer so that cracking does not occur in the foamable polymer, a test piece of 10 cm ³ or more is obtained, the mass of the test piece is measured, and the density of the foamable polymer is calculated by the following formula: did.
Density of foamable polymer (g / cm ³ ) = mass of test piece (g) / volume of test piece (cm ³ )

(Whether or not the foamable polymer is cured)
The judgment as to whether or not the foamable polymer was cured was made as follows. That is, a plate-shaped test piece of 50 mm (length) × 50 mm (width) × 20 (thickness) was produced from the obtained foamable polymer. Next, the test piece was pressed in the thickness direction on the pressing surface of the hardness meter using an Asker rubber / plastic hardness meter C type (manufactured by Kobunshi Keiki Co., Ltd.). And when the measured value 30 seconds after pressing the test piece on the pressing surface was 80 points or more, it was judged that the foamable polymer was cured.

(Concentration of Ca (calcium) and concentration of Na (sodium) in acrylic resin foam)
The calcium concentration (Ca concentration) and the sodium concentration (Na concentration) of the acrylic resin foam were measured by the methods described above. Specifically, it measured as follows.
First, as a pretreatment, the acrylic resin foam is finely cut, about 0.5 to 2.0 g of the cut sample is placed in a crucible and precisely weighed, and the cut sample in the crucible is ashed under the following ashing conditions. The incinerated product and 2 mL of concentrated hydrochloric acid were mixed to obtain a mixed solution. Then, this mixed solution was filtered with a filter paper (Toyo Filter Paper, ADVANTEC No. 7) to remove insoluble matters. Next, the mixed solution from which insolubles had been removed was diluted with distilled water and the volume was adjusted to 50 mL to prepare a test solution for ICP measurement.
Next, the measurement solution was subjected to ICP emission spectroscopic analysis under the following ICP measurement conditions, and the Ca concentration and the Na concentration in the measurement solution were calculated from the calibration curve. When either the calcium concentration or sodium concentration in the test solution exceeded the upper limit of the calibration curve, the test solution was further diluted with distilled water so that it was within the range of the calibration curve. .
And the density | concentration of the calcium in an acrylic resin foam and the density | concentration of sodium were computed from the following formula.
Calcium concentration in acrylic resin foam (μg / g) = Calcium concentration in measurement solution (μg / mL) × 50 (mL) ÷ Sample mass (g)
Sodium concentration in acrylic resin foam (μg / g) = Sodium concentration in measurement solution (μg / mL) × 50 (mL) ÷ Sample mass (g)
<Ashing conditions>
Measuring device: Electric furnace Muffle furnace STR-15K (manufactured by Isuzu)
Ashing conditions: 450 ° C. × 3 hr (sample amount = about 0.5 to 2.0 g)
<ICP measurement conditions>
Measuring device: Multi-type ICP emission spectroscopic analyzer ICPE-9000 manufactured by Shimadzu Corporation
Measurement elements: Ca (317.933 nm), Na (5899.592 nm)
Observation direction = axial direction, high frequency output = 1.20 kW, carrier flow rate = 0.7 L / min, plasma flow rate = 10.0 L / min, auxiliary flow rate = 0.6 L / min, exposure time = 30 seconds, standard for calibration curve Liquid: US SPEX XSTC-13 (general-purpose mixed standard solution) 31 elements mixed (base 5% by mass HNO ₃ )-about 10 mg / L each
Calibration curve preparation method: The above standard curve standard solution was diluted with distilled water in stages to prepare standard solutions of 0 ppm (blank), 0.2 ppm, 1.0 ppm, 2.5 ppm and 5 ppm. The standard solution of each concentration was measured under the above conditions, and the peak intensity of the wavelength of each element was obtained. Concentration and peak intensity were plotted to obtain an approximate curve (straight line or quadratic curve) by the least square method, and this was used as a calibration curve for quantification.

(Apparent density of acrylic resin foam)
The apparent density of the acrylic resin foam was measured by the method described above.

