JP2014198795A - Method for manufacturing an acrylic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a foam unlikely to entail elongation defects at a foaming step, accompanied by scarce crude foam cells, and having a relatively homogeneous density.SOLUTION: The provided method for manufacturing an acrylic resin foam includes steps of forming, by using a foamable polymer and a molding mold, a foam by heating the foamable polymer housed within the molding mold, whereas the foam is prepared by executing, as these steps, a first step of forming, following the commencement of the foaming of the foamable polymer by heating the foamable polymer, a resin foam within a molding space and then enlarging the apparent volume of the foam in a state where the upper portion of the foam is being contacted with the ceiling wall of the molding mold and a second step of successively performing the heating within a molding space having a height greater than that of the molding space at the first step so as to enlarge the apparent volume of the foam.

Description

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

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.) to form a body of a car, a hull of a small boat, a wall material of a cold room of a freight vehicle, a wing of wind power generation, a table for an X-ray machine for transmitting X-rays, etc. It is used as a member.
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 rectangular parallelepiped foamable polymer is further added in a mold having a rectangular parallelepiped molding space. A method is employed in which urea is decomposed by heating to a high temperature to cause gas foaming.

JP 2006-045256 A

  However, the method of Patent Document 1 has a problem that density unevenness occurs in the resulting acrylic resin foam.

  Moreover, in the method of patent document 1, there exists a problem that elongation defect arises in a foaming step and the obtained acrylic resin foam may not be shape | molded according to a shaping | molding die.

Furthermore, the acrylic resin foam produced by the method of Patent Document 1 has a problem in that it may have larger coarse bubbles (for example, those having a bubble diameter of 5 mm or more) than the other bubbles.
For example, when an X-ray camera stand is made of an acrylic resin foam having such coarse bubbles, the coarse bubbles may appear as shadows on a photograph taken with the X-ray camera.
In addition, coarse bubbles in the acrylic resin foam may impair the aesthetics of the product made of the acrylic resin foam and may reduce the product value.
Furthermore, when adhering such an acrylic resin foam to another member (FRP or the like) via an adhesive, a large amount of the adhesive enters coarse bubbles, consuming the adhesive more than necessary, There is also a possibility of causing a problem that sufficient adhesive strength cannot be obtained.

  For such problems, no effective method has been found so far to suppress poor elongation at the foaming stage or to make it difficult for coarse bubbles and density unevenness to occur in the resulting acrylic resin foam. .

  In view of the above-described problems, the present invention provides a method for producing an acrylic resin foam that is capable of producing an acrylic resin foam that is less prone to elongation failure in the foaming stage, and that has fewer coarse bubbles and a relatively uniform density. It is an issue to provide.

The present inventors have intensively studied to solve the above problems, and have found the following, and have completed the present invention.
That is, in the conventional method for producing an acrylic resin foam, the foamable polymer formed in a plate shape, a molding space that can accommodate the foamable polymer, a bottom wall that defines the molding space, and A mold having a ceiling wall, and heat the foamable polymer placed on the bottom wall in the mold by the heated bottom wall and the ceiling wall. An acrylic resin foam is formed by heating above the decomposition temperature.
However, the lower surface of the foamable polymer in contact with the mold is heated before the upper surface, and in particular, the four corners of the lower surface of the foamable polymer are heated first. Foaming progresses in the vicinity of the four corners of the acrylic resin foam, and the acrylic resin foam is in a curved state with the central portion raised, and the upper portion is in contact with the mold and the lower portion is not in contact with the mold except in the vicinity of the four corners.
If the heating is further continued in this state, foaming progresses in the upper part than in the lower part, and the density in the upper part becomes lower than that in the lower part, resulting in uneven density in the resulting acrylic resin foam.
Further, when heating is further performed to promote foaming in the lower part, bubbles in the upper part are broken to generate coarse bubbles.
Furthermore, since the acrylic resin foam grows while it is curved, elongation failure occurs at the foaming stage.
Therefore, by suppressing the bending of the acrylic resin foam in the foaming stage, it is possible to produce an acrylic foam that is less prone to elongation in the foaming stage and that has few coarse bubbles and a relatively uniform density. The present invention has been found and the present invention has been completed.

