JP5906119B2 - 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, 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 a wall material for a cold storage room of a cargo vehicle, a hull of a small boat, a wing of wind power generation, and the like. In addition, taking advantage of its light resistance, it is also used as a member for constituting a table for an X-ray machine for transmitting X-rays, a lighting heat insulating plate and the like.
Such an acrylic resin foam is usually prepared by preparing a polymerizable solution in which urea as a foaming agent and a polymerization initiator are mixed with an acrylic monomer, as shown in Patent Document 1 below. After pouring the functional 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 and cause gas foaming. The method is adopted.

JP 2006-045256 A

  However, when an acrylic resin foam is used for a daylighting insulation board or the like, a light transmission property higher than that of an acrylic resin foam obtained by a conventional method is demanded. No effective method has been found for further improving the light transmission, and it is difficult to increase the light transmittance.

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

  The present inventors have intensively studied to solve the above-mentioned problems, and by making the average cell diameter of the acrylic resin foam 1.2 mm or more, the acrylic resin foam has excellent light transmittance. As a result, the present invention has been found.

  That is, the present invention is an acrylic resin foam characterized by having an average cell diameter of 1.2 mm or more.

  Further, the present invention contains a polymerizable monomer containing an acrylic monomer, a foaming agent containing urea, and a polymerization initiator, and further contains an alcohol having a boiling point of 70 ° C. or more and less than 180 ° C. as the foaming agent. After preparing the polymerizable solution to be polymerized and polymerizing the polymerizable monomer, the foamable polymer obtained by the polymerization is foamed to produce an acrylic resin foam having an average cell diameter of 1.2 mm or more. The present invention provides a method for producing an acrylic resin foam.

  According to this invention, it can be set as the acrylic resin foam excellent in the light transmittance by making the average cell diameter of an acrylic resin foam into 1.2 mm or more.

The SEM photograph of the section of the acrylic resin foam of an example. The SEM photograph of the section of the acrylic resin foam of a comparative example.

  Embodiments of the present invention will be described below.

The method for producing an acrylic resin foam of the present embodiment comprises a polymerizable monomer containing an acrylic monomer, urea, a foaming agent containing an alcohol having a boiling point of 70 ° C. or higher and less than 180 ° C., and a polymerization initiator. A polymerizable solution preparation step for preparing a polymerizable solution containing, a foamable polymer preparation step for preparing a foamable polymer by polymerizing the polymerizable monomer by heating the polymerizable solution, and the foamability And a foam production step of producing an acrylic resin foam having an average cell diameter of 1.2 mm or more by foaming a polymer.
Hereinafter, first, components of the polymerizable solution will be described.

(Acrylic monomer)
As the acrylic monomer, a water-soluble acrylic monomer is preferably contained, and (meth) acrylic acid is preferably used, since it exhibits excellent solubility in urea used as a foaming agent.
In this specification, the term “(meth) acryl” means either “methacryl” or “acryl”.
In addition, as the acrylic monomer other than (meth) acrylic acid, it is preferable to use methyl methacrylate because it can exhibit excellent foamability when foaming the foamable polymer of the acrylic monomer.
Examples of acrylic monomers other than (meth) acrylic acid and methyl methacrylate include maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, crotonic acid, methyl acrylate, ethyl (meth) acrylate, (meth ) Butyl acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, (meth) acrylamide, maleate amide, maleate imide, etc. can do.

(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 total of the polymerizable monomers is preferably 20% by mass or less.

More specifically, in the polymerizable solution in the present embodiment, 35 to 60% by mass of the polymerizable monomer contained is methyl methacrylate, 14 to 35% by mass is (meth) acrylic acid, It is preferable that 20% by mass is styrene.
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, from the viewpoint of solubility in urea, it is preferable to contain a large amount of methacrylic acid.
By adopting such a blend, an acrylic resin foam excellent in foamability, hard and excellent in strength can be obtained.