(Open cell ratio of acrylic resin foam)
The open cell ratio of the acrylic resin foam was measured by the following method. That is, the acrylic resin foam was cut out so as not to have a molding surface skin on all six surfaces of the molded body, and the cut surface was finished with a pan slicer to produce three 25 mm × 25 mm × 25 mm cubic test pieces. . Each test piece was conditioned for 16 hours in a JIS K7100-1999 symbol 23/50, second grade environment, and then measured in a JIS K7100-1999 symbol 23/50, second grade environment. The measurement of the open cell ratio of each test piece was performed as follows. First, the outer dimension of the measurement sample was measured to 1/100 mm using a “DIGIMATIC” CD-15 type manufactured by Mitutoyo Corporation to determine the apparent volume (cm ³ ). Next, the volume (cm < ³ >) of the measurement sample was calculated | required by the 1-1 / 2-1 atmospheric pressure method using the air comparison type hydrometer 1000 type | mold (Tokyo Science Co., Ltd. product). The open cell ratio (%) was calculated from the value obtained above and the following formula, and the arithmetic average value of three tests was obtained. The air comparison hydrometer was corrected with a standard sphere (large 28.9 cc, small 8.5 cc).
Open cell ratio (%) = 100 × (apparent volume−volume measured with an air-based hydrometer) / apparent volume

(Average cell diameter of acrylic resin foam)
The average cell diameter of the acrylic resin foam was measured by the method described above.

(Volume change rate of acrylic resin foam when heated at 190 ° C. for 1 hour)
The volume change rate of the acrylic resin foam when heated at 190 ° C. for 1 hour was determined as follows. That is, first, the volume of the foam at normal temperature and normal pressure (25 ° C., 1 atm) before heating (volume before heating) was determined. And the foam from which the volume before a heating was calculated | required was heated at 190 degreeC for 1 hour using oven ("N50-S4H" by Satake Chemical Machine Industry). Next, the heated foam was cooled to room temperature. And the volume (volume after a heating) of the foam cooled to normal temperature under normal temperature normal pressure was calculated | required. Next, the volume change rate was calculated by the following formula.
Volume change rate (%) = 100 × (volume after heating−volume before heating) / volume before heating The volume of the foam was determined as follows. That is, first, water was added to the graduated cylinder, and the scale on the water surface of the graduated cylinder (first scale) was read. And the foam was put so that it might be located under the water surface of a graduated cylinder, and the scale (2nd scale) of the water surface of the graduated cylinder in that case was read. Next, the first scale was subtracted from the second scale, and this value was taken as the volume of the foam.
In addition, since the foams obtained in the examples and comparative examples were formed almost according to the mold, the volume in the mold was set to “volume before heating”.

(Heat resistance test of acrylic resin foam)
In order to investigate the heat resistance of the acrylic resin foam, the heat resistance temperature in TMA (thermomechanical analysis) of the acrylic resin foam was measured by the method described above.
As a thermomechanical analyzer, a thermal / stress / strain measuring device (trade name “EXSTRAR TMA / SS6100” manufactured by SII Nano Technology Co., Ltd.) was used.

(Reference Example 1: Preparation of polymerizable solution)
As a polymerization initiator for 100 parts by mass of a polymerizable monomer comprising 47% by mass of methyl methacrylate, 25% by mass of methacrylic acid, 16% by mass of styrene, 8.0% by mass of maleic anhydride, and 4.0% by mass of methacrylamide. T-Butyl hydroperoxide (“NO-butyl P-40R” manufactured by NOF Corporation), 0.5 parts by mass of “perbutyl H-69” manufactured by NOF Corporation, cetyltrimethylammonium chloride as a substance for adding chloride ions 0.1 parts by mass, 0.2 parts by mass of calcium formate as a polymerization inhibitor, 2.0 parts by mass of sodium sulfate as a dehydrating agent, 2.0 parts by mass of dioctyl phthalate (DOP) as a plasticizer, as a foaming agent Then, 5.0 parts by mass of urea was mixed, heated and stirred at 35 ° C., and filtered to remove residual inorganic salts to prepare a polymerizable solution.

(Reference Example 1: Production of foamable polymer and acrylic resin foam (condition 1))
1500 g of the polymerizable solution of Reference Example 1 was placed in a rectangular parallelepiped mold made of Teflon (registered trademark) having an internal method of 25 mm × 200 mm × 360 mm.
And the foaming polymer (density: 1.16 g / cm < ³ >) was obtained by heating a polymerizable solution with 43.5 degreeC for 21 hours with the formwork. At this time, it was confirmed that the foamable polymer was cured.
Thereafter, the obtained foamable polymer is cut into 25 mm × 200 mm × 150 mm, put into a mold having an internal method of 70 mm × 400 mm × 300 mm, and the foamable polymer is heated at 180 ° C. for 2 hours together with the mold. An acrylic resin foam (apparent density: 0.116 g / cm ³ ) was obtained.

