JP6106044B2 - Method for producing acrylic resin foam and acrylic resin foam - Google Patents

Description

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

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 plastics (CFRP, etc.) make up the body of automobiles, hulls of small boats, wall materials for cold storage rooms of cargo vehicles, wings of wind power generation, X-ray camera tables for transmitting X-rays, 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.

JP 2006-045256 A

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, an object of the present invention is to provide a method for producing an acrylic resin foam that can produce an acrylic resin foam that hardly undergoes a volume change due to heating. It is a second object to provide a difficult acrylic resin foam.

  The present inventors have intensively studied to solve the above-mentioned problems, and use of a polymerizable monomer containing an acrylic monomer and styrene and having a styrene concentration of 30% by mass or more hardly causes a volume change due to heating. The inventors have found that an acrylic resin foam can be produced, and have completed the present invention.

That is, the present invention prepares a polymerizable solution containing a polymerizable monomer containing an acrylic monomer and styrene, a pyrolytic foaming agent, and a polymerization initiator, and after polymerizing the polymerizable monomer, A foaming polymer obtained by polymerization is foamed to produce an acrylic resin foam,
It exists in the manufacturing method of an acrylic resin foam using the thing containing 30 mass% or more of styrene as said polymeric monomer.

In addition, the present invention provides a polymerizable solution containing a polymerizable monomer containing an acrylic monomer and styrene, a pyrolytic foaming agent, and a polymerization initiator, and after polymerizing the polymerizable monomer, Obtained by foaming a foamable polymer obtained by polymerization,
The polymerizable monomer is in an acrylic resin foam containing 30% by mass or more of styrene.

  ADVANTAGE OF THE INVENTION According to this invention, the acrylic resin foam which a volume change by heating hardly arises can be provided.

  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 produces a polymerizable solution containing a polymerizable monomer containing an acrylic monomer and styrene, a foaming agent containing a pyrolytic foaming agent, and a polymerization initiator. .
Next, the polymerizable monomer is polymerized by heating the polymerizable solution to produce a foamable polymer. Then, the foamable polymer is foamed to produce an acrylic resin foam (hereinafter also referred to as “foam”).
Hereinafter, the components of the polymerizable solution will be described.

(Acrylic monomer)
Examples of the acrylic monomers include maleic anhydride, methacrylamide, (meth) acrylic acid, methyl methacrylate, maleic acid, fumaric acid, itaconic acid, itaconic anhydride, crotonic acid, methyl acrylate, and ethyl (meth) acrylate. , (Butyl) (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, acrylamide, maleic acid amide, maleic acid imide, etc. It is done.
In this specification, the term “(meth) acryl” means either “methacryl” or “acryl”.
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.
Furthermore, it is preferable that the acrylic monomer contains methyl methacrylate in that it can exhibit excellent foamability when foaming the foamable polymer of the acrylic monomer.
Moreover, as said acrylic monomer, it is preferable to contain maleic anhydride and methacrylamide in the point which can provide high heat resistance to the acrylic resin foam obtained.

(styrene)
It is important that the styrene is contained in the polymerizable monomer in an amount of 30% by mass or more. Thereby, the manufacturing method of the acrylic resin foam of this embodiment can manufacture the acrylic resin foam which is hard to produce the volume change by a heat | fever.
Although this mechanism is not certain, the following mechanism can be considered. That is, when the polymerizable monomer contains a large amount of styrene, the polymer in the obtained foam contains a large amount of benzene rings. As a result, it is considered that the polymer skeleton is strong and the foam is unlikely to undergo a volume change due to heat.
When urea is used as a foaming agent to be described later, the styrene is contained in the polymerizable monomer in an amount of 55% by mass or less from the viewpoint of containing a large amount of a water-soluble acrylic monomer exhibiting excellent solubility in urea. It is preferable that

(Acrylic monomers and polymerizable monomers other than styrene)
In addition, as a polymerizable monomer other than the acrylic monomer and styrene, a monomer copolymerizable with the acrylic monomer can be contained in a small amount in a polymerizable solution for the purpose of modifying an acrylic resin foam. .

In the polymerizable solution in the present embodiment, 5 to 40% by mass of the polymerizable monomer contained is methyl methacrylate, 14 to 35% by mass is (meth) acrylic acid, and 30 to 55% by mass is styrene. It is preferable that 1.0-10 mass% is maleic anhydride and 1.0-10 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 thermally decomposable foaming agent include urea, urea derivatives, dinitrosopentamethylenetetramine, amidoguanidine, trimethylenetriamine, paratoluenesulfone hydrazine, azodicarbonamide, thiourea, ammonium chloride, dicyandiamide, dioxane, hexane, water hydrate. 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)
In the present embodiment, the polymerizable solution may further contain a 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.

(Reducing agent)
In this 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.

(Dehydrating agent)
Furthermore, in the present embodiment, the polymerizable solution can further contain a dehydrating agent.
As the dehydrating agent, sulfates such as anhydrous sodium sulfate and anhydrous magnesium sulfate, and zeolite such as molecular sieve can be preferably used. For example, the content of the dehydrating agent in the polymerizable solution is preferably 0.01 to 50 parts by mass when the total amount of the polymerizable monomers in the polymerizable solution is 100 parts by mass. Such a dehydrating agent is desirably mixed and stirred at the time of preparing the polymerizable solution to dehydrate the water in the solution, and then removed by filtration.

(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.

