JP6106008B2 - 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, and therefore have a fiber reinforced plastic (FRP) (carbon fiber reinforced plastic) on the surface. (CFRP) etc.) Laminate sheets to form automobile bodies, small boat hulls, cargo vehicle cold room wall materials, wind power wings, X-ray transmission tables for X-ray transmission, etc. It is used as a member for this purpose.
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, a board having an acrylic resin foam as the core material and an FRP sheet as the surface material is required to exhibit excellent strength in the thickness direction, and is required to be less susceptible to dimensional changes due to external pressure. ing.
In response to such a request, it is conceivable to improve the strength in the thickness direction of the core material by reducing the expansion ratio of the acrylic resin foam, but in that case, the lightness and heat insulation of the board may be impaired. Have
In addition, the acrylic resin foam is used for various applications as described above, and it is not limited to the core material that is required to suppress dimensional changes due to external pressure.
In addition, the acrylic resin foam is used in various shapes other than the board shape, and the application of external pressure is not necessarily limited to the thickness direction.
That is, the problem that a particularly effective method has not been established other than the method of increasing the apparent density as a method of suppressing the dimensional change with respect to the external force applied from one direction is a problem common to all acrylic resin foams.

  In view of the above problems, the present invention provides a method for producing an acrylic resin foam capable of producing an acrylic resin foam that hardly undergoes a dimensional change due to external pressure from one direction for the apparent density. One object is to provide an acrylic resin foam that hardly undergoes dimensional changes due to external pressure from one direction for the apparent density.

The present invention relates to a foamable polymer in which a foaming agent containing a pyrolytic foaming agent is dispersed in a polymer obtained by polymerizing a polymerizable monomer containing an acrylic monomer,
Using a mold having a rectangular parallelepiped internal space,
Comprising the step of forming an acrylic resin foam by heating the foamable polymer accommodated in the mold above the thermal decomposition temperature of the pyrolytic foaming agent;
In the step, the acrylic resin foam production method for producing a rectangular parallelepiped acrylic resin foam by substantially filling the acrylic resin foam in the mold,
When the inner dimensions of the mold in the vertical direction, the horizontal direction, and the height direction are Bx, By, and Bz, respectively, the foamable polymer contained in the mold is expressed by the following relational expressions (1) and (2). It is in the manufacturing method of the acrylic resin foam characterized by making it the rectangular parallelepiped shape which satisfy | fills.
(Bz / Az) / (Bx / Ax)> 1.00 (1)
(Bz / Az) / (By / Ay)> 1.00 (2)
(However, “Ax” in the formula represents the longitudinal dimension of the foamable polymer, “Ay” in the formula represents the lateral dimension of the foamable polymer, and “Az” in the formula represents the foamable property. (Dimensions in the height direction of the polymer are shown.)

  Such a method for producing an acrylic resin foam is obtained by making the foamable polymer accommodated in the mold into a rectangular parallelepiped shape satisfying the above relational expressions (1) and (2). As a result, it is easy to increase the bubble diameter in one direction compared to the bubble diameter in the other direction, and as a result, the acrylic resin is less susceptible to dimensional change due to external pressure from one direction for the apparent density. It has the advantage that a foam can be produced.

In the present invention, when the average bubble diameter in one direction is Hz, and the average bubble diameter in each of two directions orthogonal to the one direction and orthogonal to each other is Hx, Hy,
The acrylic resin foam is characterized in that Hz / Hx is 1.10 or more and Hz / Hy is 1.10 or more.

  Such an acrylic resin foam has an external pressure from one direction for the apparent density because Hz / Hx is 1.10 or more and Hz / Hy is 1.10 or more. There is an advantage that the dimensional change due to is difficult to occur.

  ADVANTAGE OF THE INVENTION According to this invention, the acrylic resin foam which a dimensional change by the external pressure from one direction cannot produce easily 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 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 to contain methyl methacrylate in the acrylic monomer 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.