(Reference Example 1: Production of foamable polymer and acrylic resin foam (condition 2))
A foamable polymer and an acrylic resin foam were produced in the same manner as in Condition 1 except that the polymerizable solution was heated together with the mold at 50 ° C. for 7 hours. It was confirmed that the foamable polymer (density: 1.16 g / cm ³ ) was cured. The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Reference Example 2: Preparation of polymerizable solution)
Except that diisobutyl adipate (DIBA) was used instead of dioctyl phthalate (DOP) as a plasticizer, and 1.7 parts by mass of diisobutyl adipate (DIBA) was mixed with 100 parts by mass of the polymerizable monomer. A polymerizable solution was prepared in the same manner as in Example 1.

(Reference Example 2: Production of foamable polymer and acrylic resin foam (condition 1))
A foamable polymer and an acrylic resin foam were produced in the same manner as in Condition 1 of Reference Example 1 except that the polymerizable solution of Reference Example 2 was used instead of the polymerizable solution of Reference Example 1. . It was confirmed that the foamable polymer (density: 1.16 g / cm ³ ) was cured. The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Reference Example 2: Production of foamable polymer and acrylic resin foam (condition 2))
A foamable polymer and an acrylic resin foam were produced in the same manner as in Condition 2 of Reference Example 1 except that the polymerizable solution of Reference Example 2 was used instead of the polymerizable solution of Reference Example 1. . It was confirmed that the foamable polymer (density: 1.16 g / cm ³ ) was cured. The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Reference Example 3: Preparation of polymerizable solution)
Aside from using dibutyl acetyl citrate (ATBC) instead of dioctyl phthalate (DOP) as a plasticizer and mixing 2.1 parts by mass of tributyl acetyl citrate (ATBC) with 100 parts by mass of the polymerizable monomer. A polymerizable solution was prepared in the same manner as in Reference Example 1.

(Reference Example 3: Production of foamable polymer and acrylic resin foam (condition 1))
A foamable polymer and an acrylic resin foam were produced in the same manner as in Condition 1 of Reference Example 1 except that the polymerizable solution of Reference Example 3 was used instead of the polymerizable solution of Reference Example 1. . It was confirmed that the foamable polymer (density: 1.16 g / cm ³ ) was cured. The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Reference Example 3: Production of foamable polymer and acrylic resin foam (condition 2))
A foamable polymer and an acrylic resin foam were produced in the same manner as in Condition 2 of Reference Example 1 except that the polymerizable solution of Reference Example 3 was used instead of the polymerizable solution of Reference Example 1. . It was confirmed that the foamable polymer (density: 1.16 g / cm ³ ) was cured. The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Reference Comparative Example 1: Preparation of polymerizable solution)
Instead of dioctyl phthalate (DOP) as a plasticizer, α-methylstyrene dimer as a chain transfer agent was used, and 0.1 part by mass of α-methylstyrene dimer was mixed with 100 parts by mass of the polymerizable monomer. Except for the above, a polymerizable solution was prepared in the same manner as in Reference Example 1.

(Reference Comparative Example 1: Production of foamable polymer and acrylic resin foam (condition 1))
A foaming polymer was prepared in the same manner as in Condition 1 of Reference Example 1 except that the polymerizable solution of Reference Comparative Example 1 was used instead of the polymerizable solution of Reference Example 1. Did not fully polymerize, and the polymerizable solution did not fully cure.

(Reference Comparative Example 1: Production of foamable polymer and acrylic resin foam (condition 2 '))
An attempt was made to produce a foamable polymer in the same manner as in Condition 2 of Reference Example 1 except that the polymerizable solution of Reference Comparative Example 1 was used instead of the polymerizable solution of Reference Example 1. Did not fully polymerize, and the polymerizable solution did not fully cure.
Therefore, the mold was further heated at 50.0 ° C. for 2.5 hours to make a foamable polymer. However, the polymerizable monomer did not polymerize and the polymerizable solution did not cure. .

