JP5923398B2 - Acrylic resin foam and method for producing the same - Google Patents

Description

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

Conventionally, an acrylic resin foam (hereinafter also referred to as “foam”) has excellent strength, light weight, and excellent heat insulation properties. Therefore, by attaching fiber reinforced plastics (FRP) to the surface, It is used as a member for constructing an aircraft body, a wall material for a cold room of a cargo vehicle, a hull of a small boat, a wing of wind power generation, a table for an X-ray machine for transmitting X-rays, and the like.
Such an acrylic resin foam is usually prepared by mixing a polymerizable monomer containing an acrylic monomer with a polymerizable solution containing urea as a foaming agent and a polymerization initiator, as shown in Patent Document 1 below. After producing and pouring the polymerizable solution into a mold and heating the mold together to polymerize the acrylic monomer, the resulting foamable polymer is further heated to a high temperature to decompose urea. A method such as gas foaming is employed. 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

  In recent years, there has been a demand for an acrylic resin foam having further excellent heat resistance. The heat resistance of the acrylic resin foam described in Patent Document 1 is 160 ° C. or less, which is more excellent in heat resistance. Currently, acrylic resin foams are awaited.

  This invention makes it a subject to provide the acrylic resin foam excellent in heat resistance in view of the said problem.

  The present inventors have intensively studied to solve the above problems, and found that the heat resistance of the acrylic resin foam can be improved by containing 36% by mass or more of methacrylic acid in the polymerizable monomer. The present invention has been completed.

  In the present invention, a polymerizable solution containing a polymerizable monomer containing 36% by mass or more of methacrylic acid, a foaming agent containing a thermally decomposable foaming agent, and a polymerization initiator was prepared, and the polymerizable monomer was polymerized. The acrylic resin foam is obtained by foaming a foamable polymer obtained by the polymerization.

  The present invention also provides a polymerizable solution containing a polymerizable monomer containing 36% by mass or more of methacrylic acid, a foaming agent containing a pyrolytic foaming agent, and a polymerization initiator, and polymerizing the polymerizable monomer. And then producing an acrylic resin foam by foaming the foamable polymer obtained by the polymerization.

According to the present invention, an acrylic resin foam excellent in heat resistance can be provided by containing 36% by mass or more of methacrylic acid in the polymerizable monomer.
Furthermore, according to this invention, the manufacturing method of the acrylic resin foam excellent in the hardness with a small average bubble diameter 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, 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 heated to a temperature equal to or higher than the temperature at which the thermally decomposable foaming agent is decomposed and foamed to produce an acrylic resin foam.
Hereinafter, the components of the polymerizable solution will be described.

(Acrylic monomer)
As the acrylic monomer, an acrylic monomer containing methacrylic acid is used.
The polymerizable monomer contains 36% by mass or more of methacrylic acid. The polymerizable monomer preferably contains methacrylic acid in an amount of 40 to 60% by mass, more preferably 45 to 60% by mass. When the polymerizable monomer contains 36% by mass or more of methacrylic acid, there is an advantage that the resulting acrylic resin foam has excellent heat resistance. Moreover, when the said polymerizable monomer contains 36 mass% or more of methacrylic acid, there also exists an advantage that the average cell diameter of the acrylic resin foam obtained can be made small. The acrylic resin foam has an advantage that the hardness becomes high when the average cell diameter is small.
In addition, if the polymerizable monomer contains methacrylic acid in excess, bubbles may not be generated at the time of foaming and an acrylic resin foam may not be obtained. Therefore, the methacrylic acid content of the polymerizable monomer is 60% by mass. The following is desirable.

The acrylic monomer preferably contains maleic anhydride and methacrylamide in that high acrylic resin foam can be provided with high heat resistance.
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 methacrylic acid, maleic anhydride, methacrylamide, and methyl methacrylate, maleic acid, fumaric acid, itaconic acid, itaconic anhydride, crotonic acid, acrylic 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.
In this specification, the term “(meth) acryl” means either “methacryl” or “acryl”.