That is, the present invention is a foamable polymer formed by dispersing a foaming agent containing a thermally decomposable foaming agent in a polymer obtained by polymerizing a polymerizable monomer containing an acrylic monomer, formed into a plate shape,
A molding die having a molding space capable of accommodating the foamable polymer, and having a bottom wall and a ceiling wall defining the molding space;
The foamable polymer placed on the bottom wall in the mold is heated above the thermal decomposition temperature of the pyrolyzable foaming agent by the heated bottom wall and ceiling wall, and an acrylic resin Comprising the step of forming a foam,
In the step, the foamable polymer is heated to a temperature equal to or higher than the thermal decomposition temperature of the pyrolyzable foaming agent to start foaming of the foamable polymer to form an acrylic resin foam in the molding space, A first step of increasing the apparent volume of the acrylic resin foam while bringing the upper part of the acrylic resin foam into contact with the ceiling wall of the mold;
A second step of further increasing the apparent volume of the acrylic resin foam by performing the heating in a molding space having a height higher than the molding space after the first step;
The method is for producing an acrylic resin foam.

  According to such a method for producing an acrylic resin foam, the upper part of the acrylic resin foam is brought into contact with the ceiling wall of the molding die whose inner dimension in the height direction is shorter than that of the molding die in the second step. By increasing the apparent volume of the acrylic resin foam, the acrylic resin foam can be prevented from being bent. Accordingly, it is possible to produce an acrylic resin foam that is less prone to elongation at the foaming stage, and has few coarse bubbles and a relatively uniform density.

  According to the present invention, there is provided a method for producing an acrylic resin foam that is capable of producing an acrylic resin foam that is less prone to elongation failure at the foaming stage, and that has few coarse bubbles and a relatively uniform density. Can do.

  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 formed into a plate shape, and a foaming agent containing a pyrolytic foaming agent is dispersed in a polymer obtained by polymerizing the polymerizable monomer.
Moreover, in the manufacturing method of the acrylic resin foam of this embodiment, it has the molding space which can accommodate the said foamable polymer and the said foamable polymer, and has the bottom wall and ceiling wall which define this molding space. The foamable polymer placed on the bottom wall in the mold is heated above the thermal decomposition temperature of the pyrolytic foaming agent by the heated bottom wall and the ceiling wall. The process of making it heat and forming an acrylic resin foam is implemented.
The bottom wall and the ceiling wall can be heated, for example, by placing the mold containing the foamable polymer in a heating furnace. Alternatively, the bottom wall and the ceiling wall can be heated by an electric heater or steam.

Specifically, in the step, the foamable polymer is heated to a temperature equal to or higher than the thermal decomposition temperature of the pyrolyzable foaming agent to start foaming of the foamable polymer, and the acrylic resin foam is formed in the molding space. A first step of increasing the apparent volume of the acrylic resin foam while bringing the upper part of the acrylic resin foam into contact with the ceiling wall of the mold, and after the first step The second step of further increasing the apparent volume of the acrylic resin foam by performing the heating in a molding space that is higher than the molding space.
The method for producing an acrylic resin foam according to the present embodiment is such that the upper part of the acrylic resin foam is brought into contact with the ceiling wall of the molding die whose inner dimension in the height direction is shorter than that of the molding die in the second step. By increasing the apparent volume of the acrylic resin foam, the acrylic resin foam can be prevented from being bent. Accordingly, it is possible to produce an acrylic resin foam that is less prone to elongation at the foaming stage, and has few coarse bubbles and a relatively uniform density.
In the step, as the mold used in the step, a mold formed so that the inner dimension in the height direction can be changed, and after performing the first step, the inner dimension in the height direction of the mold. And the second step is performed. Note that the first step and the second step may be continued after the second step.
The inner dimension in the height direction of the mold in the first step is preferably 1.2 to 5 times, and 2 to 4 times the dimension in the height direction of the foamable polymer. Is more preferable.
Further, the inner dimension in the height direction of the mold in the first step is preferably 0.1 to 0.9 times the inner dimension in the height direction of the mold in the second step, Moreover, it is more preferable that it is 0.5 to 0.9 times.
In addition, the shaping | molding die used at a 1st process and the shaping | molding die used at a 2nd process may be formed separately.