Next, the acrylic resin foam according to this embodiment will be described.
The acrylic resin foam according to the present embodiment is prepared by preparing a polymerizable solution containing a polymerizable monomer containing an acrylic monomer and styrene, a thermal decomposable foaming agent, and a polymerization initiator. It is an acrylic resin foam obtained by foaming the foamable polymer obtained by the polymerization after polymerization.

  It is important that the polymerizable monomer contains 30% by mass or more of styrene. The polymerizable monomer preferably contains 55% by mass or less of styrene.

  Among the polymerizable monomers contained in the polymerizable solution, 5 to 40% by mass is methyl methacrylate, 14 to 35% by mass is (meth) acrylic acid, 30 to 55% by mass is styrene, It is preferable that 0-10 mass% is maleic anhydride and 1.0-10 mass% is methacrylamide.

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 is measured by a method based on the method described in JIS K 7222-1999. Specifically, the mass of a test piece of 10 cm ³ or more cut so as not to change the original cell structure is measured, and the apparent density is calculated by the following formula.
Apparent density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm 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 of the acrylic resin foam which concerns on this embodiment had the said advantage by the said structure, the manufacturing method of the acrylic resin foam of this invention is not limited to the said structure. The design can be changed as appropriate.

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

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

(Apparent density of acrylic resin foam)
The apparent density 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. 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 (%) = (Volume after heating−Volume before heating) / Volume before heating × 100
Moreover, the volume of the foam was calculated | required 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 foams of Examples and Comparative Examples 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.

Example 1
As a polymerization initiator for 100 parts by mass of a polymerizable monomer consisting of 30% by mass of methyl methacrylate, 25% by mass of methacrylic acid, 33% 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, 1.7 parts by mass of diisobutyl adipate as a plasticizer, urea 5 as a blowing agent 0.0 parts by mass was mixed and heated and stirred at 35 ° C., followed by filtration to remove residual inorganic salts, thereby preparing 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.
Then, the foamable polymer was obtained by heating the polymerizable solution together with the mold at 40 ° C. for 25 hours.
Thereafter, 41 g of the obtained foamable polymer is cut out, put into a mold having an internal method of 100 mm × 100 mm × 100 mm, and the foamable polymer is foamed with an acrylic resin by heating the mold together with the mold at 180 ° C. for 2 hours. A body (apparent density: 0.041 g / cm ³ ) was obtained.
Further, 116 g of the obtained foamable polymer was cut out, placed in 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: 0.116 g / cm ³ ) was obtained.

(Example 2)
The apparent density was 0.041 g / cm ^{3 in the same} manner as in Example 1 except that the methyl methacrylate concentration and the styrene concentration in the polymerizable monomer were 19 mass% and 44 mass%, respectively. An acrylic resin foam was obtained.

(Example 3)
The apparent density is 0.041 g / cm ^{3 in the same} manner as in Example 1 except that the concentration of methyl methacrylate and the concentration of styrene in the polymerizable monomer are 8 mass% and 55 mass%, respectively. And an acrylic resin foam having an apparent density of 0.116 g / cm ³ .

(Comparative Example 1)
The apparent density is 0.041 g / cm ^{3 in the same} manner as in Example 1 except that the concentration of methyl methacrylate and the concentration of styrene in the polymerizable monomer are 47% by mass and 16% by mass, respectively. An acrylic resin foam was obtained.

(Comparative Example 2)
The apparent density is 0.041 g / cm ^{3 in the same} manner as in Example 1 except that the concentration of methyl methacrylate and the concentration of styrene in the polymerizable monomer are 35% by mass and 28% by mass, respectively. And an acrylic resin foam having an apparent density of 0.116 g / cm ³ .

(Reference Example 1)
A polymerizable solution was prepared in the same manner as in Example 1 except that the methyl methacrylate concentration and the styrene concentration in the polymerizable monomer were 3% by mass and 60% by mass, respectively. The polymerization was not carried out because it did not dissolve sufficiently and part of the urea was removed as a residue.

  The test results are shown in Table 1.

As shown in Table 1, the acrylic resin foams of Examples 1 to 3 within the scope of the present invention are compared to Comparative Examples 1 and 2 using a polymerizable monomer having a styrene concentration of 28% by mass or less. The absolute value of the volume change rate due to 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 (4)

A polymerizable solution containing an acrylic monomer and a polymerizable monomer containing styrene, a thermal decomposable foaming agent, and a polymerization initiator is prepared, and after the polymerizable monomer is polymerized, foaming obtained by the polymerization is performed. The acrylic polymer foam is produced by foaming the functional polymer,
A method for producing an acrylic resin foam, wherein a monomer containing 30% by mass or more of styrene is used as the polymerizable monomer.   As said polymerizable monomer, methyl methacrylate 5-40 mass%, (meth) acrylic acid 14-35 mass%, styrene 30-55 mass%, maleic anhydride 1.0-10 mass%, and methacrylamide 1. The manufacturing method of the acrylic resin foam of Claim 1 using what contains 0-10 mass%. A polymerizable solution containing an acrylic monomer and a polymerizable monomer containing styrene, a thermal decomposable foaming agent, and a polymerization initiator is prepared, and after the polymerizable monomer is polymerized, foaming obtained by the polymerization is performed. Obtained by foaming a functional polymer,
An acrylic resin foam in which the polymerizable monomer contains 30% by mass or more of styrene.   The polymerizable monomer is methyl methacrylate 5 to 40% by mass, (meth) acrylic acid 14 to 35% by mass, styrene 30 to 55% by mass, maleic anhydride 1.0 to 10% by mass, and methacrylamide 1. The acrylic resin foam of Claim 3 containing 0-10 mass%.