(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, if the styrene monomer is contained excessively, the hardness may be impaired, so the content of the styrene monomer in the polymerizable monomer is preferably 30% by mass or less.

More specifically, in the polymerizable solution in the present embodiment, 50 to 70% by mass of the polymerizable monomer contained is methyl methacrylate, 14 to 27% by mass is (meth) acrylic acid, It is preferable that 30% by mass is styrene.
An acrylic resin foam produced using such a polymerizable solution has an advantage of being excellent in compressive strength.
In addition, all (meth) acrylic acid contained in the ratio of 14 to 27 mass% may be methacrylic acid, or 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.

Moreover, when the polymerizable solution in this embodiment contains maleic anhydride and methacrylamide, 35 to 60% by mass of the polymerizable monomer contained is methyl methacrylate and 14 to 35% by mass. (Meth) acrylic acid, preferably 10 to 20 mass% is styrene, 1.0 to 10 mass% is maleic anhydride, and 1.0 to 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 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)
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.
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 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.

In the method for producing an acrylic resin foam of the present embodiment, a polymerizable solution containing the above-described constituent components is prepared, and a polymerizable monomer contained in the polymerizable solution is polymerized to obtain a foamable polymer. The foamable polymer is obtained by dispersing a foaming agent containing a thermally decomposable foaming agent in a polymer obtained by polymerizing a polymerizable monomer containing an acrylic monomer.
Moreover, in the manufacturing method of the acrylic resin foam of this embodiment, the foamable polymer accommodated in the mold using the foamable polymer and a mold having a rectangular parallelepiped internal space. The step of forming an acrylic resin foam by performing heating at a temperature equal to or higher than the thermal decomposition temperature of the pyrolytic foaming agent is performed. At the said process, the said acrylic resin foam is substantially filled in the said shaping | molding die, and a rectangular parallelepiped acrylic resin foam is produced.

In the step, the foamable polymer is heated to a temperature equal to or higher than the thermal decomposition temperature of the thermally decomposable foaming agent to start foaming of the foamable polymer to form an acrylic resin foam in the mold. And the second step of increasing the apparent volume of the acrylic resin foam by continuing the heating and substantially filling the acrylic resin foam into the mold. Thus, an acrylic resin foam having a shape corresponding to the internal space of the mold is produced.
In the second step, the increase in volume of the acrylic resin foam is performed in one direction before the completion of the second step. By this implementation, it is possible to produce an acrylic resin foam in which the average length of the bubbles in the direction is longer than the average bubble diameter in a plane orthogonal to the direction.

Specifically, in the step, when the inner dimensions in the vertical direction, the horizontal direction, and the height direction of the mold are Bx, By, and Bz, respectively, the foamable polymer to be accommodated in the mold is A rectangular parallelepiped that satisfies the relational expressions (1) and (2) is used.
(Bz / Az) / (Bx / Ax)> 1.00 (1)
(Bz / Az) / (By / Ay)> 1.00 (2)
(However, “Ax” in the formula represents the longitudinal dimension of the foamable polymer, “Ay” in the formula represents the lateral dimension of the foamable polymer, and “Az” in the formula represents the foamable property. (Dimensions in the height direction of the polymer are shown.)
(Bz / Az) / (Bx / Ax) is preferably 1.10 to 3.00, and more preferably 1.20 to 1.40.
Further, (Bz / Az) / (By / Ay) is preferably 1.10 to 3.00, and more preferably 1.20 to 1.40.
In the method for producing an acrylic resin foam according to this embodiment, the foamable polymer to be accommodated in the mold is a rectangular solid satisfying the above relational expressions (1) and (2). For foam, it is easy to make the bubble diameter in one direction larger than the bubble diameter in the other direction, and as a result, acrylic that hardly changes in dimensions due to external pressure from one direction for the apparent density. This has the advantage that a resin foam can be produced.
Further, in the method for producing an acrylic resin foam according to the present embodiment, when the foamable polymer is disposed in the mold, the inner dimension of the mold is in the vertical direction, the horizontal direction, and the height direction. The foaming polymer preferably has a longitudinal direction, a lateral direction, and a height direction that are parallel to each other.
Furthermore, in the method for producing an acrylic resin foam according to the present embodiment, when the foamable polymer is disposed on the mold, the bottom surface of the foamable polymer is approximately at the center of the bottom surface of the inner space of the mold. It is preferable that the center of is located.