(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, the polymerizable monomer is 14 to 36% by mass of methyl methacrylate, 36 to 60% by mass of methacrylic acid, 10 to 20% by mass of styrene, 1.0 to 10% by mass of maleic anhydride, and methacrylic acid. It is preferable to contain 1.0-10 mass% of amides. 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.
The polymerizable monomer is preferably substantially composed of methyl methacrylate, methacrylic acid, styrene, maleic anhydride, and methacrylamide. Specifically, methyl methacrylate, methacrylic acid, styrene, The total amount of maleic anhydride and methacrylamide is preferably 85% by mass or more, more preferably 90 to 100% by mass.

(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 and urea derivatives are suitable foaming agents.
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. Acid esters and the like can be 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.
As the plasticizer, dioctyl phthalate, diisobutyl adipate, tributyl acetylcitrate and the like are preferably used.
By using a plasticizer, the foamability of the foamable polymer can be improved. On the other hand, if used excessively, the rigidity of the acrylic resin foam may decrease, the bubbles of the acrylic resin foam may become coarse, or the acrylic resin foam may shrink during foaming. When the total amount of the polymerizable monomer is 100 parts by mass, it is preferably contained in the polymerizable solution at a ratio of 0.1 to 20 parts by mass, more preferably 0.3 to 10 parts by mass, ˜5 parts by mass is particularly preferred.

(Chain transfer agent)
In the present embodiment, the polymerizable solution may further contain a chain transfer agent.
As the chain transfer agent, α-methylstyrene dimer, n-octyl mercaptan, or the like is used.
If the amount of the chain transfer agent is small, the molecular weight of the resulting resin may be large and foamability may be reduced. If the amount is large, the polymerization time may be increased and the monomer component may take a long time to cure. When the total amount is 100 parts by mass, it is preferably contained in the polymerizable solution at a ratio of 0.01 to 1 part by mass, more preferably 0.05 to 0.5 part by mass, and 0.08 to 0.15 parts by mass is particularly preferable.

(Reducing agent)
In the present embodiment, when a redox polymerization initiator is used in the polymerizable solution, a reducing agent can be further contained. The addition of the reducing agent has the effect of promoting the polymerization reaction in order to improve the radical generation efficiency from the polymerization initiator.
As the reducing agent, a compound that can reduce other compounds (donate electrons) 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.
Further, the metal ion functions as an electron-donating substance, that is, an oxidizing agent, or an electron-donating substance, that is, a reducing agent, in the polymerizable solution, and accelerates the polymerization reaction of the polymerizable monomer. It contributes to.
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 sodium sulfate and 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.

(Polymerization inhibitor)
In the present embodiment, the polymerizable solution may further contain a polymerization inhibitor in order to suppress a polymerization reaction between single monomers or a rapid polymerization reaction.
Examples of the polymerization inhibitor include alkaline earth metal salts, that is, salts of beryllium, magnesium, calcium, strontium, barium, and radium, and examples include calcium formate. Content in a polymeric solution can be contained in the ratio used as 0.001-5 mass parts, for example, when the total amount of the polymerizable monomer in a polymeric solution is 100 mass parts. By containing the polymerization inhibitor, the polymerizable solution has an advantage that it can suppress excessive polymerization when the polymerizable monomer is polymerized.

(Bubble conditioner)
Furthermore, in the present embodiment, the polymerizable solution may further contain a bubble regulator. The addition of the bubble regulator has the effect of improving the uniformity of the bubble diameter in the foam.
Examples of the air conditioner include powdery inorganic substances such as alkaline earth metal salts, metal oxides, silica gel, and diatomaceous earth.
The content of such a bubble regulator in the polymerizable solution can be contained in a ratio of 0.01 to 10 parts by mass, when the total amount of polymerizable monomers in the polymerizable solution is 100 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. There is an advantage that it becomes 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. There is an 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 produces a polymerizable solution containing a polymerizable monomer containing 36% by mass or more of methacrylic acid, a foaming agent containing a pyrolytic foaming agent, and a polymerization initiator, It is an acrylic resin foam obtained by polymerizing the polymerizable monomer and then foaming the foamable polymer obtained by the polymerization.