(Foaming agent)
As the foaming agent, a foaming agent containing a pyrolytic foaming agent containing urea and an alcohol having a boiling point of 70 ° C. or higher and lower than 180 ° C. is used.
If the urea content is low, the foaming degree of the resulting acrylic resin foam may be reduced and the lightness may be impaired. Conversely, if it is excessive, urea is uniformly dissolved in the polymerizable solution. There is a risk that it may be difficult to cause the urea to remain in the resulting acrylic resin foam or to cause bubble breakage.
Therefore, urea is preferably contained in the polymerizable solution at a ratio of 0.5 to 15 parts by mass when the total amount of polymerizable monomers is 100 parts by mass, and 0.6 to 10 parts by mass. It is more preferable to make it contain in a polymerizable solution in the ratio used as a part.
Examples of the thermally decomposable foaming agent other than urea include urea derivatives, dinitrosopentamethylenetetramine, amidoguanidine, trimethylenetriamine, paratoluenesulfone hydrazine, azodicarbonamide, thiourea, ammonium chloride, dicyandiamide, dioxane, hexane, Water chloral, citric acid and the like can be mentioned.
The thermal decomposable foaming agent other than urea may or may not be used. However, if the amount used is large, it may be difficult to uniformly dissolve the thermal decomposable foaming agent in the polymerizable solution. There is a risk that the pyrolytic foaming agent may easily remain in the resulting acrylic resin foam or foam breakage may occur. The thermally decomposable foaming agent other than urea can be contained in the polymerizable solution at a ratio of 0 to 5 parts by mass when the total amount of polymerizable monomers is 100 parts by mass.
Examples of the alcohol having a boiling point of 70 ° C. or higher and lower than 180 ° C. include ethanol, isopropanol, cyclopentanol, 1-propanol, 2-methyl-2-propanol, and t-butanol. The alcohol is not effective even when used alone, and is effective when used in combination with urea.
When the amount of the alcohol used is small, the effect of increasing the bubble diameter and the effect of decreasing the density are small, and if the amount is too large, the polymerization reaction is difficult to proceed. Therefore, the total amount of the polymerizable monomers is 100 parts by mass. It is preferable to make it contain in a polymerizable solution in the ratio used as 0.1-15 mass parts, and it is more preferable to make it contain in a polymerizable solution in the ratio used as 0.5-12 mass parts. More preferably, it is contained in the polymerizable solution at a ratio of parts. Moreover, it is preferable to make it contain in a polymeric solution in the ratio used as 0.1-500 mass parts of alcohol with respect to 100 mass parts of urea as a use ratio of urea and alcohol, and the ratio used as 1-400 mass parts. More preferably, it is contained in the polymerizable solution.

(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 and the like. Use.
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.
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 resulting acrylic resin foam may be reduced, or the bubbles of the acrylic resin foam may be coarse. Therefore, when the total amount of polymerizable monomers is 100 parts by mass, it is preferably contained in the polymerizable solution at a ratio of 0.5 to 20 parts by mass, and 0.6 to 10 parts by mass. Is more preferable, and 0.7 to 5 parts by mass is particularly preferable.

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

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

(Foam production process)
The foam preparation step is a step of forming the acrylic resin foam by decomposing the urea by heating the foamable polymer at a temperature equal to or higher than the temperature at which the urea decomposes.
The temperature at which the foamable polymer is heated is preferably a temperature equal to or higher than the boiling point of the alcohol to be used (the boiling point of the alcohol having the highest boiling point when a plurality of types of alcohols are used). Higher temperatures are preferred. The upper limit of this heating temperature is about 200 ° C. If it exceeds 200 ° C., the acrylic resin foam may shrink due to heat.

According to the method for producing an acrylic resin foam of the present embodiment, a polymerizable monomer containing an acrylic monomer, urea, a foaming agent containing an alcohol having a boiling point of 70 ° C. or higher and lower than 180 ° C., and a polymerization initiator To obtain an acrylic resin foam having a large average cell diameter by foaming the foamable polymer obtained by the polymerization, after polymerizing the polymerizable monomer. Can do. The obtained acrylic resin foam has an advantage that light transmittance is improved due to the large average cell diameter.
Moreover, according to the manufacturing method of the acrylic resin foam of this embodiment, the acrylic resin foam with a small dispersion | variation in a bubble diameter can be obtained. Since the obtained acrylic resin foam has a small variation in cell diameter, the aesthetics of the product composed of the acrylic resin foam become excellent, and the product value can be improved.

Next, the acrylic resin foam according to this embodiment will be described.
The acrylic resin foam according to the present embodiment has an average cell diameter of 1.2 mm or more, preferably 1.2 to 2.5 mm, more preferably 1.4 to 2.0 mm. Light transmittance is excellent due to the large average cell diameter. If it is too large, the workability may deteriorate.
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.

Further, the acrylic resin foam according to the present embodiment has a standard deviation of the bubble diameter of preferably less than 25%, more preferably less than 20%.
The standard deviation of the bubble diameter is calculated as follows.
That is, the acrylic resin foam is cut, and the cross section (bubble wall portion) of the foam is dyed with ink for the portion excluding the outside 1/10 in the cut surface thickness direction. Then, the dyed cross section is photographed with a magnification of 20 times using a microscope. Using the obtained image, 100 or more independent bubble diameters that can be confirmed in the visual field are measured. When 100 independent bubbles that can be confirmed in the visual field cannot be obtained, the number of possible bubbles is measured. The bubble diameter is obtained by obtaining the center of the cross-sectional shape of the bubble and measuring the longest portion of the straight line distance passing through the center. And the standard deviation of the bubble diameter of the said acrylic resin foam is computed from the calculated | required bubble diameter.