In the step, preferably, the molding space in the second step is a rectangular parallelepiped, and in the second step, the apparent volume of the acrylic resin foam is further increased in the mold. The acrylic resin foam is substantially filled to produce an acrylic resin foam having a shape corresponding to the molding space of the molding die, and the inside of the molding die in the vertical and horizontal directions in the second step. When the dimensions are Lm and Dm, respectively, the foamable polymer is a rectangular solid satisfying the following relational expression (1).
(1 / 1.30) ≦ (Lm / Lp) / (Dm / Dp) ≦ 1.30 (1)
(However, “Lp” in the formula represents the longitudinal dimension of the foamable polymer, and “Dp” in the formula represents the lateral dimension of the foamable polymer.)
In the manufacturing method of the acrylic resin foam of the present embodiment, when the inner dimensions in the vertical direction and the horizontal direction of the mold in the second step are Lm and Dm, respectively, the foamable polymer is related to the relationship. By forming a rectangular parallelepiped shape satisfying the formula (1), the acrylic resin foam can be stretched relatively uniformly in the vertical direction and the horizontal direction. An acrylic resin foam with a small amount can be produced.
In other words, when the relationship is deviated from the relational expression (1), the acrylic resin foam comes into contact with one of the longitudinal direction and the transverse direction of the mold at an early timing, and then the foam tries to extend to the other, so that the early timing A large frictional force is generated between the acrylic resin foam and the mold that are in contact with each other when the mold is stretched to the other side, and cannot be stretched uniformly.

  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 in the mold, the foamable polymer is formed at the center of the bottom wall of the molding space of the mold. It is preferable that the center of the bottom face be located.

  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 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 the method described in JIS K 7222: 2005 “Foamed Plastics and Rubber—How to Obtain the Apparent Density”.
That is, a test piece of 100 cm ³ or more was cut from a sample that had passed 72 hours or more after molding of the foam so as not to change the original bubble structure of the material, and the test piece was temperature 23 ± 2 ° C. and humidity 50 ± 5. %, Was allowed to stand for 16 hours or more, and then the mass of the test piece was measured and calculated according to the following formula.
Apparent density (kg / m ³ ) = Mass of test piece (g) / Volume of test piece (mm ³ ) × 10 ⁶

(Confirmation of presence of coarse bubbles in acrylic resin foam)
From the obtained acrylic resin foam, the skin part of the acrylic resin foam was removed, and a sample having a thickness of 25 mm × length of 200 mm × width of 200 mm was cut out. And this sample is divided into three by a slicer in the thickness direction, and two cross sections (one cross section of one cut location and one cross section of another cut location) (area of one cross section) : 200 mm × 200 mm), and the presence or absence of coarse bubbles of 5 mm or more was confirmed in the two cross sections. That is, the center of gravity of the cross-sectional shape of each bubble is obtained, the length of the longest portion of the straight distance passing through the center of gravity is defined as the bubble diameter (major axis), and the bubble diameter (major axis) is a bubble having a diameter of 5 mm or more. Presence or absence of coarse bubbles was confirmed as coarse bubbles.

(Confirmation of elongation at the four corners of the foam)
It was visually confirmed whether the obtained acrylic resin foam was formed according to the mold, that is, whether the four corners of the foam were sufficiently extended.

(Average bubble diameter)
About the acrylic resin foam, a 10 mm × 10 mm × 10 mm square was cut out so as to include an exposed cross section divided into three by a slicer in the thickness direction. Using a scanning electron microscope (“S-3000N” manufactured by Hitachi, Ltd.), the cut surface was photographed at a magnification of 18 times, and an image of the photographed cut surface was printed on A4 paper.
Next, six arbitrary line segments (length 60 mm) were drawn in the image obtained by photographing the cut surface, 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)
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)

Example 1
5 parts by mass of urea (thermal decomposition temperature: 135 ° 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, with respect to 100 parts by mass of the polymerizable monomer, 0.5 part 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 0.5 parts by mass of aniline, 0.04 parts by mass of hexatrimethylammonium chloride (“Nissan Cation PB-40R” manufactured by NOF Co., Ltd.) which is a surfactant as a substance for adding chloride ions, 0.6 mass of anhydrous sodium sulfate A portion was added to the monomer solution, and these were stirred to prepare a polymerizable solution.
37.5 kg of the polymerizable solution was placed in a rectangular parallelepiped mold having an internal method of 1800 mm (length) × 900 mm (width) × 25 mm (height) and formed of Teflon (registered trademark). And the foaming polymer (density: 1.15 g / cm < ³ >) was obtained by putting a polymeric solution into a thermostat with the formwork, and heating at 50 degreeC by nitrogen atmosphere for 10 hours. At this time, it was confirmed that the foamable polymer was cured.
Thereafter, the obtained foamable polymer was cut into the dimensions shown in Table 1, and placed in a mold as a molding die having an internal method of 2000 mm (length) × 1000 mm (width) × 65 mm (height), and the foamable polymer Were placed in a hot air circulating furnace at 170 ° C. (temperature higher than the temperature at which urea decomposes) together with the mold and foamed. After 30 minutes in the hot air circulation furnace, the foaming progressed in the vicinity of the four corners, and the acrylic resin foam was in a curved state with the central part raised. Next, the upper surface of the acrylic resin foam comes into contact with the ceiling wall of the mold and continues to foam in that state. After 1 hour and 30 minutes in the hot air circulation furnace, the lower surface of the acrylic resin foam becomes the mold. (The foaming process so far is the first process). Next, by raising the ceiling wall of the mold as the second step, the distance between the ceiling wall and the bottom wall is changed from 65 mm to 75 mm, and heating is further performed for 30 minutes, whereby an acrylic resin foam (apparent density: 0.051 g / cm ³ , average cell diameter: 0.50 mm).
The acrylic resin foam was white. The acrylic resin foam was a very good foam with no elongation failure at the four corners. Further, in the acrylic resin foam, coarse bubbles of 5 mm or more were not observed.
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 molding space of the mold.