Further, the heat resistant temperature in TMA (thermomechanical analysis) of the acrylic resin foam according to the present embodiment is preferably 170 ° C. or higher, more preferably 180 ° C. or higher, and 190 ° C. or higher. Particularly preferred.
In addition, the heat-resistant temperature in a thermomechanical analysis is measured as follows.
That is, 7 mm (length) x 7 mm (width) x 2 mm (thickness) rectangular parallelepiped foam was cut out to produce a test piece, and a compression test mode (indenter tip φ3 mm, quartz probe using thermomechanical analyzer) ) 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 rate of temperature increase of 5 ° C./min. The thickness of the test piece is 10% of the thickness of the test piece before the test. The temperature at the time of contraction 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, the average cell diameter of the acrylic resin foam according to this embodiment is preferably 0.4 mm or less, and more preferably 0.1 to 0.3 mm.
When the average cell diameter is 0.3 mm or less, there is an advantage that the acrylic resin foam is excellent in hardness. Moreover, there exists an advantage that the light transmittance of an acrylic resin foam is excellent because an average bubble diameter is 0.1 mm or more.
The average bubble diameter is calculated as follows.
That is, the acrylic resin foam was cut, and the cut surface of the portion excluding the outside 1/10 in the cut surface thickness direction was magnified 18 times using a scanning electron microscope, Print the image on 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.

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 the present embodiment is configured as described above, it has the following advantages.
That is, the acrylic resin foam according to the present embodiment is an acrylic resin foam obtained by adding 36% by mass or more of methacrylic acid to a polymerizable monomer, and thus, an acrylic resin foam excellent in heat resistance. Has the advantage of becoming a body. Moreover, the acrylic resin foam according to the present embodiment is an acrylic resin foam obtained by adding 36% by mass or more of methacrylic acid to the polymerizable monomer, so that an acrylic resin foam having a small average cell diameter is obtained. It also has the advantage of body. The acrylic resin foam has an advantage that the hardness becomes high when the average cell diameter is small.

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

  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 a foamable polymer and an acrylic resin foam will be described.

(Density of foamable polymer)
About the test piece of 10 cm < ³ > or more cut | disconnected so that a crack might not arise in an expandable polymer, the mass was measured and the density was computed by following Formula.
Density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )

(Apparent density of acrylic resin foam)
The apparent density of the acrylic resin foam was 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 was measured, and the apparent density was calculated by the following formula.
Apparent density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )

(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.
Specifically, a foam is cut out into a 7 mm (length) × 7 mm (width) × 2 mm (thickness) rectangular parallelepiped shape to produce a test piece, and a heat / stress / strain measuring device (SII Nanotechnology Co., Ltd.) Product name “EXSTRAR TMA / SS6100”), compression test mode (indenter tip φ3 mm, quartz probe), load 100 mN, indenter is applied to test piece at 30 ° C. and heating rate 5 ° C./min. The temperature was raised and the temperature when the thickness of the test piece contracted 10% with respect to the thickness of the test piece before the test was measured, and this temperature was defined as the heat resistant temperature in TMA.
Note that correction was made by setting the quartz coefficient before analysis. The thickness of the test piece was measured by applying an indenter with a load of 100 mN to the test piece before measurement.