Next, the acrylic resin foam according to this embodiment will be described.
In the acrylic resin foam according to this embodiment, most of the bubbles extend in one direction, and this one direction is a direction in which external pressure is applied to the acrylic resin foam.
The acrylic resin foam according to the present embodiment has an average cell diameter in one direction as Hz, and the average cell diameter in two directions orthogonal to the one direction and orthogonal to each other is Hx. , Hy, Hz / Hx is 1.10 or more, and Hz / Hy is 1.10 or more. In the acrylic resin foam according to the present embodiment, Hz / Hx is 1.10 or more and Hz / Hy is 1.10 or more, so that the one direction for the apparent density. Therefore, there is an advantage that the dimensional change due to the external pressure is less likely to occur.

Hx, Hy, and Hz are obtained as follows.
First, about an acrylic resin foam, a 10 mm x 10 mm x 10 mm square is cut out so that a gravity center may be included. If the acrylic resin foam is too small to cut out a 10 mm × 10 mm × 10 mm square, cut out as much as possible.
Then, using a scanning electron microscope (for example, “S-3000N” manufactured by Hitachi, Ltd.), the magnification is 18 to 100 times, one direction, orthogonal to the one direction, and each other The cut surfaces in two directions perpendicular to each other are photographed, and images of the photographed cut surfaces are printed on A4 paper, respectively. At this time, the magnification of the electron microscope is adjusted so that the number of bubbles is 10 or more on a 60 mm straight line drawn on the printed photograph, and the photographed cut surface image is on A4 paper. Print four images at a time.
Next, in an image obtained by photographing a cut surface in one direction, two directions (a first other direction and a second other direction) that are orthogonal to the one direction and are orthogonal to each other. Arbitrary line segments (length: 60 mm) are drawn at six locations, 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)
The magnification of the photograph is obtained by the following equation by measuring the scale bar on the photograph to 1/100 mm with “Digimatic Caliper” manufactured by Mitutoyo Corporation.
Photo magnification = Scale bar measured value (mm) / Scale bar display value (mm)
Then, the bubble diameter D is calculated by the following formula.
D = t / 0.616
Similarly, with respect to the image obtained by photographing the cut surface in the first other direction, six arbitrary line segments (length: 60 mm) are drawn in each of the one direction and the second other direction to obtain the bubble diameter. Ask for.
Further, similarly for the image obtained by photographing the cut surface in the second other direction, six arbitrary line segments (length: 60 mm) are drawn in each of the one direction and the first other direction, and the bubble diameter is determined. Ask for.
And the geometric mean value of the bubble diameter for every direction is calculated | required from the bubble diameter D calculated | required for every line segment, and let this geometric mean value be the bubble diameter (Hz, Hy, and Hz) of each direction. In addition, let the maximum value be Hz among the obtained geometric mean values, and let the other geometric mean values be Hx and Hy.

In addition, for the acrylic resin foam according to the present embodiment, the finer the average cell diameter (overall average cell diameter), the better. However, at present, the average cell diameter is less than 0.3 mm (overall average cell diameter). Stable formation is difficult. In addition, when the acrylic resin foam is bonded to another member (such as an FRP sheet (CFRP sheet or the like)) via an adhesive (when combined), the amount of the adhesive that enters the void can be suppressed. In view of the above, the average bubble diameter (overall average bubble diameter) is preferably 1.3 mm or less, and more preferably 1.0 mm or less.
In addition, about the average cell diameter (overall average cell diameter) of an acrylic resin foam, a geometric average value is calculated | required from the cell diameter calculated | required for every direction, and this geometric average value is obtained by the average cell diameter ( Overall average bubble diameter).