(Reference Comparative Example 1: Production of foamable polymer and acrylic resin foam (condition 3))
The polymerizable solution of Reference Comparative Example 1 was heated under condition 2 ′, and the polymerizable solution was further heated with the mold at 80.0 ° C. for 3 hours to obtain a foamable polymer (density: 1.16 g / cm ³ ). Got. It was confirmed that the foamable polymer was cured.
Thereafter, the foamable polymer obtained was cut into 25 mm × 200 mm × 150 mm, placed in a 70 mm × 400 mm × 300 mm mold, and the foamable polymer was heated with the mold at 180 ° C. for 2 hours to foam an acrylic resin. A body (apparent density: 0.116 g / cm ³ ) was obtained.

(Reference Comparative Example 2: Preparation of polymerizable solution)
A polymerizable solution was prepared in the same manner as in Reference Example 1 except that dioctyl phthalate (DOP) as a plasticizer was not added.

(Reference Comparative Example 2: Production of foamable polymer and acrylic resin foam (condition 1))
Production of foamable polymer and acrylic resin foam in the same manner as in condition 1 of Reference Example 1 except that the polymerizable solution of Reference Comparative Example 2 was used instead of the polymerizable solution of Reference Example 1. Tried. Although a foamable polymer (density: 1.16 g / cm ³ ) could be obtained, many cracks having a total length of 1 cm or more occurred in the acrylic resin foam, and a good acrylic resin foam could be obtained. could not. The apparent density of the acrylic resin foam was 0.130 g / cm ³ .

(Reference Comparative Example 2: Production of foamable polymer and acrylic resin foam (condition 2))
Production of foamable polymer and acrylic resin foam in the same manner as in condition 2 of Reference Example 1 except that the polymerizable solution of Reference Comparative Example 2 was used instead of the polymerizable solution of Reference Example 1. Tried. Although a foamable polymer (density: 1.16 g / cm ³ ) could be obtained, many cracks having a total length of 1 cm or more occurred in the acrylic resin foam, and a good foam could not be obtained. . The apparent density of the acrylic resin foam was 0.130 g / cm ³ .

  Table 1 shows the test results of the reference example and the reference comparative example.

As shown in Table 1, in the methods of Reference Examples 1 to 3, the time until the polymerizable solution was cured by heating was shorter than that of Reference Comparative Example 1 using a chain transfer agent. Moreover, the heat resistance of the obtained acrylic resin foam was somewhat high, and the foamable polymer had the same apparent density. Therefore, in the methods of Reference Examples 1 to 3, it was possible to efficiently produce an acrylic resin foam having superior heat resistance as compared to Reference Comparative Example 1.
Moreover, in the methods of Reference Examples 1 to 3, it was possible to obtain an acrylic resin foam having a good appearance and a low apparent density as compared with Reference Comparative Example 2 in which a chain transfer agent and a plasticizer were not used. .
Therefore, according to this invention, it turns out that the acrylic resin foam excellent in heat resistance and light weight compared with the former can be manufactured efficiently.

Example 1
As a polymerization initiator for 100 parts by mass of a polymerizable monomer comprising 47% by mass of methyl methacrylate, 25% by mass of methacrylic acid, 16% by mass of styrene, 8.0% by mass of maleic anhydride, and 4.0% by mass of methacrylamide. T-Butyl hydroperoxide (“NO-butyl P-40R” manufactured by NOF Corporation), 0.5 parts by mass of “perbutyl H-69” manufactured by NOF Corporation, cetyltrimethylammonium chloride as a substance for adding chloride ions 0.1 part by mass, 0.004 part by mass of calcium formate as a substance for adding calcium ions (3.0 × 10 ⁻³ mol part relative to 100 mol part of the polymerizable monomer), sodium sulfate 8.0 × 10 ⁻⁴ 1 part by mass, 1.7 parts by mass of a sulfonic acid ester (manufactured by LANXESS, “Mesamol”) as a plasticizer, Then, 5.0 parts by mass of urea was mixed and heated and stirred at 35 ° C. to prepare a polymerizable solution.
Next, 1500 g of the obtained polymerizable solution was put in a rectangular parallelepiped mold made of Teflon (registered trademark) having an internal method of 25 mm × 200 mm × 360 mm.
And the foaming polymer (density: 1.16 g / cm < ³ >) was obtained by heating a polymeric solution with a formwork at 40 degreeC for 25 hours. At this time, it was confirmed that the foamable polymer was cured.
Then, the obtained foamable polymer is cut into 116 g, put into a mold having an internal method of 100 mm × 100 mm × 100 mm, and the foamable polymer is heated at 180 ° C. for 2 hours together with the mold to foam an acrylic resin. A body (apparent density: 0.116 g / cm ³ ) was obtained.
In addition, the foamable polymer obtained was cut into 78 g, put into a mold having an internal method of 100 mm × 100 mm × 100 mm, and the foamable polymer was heated together with the mold at 180 ° C. for 2 hours to foam an acrylic resin. A body (apparent density: 0.078 g / cm ³ ) was obtained.