(Average cell diameter of acrylic resin foam)
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.) and totaled Four cut surfaces were photographed, and images of the photographed cut surfaces were each printed on A4 paper.
Next, six arbitrary line segments (length 60 mm) were drawn for each A4 sheet, and the average chord length for each line segment was calculated from the number of bubbles overlapping the line segment by the following equation. However, the line segment was drawn as much as possible so that the bubbles would not touch only at the contact points, and if they were touched, they were included in the number of bubbles.
Average chord length (t) = length of line segment / (number of bubbles x photo magnification)
And the bubble diameter D was computed by following Formula.
D = t / 0.616
And the arithmetic average value of the bubble diameter D calculated | required for every line segment was calculated | required, and this arithmetic average value was made into the average bubble diameter of an acrylic resin foam.

The hardness of the obtained foam was measured as follows.
That is, a test piece of 150 mm (length) × 150 mm (width) × 100 mm (thickness) was produced from the obtained foam. 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 A type (manufactured by Kobunshi Keiki Co., Ltd.). And the measured value 30 seconds after reading the test piece on the pressing surface was read. The measurement was performed on six test pieces, and the average value was taken as the hardness.

(Example 1: Preparation of polymerizable solution)
As a polymerization initiator for 100 parts by mass of a polymerizable monomer comprising 25% by mass of methyl methacrylate, 47% 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 weight, 0.2 part by weight of calcium formate as a polymerization inhibitor, 2.0 parts by weight of sodium sulfate as a dehydrating agent, 0.1 part by weight of α-methylstyrene dimer as a chain transfer agent, 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.

(Example 1: Production of foamable polymer and acrylic resin foam)
1500 g of the polymerizable solution of Example 1 was placed in a Teflon rectangular parallelepiped mold having an internal method of 25 mm × 200 mm × 360 mm.
Then, the polymerizable solution was heated at 50 ° C. for 10 hours together with the mold, and then heated at 80 ° C. for 3 hours to obtain a foamable polymer (density: 1.16 g / cm ³ ).
Then, the foamable polymer is put into a hot air circulating furnace and heated to a temperature at which urea (thermal decomposition temperature: 135 ° C.) is decomposed or more (specifically, heated at a furnace temperature of 180 ° C. for 2 hours) The foaming agent (urea) was decomposed and foamed to produce an acrylic resin foam (apparent density: 0.116 g / cm ³ ).

(Example 2: Preparation of polymerizable solution)
Instead of the chain transfer agent α-methylstyrene dimer, dioctyl phthalate (DOP) was used as a plasticizer, and dioctyl phthalate (DOP) 2.0 parts by mass was mixed with 100 parts by mass of the polymerizable monomer. A polymerizable solution was prepared in the same manner as in Example 1 except that.

(Example 2: Production of foamable polymer and acrylic resin foam)
The polymerizable solution of Example 2 was used instead of the polymerizable solution of Example 1, and the heating conditions of the polymerizable solution were changed (specifically, the polymerizable solution was placed at 40 ° C. together with the mold) A foamable polymer and an acrylic resin foam were prepared in the same manner as in Example 1 except that the foamable polymer was obtained by heating for 25 hours. The density of the foamable polymer was 1.16 g / cm ³ . The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Example 3: Preparation of polymerizable solution)
Polymerization was performed in the same manner as in Example 2 except that the content of methyl methacrylate in the polymerizable monomer was 36% by mass and the content of methacrylic acid in the polymerizable monomer was 36% by mass. A solution was made.

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

(Example 4: Preparation of polymerizable solution)
Polymerization was performed in the same manner as in Example 2 except that the content of methyl methacrylate in the polymerizable monomer was 12% by mass and the content of methacrylic acid in the polymerizable monomer was 60% by mass. A solution was made.

(Example 4: Production of foamable polymer and acrylic resin foam)
A foamable polymer and an acrylic resin foam were produced in the same manner as in Example 2 except that the polymerizable solution of Example 4 was used instead of the polymerizable solution of Example 2. The density of the foamable polymer was 1.16 g / cm ³ . The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Comparative Example 1: Preparation of polymerizable solution)
Polymerization was performed in the same manner as in Example 1 except that the content of methyl methacrylate in the polymerizable monomer was 47% by mass and the content of methacrylic acid in the polymerizable monomer was 25% by mass. A solution was made.