Furthermore, the acrylic resin foam according to this embodiment preferably has an apparent density of 0.15 g / cm ³ or less, and more preferably 0.12 g / cm ³ or less, from the viewpoint of lightness. On the other hand, from the viewpoint of mechanical strength, the apparent density 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 the method described in Examples described later.

  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 )

(Average cell diameter in each direction of acrylic resin foam and overall average cell diameter)
A 10 mm × 10 mm × 10 mm square was cut out so as to include the center of gravity of the foam for the third piece obtained by dividing the foam into 5 parts in the thickness direction (the middle part of the 5 parts). Using a scanning electron microscope (“S-3000N” manufactured by Hitachi, Ltd.), the cut surface in the length direction, the width direction, and the height direction is magnified 18 times, and an image of the photographed cut surface is obtained. Four images were printed on each A4 paper.
Next, in an image obtained by photographing a cut surface in the length direction, arbitrary line segments (length 60 mm) are drawn in each of the width direction and the height direction, and each line segment is calculated from the number of bubbles overlapping the line segment. The average chord length of was calculated 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)
The magnification of the photograph was obtained from the following equation by measuring the scale bar on the photograph to 1/100 mm with “Digimatic Caliper” manufactured by Mitutoyo Corporation.
Photo magnification = Scale bar measured value (mm) / Scale bar display value (mm)
And the bubble diameter D was computed by following Formula.
D = t / 0.616
Similarly, for the image obtained by photographing the cut surface in the width direction, six arbitrary line segments (length: 60 mm) were drawn in the length direction and the height direction, respectively, and the bubble diameter was determined.
Further, for the image obtained by photographing the cut surface in the height direction, similarly, arbitrary line segments (length: 60 mm) were drawn in each of the length direction and the width direction to obtain the bubble diameter.
And the geometric mean value of the bubble diameter for every direction was calculated | required from the bubble diameter D calculated | required for every line segment, and this geometric average value was made into the bubble diameter of each direction.
Moreover, the geometric average value was calculated | required from the bubble diameter calculated | required for every direction, and this geometric average value was made into the average bubble diameter (overall average bubble diameter) of an acrylic resin foam.

(Apparent density of acrylic resin foam)
The apparent density of the acrylic resin foam was measured in accordance with the method described in JIS K 7222: 2005 “Foamed Plastics and Rubber—How to Obtain the Apparent Density”.
That is, a test piece was cut from a sample that had passed 72 hours or more after molding of the foam into a length of 25 mm, a width of 25 mm, and a thickness of 25 mm so as not to change the original bubble structure of the material. The sample was allowed to stand for 16 hours or more under atmospheric conditions of 50 ° C. and humidity of 50 ± 5%.
Apparent density (kg / m ³ ) = Mass of test piece (g) / Volume of test piece (mm ³ ) × 10 ⁶
For the measurement of dimensions, “DIGIMATIC” CD-15 type manufactured by Mitutoyo Corporation was used.