(Example 2)
The amount of calcium formate with respect to 100 parts by mass of the polymerizable monomer is 0.01 parts by mass (7.4 × 10 ⁻³ mol part with respect to 100 mol parts of the polymerizable monomer), and the amount of anhydrous sodium sulfate is 5.0 ×. except that the 10 ^-3 parts by weight, in the same manner as in example 1, an acrylic resin foam apparent density is 0.116 g / cm ^3, and an apparent density of 0.078 g / cm ³ acrylic -Based resin foam was obtained.

(Example 3)
The amount of calcium formate with respect to 100 parts by mass of the polymerizable monomer is 0.03 parts by mass (2.2 × 10 ⁻² mol part with respect to 100 mol parts of the polymerizable monomer), and the amount of anhydrous sodium sulfate is 5.0 ×. except that the 10 ^-3 parts by weight, in the same manner as in example 1, an acrylic resin foam apparent density is 0.116 g / cm ^3, and an apparent density of 0.078 g / cm ³ acrylic -Based resin foam was obtained.

Example 4
The amount of calcium formate with respect to 100 parts by mass of the polymerizable monomer is 0.01 parts by mass (7.4 × 10 ⁻³ mol part with respect to 100 mol parts of the polymerizable monomer), and the amount of anhydrous sodium sulfate is 1.2 ×. except that the 10 ^-2 parts by weight, in the same manner as in example 1, an acrylic resin foam apparent density is 0.116 g / cm ^3, and an apparent density of 0.078 g / cm ³ acrylic -Based resin foam was obtained.

(Example 5)
Calcium acetate is used in place of calcium formate, and the amount of calcium acetate is 1.2 × 10 ⁻² parts by mass with respect to 100 parts by mass of polymerizable monomer (7.3 × 10 ⁻³ mol based on 100 mol parts of polymerizable monomer). except for the parts) in the same manner as in example 2, an acrylic resin foam apparent density is 0.116 g / cm ^3, and an acrylic-based resin foam apparent density of 0.078 g / cm ³ Got the body.

(Example 6)
Calcium silicate is used in place of calcium formate, and the amount of calcium silicate is 9.0 × 10 ⁻³ parts by mass with respect to 100 parts by mass of polymerizable monomer (7.4 × 10 ⁻³ mol with respect to 100 mol parts of polymerizable monomer). except for the parts) in the same manner as in example 2, an acrylic resin foam apparent density is 0.116 g / cm ^3, and an acrylic-based resin foam apparent density of 0.078 g / cm ³ Got the body.

(Comparative Example 1)
Example except that the amount of calcium formate relative to 100 parts by weight of the polymerizable monomer was 2.0 × 10 ⁻³ parts by weight (1.5 × 10 ⁻³ parts by mole with respect to 100 parts by weight of the polymerizable monomer). 2 in the same manner as an apparent density of acrylic resin foam is 0.116 g / cm ^3, and, to obtain an acrylic resin foam apparent density is 0.078 g / cm ^3.

(Comparative Example 2)
Example except that the amount of calcium formate relative to 100 parts by weight of the polymerizable monomer was 5.0 × 10 ⁻² parts by weight (3.7 × 10 ⁻² parts by mole with respect to 100 parts by weight of the polymerizable monomer). 2 in the same manner as an apparent density of acrylic resin foam is 0.116 g / cm ^3, and, to obtain an acrylic resin foam apparent density is 0.078 g / cm ^3.