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

(Comparative Example 2: Preparation of polymerizable solution)
Instead of the chain transfer agent α-methylstyrene dimer, dioctyl phthalate (DOP) was used as a plasticizer, and dioctyl phthalate (DOP) 2.0 parts by mass was mixed with 100 parts by mass of the polymerizable monomer. Except for this, a polymerizable solution was prepared in the same manner as in Comparative Example 1.

(Comparative Example 2: Production of foamable polymer and acrylic resin foam)
The polymerizable solution of Comparative Example 2 was used instead of the polymerizable solution of Example 1, and the heating conditions of the polymerizable solution were changed (specifically, the polymerizable solution was 43.5 for each mold). A foamable polymer and an acrylic resin foam were produced in the same manner as in Example 1 except that a foamable polymer was obtained by heating at ° C for 21 hours. The density of the foamable polymer was 1.16 g / cm ³ . The apparent density of the acrylic resin foam was 0.116 g / cm ³ .

(Comparative Example 3: Preparation of polymerizable solution)
The content of methyl methacrylate in the polymerizable monomer was 57% by mass, the content of methacrylic acid in the polymerizable monomer was 14% by mass, and the content of styrene in the polymerizable monomer was 13% by mass. A polymerizable solution was prepared in the same manner as in Comparative Example 1 except that the content of methacrylamide in the polymerizable monomer was 8.0% by mass.

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

  The test results are shown in Table 1.

As shown in Table 1, the acrylic resin foams of Examples 1 to 4 within the scope of the present invention were prepared as Comparative Examples 1 using a polymerizable monomer having a methacrylic acid content of less than 36% by mass. As compared with the acrylic resin foam of ˜3, the heat resistant temperature in the thermomechanical analysis showed a high value.
Therefore, according to this invention, the acrylic resin foam excellent in heat resistance compared with the past can be provided.
In addition, the acrylic resin foams of Examples 1 to 4 within the scope of the present invention are acrylic systems of Comparative Examples 1 to 3 prepared using a polymerizable monomer having a methacrylic acid content of less than 36% by mass. The average cell diameter was smaller than that of the resin foam. Accordingly, a high hardness value was exhibited.
Therefore, the present invention also has an advantage that it is possible to provide an acrylic resin foam having a small average cell diameter and higher hardness than before.

Claims (5)

A polymerizable solution containing a polymerizable monomer containing 36% by mass or more of methacrylic acid, a foaming agent containing a thermal decomposable foaming agent, and a polymerization initiator is prepared, and after polymerization of the polymerizable monomer, the polymerization obtained by foaming the resulting expandable polymer by,
The polymerizable monomer is methyl methacrylate 12 to 36% by mass, methacrylic acid 36 to 60% by mass, styrene 10 to 20% by mass, maleic anhydride 1.0 to 10% by mass, and methacrylamide 1.0 to 10% by mass. acrylic resin foam characterized that you containing mass%. The acrylic resin foam according to claim 1 , wherein the average cell diameter is 0.1 to 0.3 mm.   The acrylic resin foam according to claim 1 or 2, wherein the heat-resistant temperature in thermomechanical analysis is 170 ° C or higher. The acrylic resin foam according to any one of claims 1 to 3 , wherein an apparent density is 0.15 g / cm ³ or less. A polymerizable solution containing a polymerizable monomer containing 36% by mass or more of methacrylic acid, a foaming agent containing a thermal decomposable foaming agent, and a polymerization initiator is prepared, and after polymerization of the polymerizable monomer, the polymerization obtained by foaming the foamable polymer to produce an acrylic resin foam by,
The polymerizable monomer is methyl methacrylate 12 to 36% by mass, methacrylic acid 36 to 60% by mass, styrene 10 to 20% by mass, maleic anhydride 1.0 to 10% by mass, and methacrylamide 1.0 to 10% by mass. method for producing an acrylic resin foam characterized that you containing mass%.