(Compressive strength of acrylic resin foam, strength at 5% compression, and compression modulus)
Measured in accordance with the method described in JIS K 7220: 2006 “Rigid foamed plastic-Determination of compression characteristics”.
That is, using Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.) and universal testing machine data processing (manufactured by UTPS-237S Softbrain Co., Ltd.), the size of the specimen is compressed with a cross section of 50 mm x 50 mm and a thickness of 50 mm. The compression strength σm up to 10% compression was measured at a speed of 5 mm / min. The number of specimens shall be three.
The test piece was conditioned for 16 hours or more in an environment of temperature 23 ± 2 ° C. and humidity 50 ± 5%, and then measured.
For the measurement of dimensions, “DIGIMATIC” CD-15 type manufactured by Mitutoyo Corporation was used.
The compressive strength σm is calculated by the following equation.
σm = Fm / A0 × 10 ³
σm: compression strength (kPa)
Fm: Maximum force reached within 10% deformation rate (N)
A0: Initial cross-sectional area of the test piece (mm ² )
The 5% compression strength σ5 is calculated by the following formula.
σ5 = F5 / A0 × 10 ³
σ5: Strength at 5% compression (kPa)
F5: Force when the deformation rate reaches 5% (N)
A0: Initial cross-sectional area of the test piece (mm ² )
The compression elastic modulus is calculated by the following equation using the first linear portion of the load-deformation curve.
E = Δσ / Δε
E: Compression elastic modulus (kPa)
Δσ: Stress difference between two points on the straight line (kPa)
Δε: Difference in deformation between the same two points (%)

Example 1
5 parts by mass of urea (thermal decomposition temperature: 132.7 ° C.) as a foaming agent is mixed with 100 parts by mass of a polymerizable monomer composed of 60% by mass of methyl methacrylate, 20% by mass of methacrylic acid, and 20% by mass of styrene. And it was made to melt | dissolve uniformly and the monomer solution was produced.
Furthermore, 0.48 parts by mass of t-butyl hydroperoxide (“Perbutyl H-69” manufactured by NOF Corporation) as a polymerization initiator and N, N-dimethyl as a reducing agent with respect to 100 parts by mass of the polymerizable monomer. 0.48 parts by mass of aniline, 0.06 part by mass of hexatrimethylammonium chloride (“Nissan Cation PB-300” manufactured by NOF Corporation) as a substance for adding chloride ions was added to the monomer solution, and these were stirred. A polymerizable solution was prepared.
1000 g of the polymerizable solution was placed in a glass cuboid mold having an internal method of 300 mm (length) × 120 mm (width) × 30 mm (height). And the foaming polymer (density: 1.15 g / cm < ³ >) was obtained by putting the polymeric solution into a thermostat with the mold and heating at 50 degreeC for 10 hours. At this time, it was confirmed that the foamable polymer was cured.
Thereafter, the foamable polymer obtained was cut into 159 mm (length) × 106 mm (width) × 25 mm (height), and a mold having an internal method of 300 mm (length) × 200 mm (width) × 70 mm (height) An acrylic resin foam (apparent density: 0.115 g / cm ³ ) was obtained by placing the foamable polymer together with the mold in a hot air circulating furnace and heating at 170 ° C. for 30 minutes. When the foamable polymer is disposed in the mold, the longitudinal direction, the lateral direction, and the height direction of the inner dimension of the mold, the longitudinal direction of the foamable polymer, the lateral direction, and The height directions are parallel to each other, and the center of the bottom surface of the foamable polymer is positioned substantially at the center of the bottom surface of the inner space of the mold.

(Examples 2-3 and Comparative Examples 1-2)
An acrylic resin foam was obtained in the same manner as in Example 1 except that the foamable polymer obtained in the same manner as in Example 1 was cut into the dimensions shown in Table 1.

  The test results are shown in Table 1.

As shown in Table 1, the acrylic resin foam of Example 2 that is within the scope of the present invention has the same expansion ratio, and the comparison was made with Hz / Hx and Hz / Hy being less than 1.10. Compared to the acrylic resin foam of Example 1, the compressive strength, 5% compressive strength, and compressive elastic modulus were higher.
Further, the acrylic resin foam of Example 3 within the scope of the present invention has the same expansion ratio, and the acrylic resin of Comparative Example 2 manufactured with Hz / Hx and Hz / Hy being less than 1.10. Compared to the resin foam, the compressive strength, 5% compressive strength, and compressive elastic modulus were higher.
Therefore, according to the present invention, it can be seen that an acrylic resin foam that is less likely to cause a dimensional change even if it is compressed relative to the size of the apparent density as compared with the prior art can be provided.