(Example 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.
There was no poor elongation at the four corners of the acrylic resin foam, and the presence or absence of coarse bubbles of 5 mm or more was confirmed in the same manner as in Example 1, but no coarse bubbles of 5 mm or more were found.

(Example 3)
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.
There was no remarkable elongation failure at the four corners of the acrylic resin foam, and the presence or absence of coarse bubbles of 5 mm or more was confirmed in the same manner as in Example 1, but no coarse bubbles of 5 mm or more were found.

Example 4
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.
There was no remarkable elongation failure at the four corners of the acrylic resin foam, and the presence or absence of coarse bubbles of 5 mm or more was confirmed in the same manner as in Example 1, but no coarse bubbles of 5 mm or more were found.

(Comparative Example 1)
Regarding the dimensions of the mold, an acrylic resin foam was obtained in the same manner as in Example 2 except that the height of the inner dimension of the mold in the first step was 75 mm.
There were significant elongation defects at the four corners of the acrylic resin foam. When the presence or absence of coarse bubbles of 5 mm or more was confirmed in the same manner as in Example 1, many coarse bubbles of 5 mm or more were observed.

  The test results are shown in Table 1.

As shown in Table 1, in the acrylic resin foams of Examples 1 to 4, the number of coarse bubbles of 5 mm or more was zero. In addition, the acrylic resin foams of Examples 1 to 4 had better elongation at the four corners of the foam than Comparative Example 1.
In particular, the acrylic resin foams of Examples 1 and 2 prepared with (Lm / Lp) / (Dm / Dp) in the range of (1 / 1.30) to 1.30 are the four corners of the foam. The elongation state of was very good.

Claims (3)

A foamable polymer in which a foaming agent containing a thermally decomposable foaming agent is dispersed in a polymer obtained by polymerizing a polymerizable monomer containing an acrylic monomer;
A molding die having a molding space capable of accommodating the foamable polymer, and having a bottom wall and a ceiling wall defining the molding space;
The foamable polymer placed on the bottom wall in the mold is heated above the thermal decomposition temperature of the pyrolyzable foaming agent by the heated bottom wall and ceiling wall, and an acrylic resin Comprising the step of forming a foam,
In the step, the foamable polymer is heated to a temperature equal to or higher than the thermal decomposition temperature of the pyrolyzable foaming agent to start foaming of the foamable polymer to form an acrylic resin foam in the molding space, A first step of increasing the apparent volume of the acrylic resin foam while bringing the upper part of the acrylic resin foam into contact with the ceiling wall of the mold;
A second step of further increasing the apparent volume of the acrylic resin foam by performing the heating in a molding space having a height higher than the molding space after the first step;
The manufacturing method of the acrylic resin foam characterized by implementing. The molding space in the second step is a rectangular parallelepiped shape,
In the second step, by further increasing the apparent volume of the acrylic resin foam, the acrylic resin foam is substantially filled in the mold, and the shape corresponding to the molding space of the mold Acrylic resin foam having
The foamable polymer is a rectangular parallelepiped that satisfies the following relational expression (1) when the inner dimensions in the vertical direction and the horizontal direction of the mold in the second step are Lm and Dm, respectively. Manufacturing method of acrylic resin foam.
(1 / 1.30) ≦ (Lm / Lp) / (Dm / Dp) ≦ 1.30 (1)
(However, “Lp” in the formula represents the longitudinal dimension of the foamable polymer, and “Dp” in the formula represents the lateral dimension of the foamable polymer.)   The polymerizable monomer according to claim 1 or 2, 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. A method for producing an acrylic resin foam.