(Comparative Example 3)
An acrylic system having an apparent density of 0.116 g / cm ³ in the same manner as in Example 2 except that the amount of anhydrous sodium sulfate was changed to 4.0 × 10 ⁻⁴ parts by mass with respect to 100 parts by mass of the polymerizable monomer. A resin foam and an acrylic resin foam having an apparent density of 0.078 g / cm ³ were obtained.

(Comparative Example 4)
An acrylic system having an apparent density of 0.116 g / cm ³ in the same manner as in Example 2 except that the amount of anhydrous sodium sulfate was changed to 2.0 × 10 ⁻² parts by mass with respect to 100 parts by mass of the polymerizable monomer. A resin foam and an acrylic resin foam having an apparent density of 0.078 g / cm ³ were obtained.

  Table 2 shows the test results of the examples and comparative examples.

As shown in Table 2, the acrylic resin foams of Examples 1 to 6 within the scope of the present invention have an open cell ratio of 20% or more, and an average cell diameter of 0.8 mm or more. Compared to the acrylic resin foams of Examples 1 to 4, the absolute value of the volume change rate by heat was small.
Therefore, according to this invention, it turns out that the acrylic resin foam which a volume change by heating hardly arises compared with the past can be provided.

Claims (7)

Containing an acrylic resin and a plasticizer,
The acrylic resin contains maleic anhydride and methacrylamide as structural units,
The average cell diameter is at 0.7mm or less state, and are open cell ratio of 15% or less,
Furthermore, it contains calcium and sodium,
The concentration of calcium is 10-100 [mu] g / g, the concentration of the sodium 2~40μg / g Der Ru acrylic resin foam.   A polymerizable solution containing an acrylic monomer, a polymerizable monomer containing at least maleic anhydride and methacrylamide as the acrylic monomer, a foaming agent containing a pyrolytic foaming agent, a polymerization initiator, and a plasticizer 2. The acrylic resin foam according to claim 1, obtained by polymerizing the polymerizable monomer and then foaming a foamable polymer obtained by the polymerization.   The polymerizable monomer is methyl methacrylate 35 to 60% by mass, (meth) acrylic acid 14 to 35% by mass, styrene 10 to 20%, maleic anhydride 1.0 to 10% by mass, and methacrylamide 1.0 The acrylic resin foam of Claim 2 containing 10 mass%. A polymerizable solution containing an acrylic monomer, a polymerizable monomer containing at least maleic anhydride and methacrylamide as the acrylic monomer, a foaming agent containing a pyrolytic foaming agent, a polymerization initiator, and a plasticizer And after polymerizing the polymerizable monomer, the step of foaming the foamable polymer obtained by the polymerization to prepare an acrylic resin foam,
Producing the acrylic resin foam having an average cell diameter of 0.7 mm or less and an open cell ratio of 15% or less ;
The polymerizable solution further contains calcium ions and anhydrous sodium sulfate,
Wherein the polymerization solution, wherein the polymerizable monomer 100 molar parts, total amount 2.4 × ¹⁰ -3 ~2.4 × ^{10 -2} mol portion der Ru acrylic resin foam of the calcium ions added substances Body manufacturing method. The acrylic resin foam according to claim 4 , wherein in the polymerizable solution, the anhydrous sodium sulfate is 8.0 × 10 ^{−4 to} 1.2 × 10 ⁻² parts by mass with respect to 100 parts by mass of the polymerizable monomer. Body manufacturing method. A polymerizable solution containing an acrylic monomer, a polymerizable monomer containing at least maleic anhydride and methacrylamide as the acrylic monomer, a foaming agent containing a pyrolytic foaming agent, a polymerization initiator, and a plasticizer And after polymerizing the polymerizable monomer, the step of foaming the foamable polymer obtained by the polymerization to prepare an acrylic resin foam,
Producing the acrylic resin foam having an average cell diameter of 0.7 mm or less and an open cell ratio of 15% or less ;
The polymerizable solution further contains calcium ions and anhydrous sodium sulfate,
Wherein the polymerization solution, wherein the polymerizable monomer 100 parts by weight, the production method of the anhydrous sodium sulfate 8.0 × ¹⁰ -4 ~1.2 × ^{10 -2} parts by mass der Ru acrylic resin foam. The method for producing an acrylic resin foam according to any one of claims 4 to 6, wherein at least one of calcium formate, calcium acetate, and calcium silicate is used as a substance for adding calcium ions contained in the polymerizable solution. .