Claims (7)

A foamable polymer obtained by dispersing a foaming agent containing a thermally decomposable foaming agent in a polymer obtained by polymerizing a polymerizable monomer containing an acrylic monomer;
Using a mold having a rectangular parallelepiped internal space,
Comprising the step of forming an acrylic resin foam by heating the foamable polymer accommodated in the mold above the thermal decomposition temperature of the pyrolytic foaming agent;
In the step, the acrylic resin foam production method for producing a rectangular parallelepiped acrylic resin foam by substantially filling the acrylic resin foam in the mold,
When the inner dimensions of the mold in the vertical direction, the horizontal direction, and the height direction are Bx, By, and Bz, respectively, the foamable polymer contained in the mold is expressed by the following relational expressions (1) and (2). The manufacturing method of the acrylic resin foam characterized by making it the rectangular parallelepiped shape which satisfy | fills.
(Bz / Az) / (Bx / Ax) ≧ 1.27 (1)
(Bz / Az) / (By / Ay) ≧ 1.27 (2)
(However, “Ax” in the formula represents the longitudinal dimension of the foamable polymer, “Ay” in the formula represents the lateral dimension of the foamable polymer, and “Az” in the formula represents the foamable property. (Dimensions in the height direction of the polymer are shown.)   The acrylic monomer according to claim 1, wherein a polymerizable monomer containing 50 to 70% by mass of methyl methacrylate, 14 to 27% by mass of (meth) acrylic acid, and 10 to 30% by mass of styrene is used as the polymerizable monomer. Manufacturing method of resin foam.   Examples of the polymerizable monomer include methyl methacrylate 35 to 60% by mass, (meth) acrylic acid 14 to 35% by mass, styrene 10 to 20% by mass, maleic anhydride 1.0 to 10% by mass, and methacrylamide 1. The manufacturing method of the acrylic resin foam of Claim 1 using the polymerizable monomer containing 0-10 mass%. When the average bubble diameter in one direction is Hz, and the average bubble diameter in each of two directions orthogonal to the one direction and orthogonal to each other is Hx, Hy,
Hz / Hx is not less than 1.15, and state, and are Hz / Hy 1.17 or more,
A polymerizable solution containing a polymerizable monomer containing an acrylic monomer, a foaming agent containing a thermally decomposable foaming agent, and a polymerization initiator is prepared, and the polymerizable monomer is polymerized, and then obtained by the polymerization. Obtained by foaming a foamable polymer,
The polymerizable monomer is methyl methacrylate 50 to 70 wt%, (meth) 14 to 27 wt% acrylic acid, and acrylic resin foam characterized that you containing styrene 10 to 30 mass%. When the average bubble diameter in one direction is Hz, and the average bubble diameter in each of two directions orthogonal to the one direction and orthogonal to each other is Hx, Hy,
Hz / Hx is not less than 1.15, and state, and are Hz / Hy 1.17 or more,
A polymerizable solution containing a polymerizable monomer containing an acrylic monomer, a foaming agent containing a thermally decomposable foaming agent, and a polymerization initiator is prepared, and the polymerizable monomer is polymerized, and then obtained by the polymerization. Obtained by foaming a foamable polymer,
The polymerizable monomer is 35 to 60% by mass of methyl methacrylate, 14 to 35% by mass of (meth) acrylic acid, 10 to 20% by mass of styrene, 1.0 to 10% by mass of maleic anhydride, and methacrylamide. acrylic resin foam characterized that you containing 0 to 10% by weight. The acrylic resin foam according to claim 4 or 5 , wherein the average cell diameter is 0.3 to 1.3 mm. The acrylic resin foam according to any one of claims 4 to 6 , which has an apparent density of 0.03 to 0.15 g / cm ³ .