  Furthermore, the acrylic resin foam according to the present embodiment preferably contains a polymerizable monomer containing an acrylic monomer, a foaming agent containing urea, and a polymerization initiator, and further has a boiling point as the foaming agent. An acrylic resin foam obtained by preparing a polymerizable solution containing an alcohol having a temperature of 70 ° C. or higher and lower than 180 ° C., polymerizing the polymerizable monomer, and then foaming the foamable polymer obtained by the polymerization. It is.

  Moreover, the acrylic resin foam according to the present embodiment preferably has a plate shape. Moreover, when the acrylic resin foam according to the present embodiment has a plate shape, the total light transmittance in the thickness direction is preferably 25% or more, more preferably 28% or more. The total light transmittance is measured according to JIS K 7361-1: 1997.

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. More preferably, it is 10 g / cm ³ or less. 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 )

  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 an acrylic resin foam will be described.

(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 )

(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.

(Standard deviation of cell diameter of acrylic resin foam)
The acrylic resin foam was cut, and the cross section (bubble wall portion) of the foam was dyed with ink for the portion excluding the outside 1/10 in the cut surface thickness direction. Then, the stained cross section was photographed with a magnification of 20 times using a microscope ("VHX-1000" manufactured by Keyence Corporation). Using the obtained image, 100 bubble diameters of independent bubbles that can be confirmed in the visual field were measured. In addition, the bubble diameter was calculated | required by calculating | requiring the longest part by the linear distance which passes along the center and calculated | requires the center of the cross-sectional shape of a bubble.
And the standard deviation of the bubble diameter of the said acrylic resin foam was computed from the calculated | required bubble diameter.

(Total light transmittance of acrylic resin foam)
The total light transmittance of the acrylic resin foam was measured according to JIS K 7361-1: 1997. As a measurement sample, five test pieces having a thickness of 10 mm, a length of 100 mm, and a width of 100 mm were cut out from the obtained acrylic resin foam so as not to include the skin, and the 10 mm-thick acrylic resin foam was measured in the thickness direction. The total light transmittance was measured. As a measuring apparatus, Heze-meter HM-150 (Murakami Color Research Laboratory Co., Ltd.) was used. The arithmetic average of the measured values of the five test pieces was defined as the total light transmittance of the foam.

(Example 1: Preparation of polymerizable solution)
For 100 parts by mass of a polymerizable monomer consisting of 60% by mass of methyl methacrylate, 25% by mass of methacrylic acid, and 15% by mass of styrene, t-butyl hydroperoxide (“Perbutyl H” manufactured by NOF Corporation). -69 ") 0.5 parts by mass, 0.5 parts by mass of N, N-dimethylaniline as a reducing agent, cetyltrimethylammonium chloride as a substance for adding chloride ions (" Nissan Cation PB-40R "manufactured by NOF Corporation) ) 0.04 parts by mass, 5 parts by mass of urea as a blowing agent, and 2 parts by mass of isopropanol (boiling point: 82.4 ° C.) as a blowing agent were mixed and stirred uniformly to prepare a polymerizable solution.

(Example 1: Production of expandable polymer)
800 g of the polymerizable solution of Example 1 was placed in a glass cuboid mold having an inner method of 2.5 cm × 12 cm × 30 cm.
And the foaming polymer was produced by putting the polymerizable solution into the thermostat together with the mold and heating at 50 ° C. for 10 hours.

(Example 1: Production of acrylic resin foam)
The foamable polymer of Example 1 was placed in a foaming mold, and the foamable polymer was heated together with the foaming mold at 170 ° C. for 50 minutes to prepare an acrylic resin foam. This acrylic resin foam has an apparent density of 0.047 g / cm ³ , an average cell diameter of 1.42 mm, a standard deviation of the cell diameter of 19.4%, and a total light transmittance of 28. 3%.

(Example 2: Preparation of polymerizable solution)
A polymerizable solution was prepared in the same manner as in Example 1 except that ethanol (boiling point: 78.4 ° C.) was used instead of isopropanol, and 4 parts by mass of ethanol was mixed with 100 parts by mass of the polymerizable monomer. did.

(Example 2: Production of foamable polymer)
A foamable polymer was produced in the same manner as in Example 1 except that the polymerizable solution of Example 2 was used instead of the polymerizable solution of Example 1.

(Example 2: Production of acrylic resin foam)
An acrylic resin foam was produced in the same manner as in Example 1, except that the foamable polymer of Example 2 was used instead of the foamable polymer of Example 1. This acrylic resin foam has an apparent density of 0.047 g / cm ³ , an average cell diameter of 1.46 mm, a standard deviation of the cell diameter of 19.0%, and a total light transmittance of 28. 7%.

(Example 3: Preparation of polymerizable solution)
A polymerizable solution was prepared in the same manner as in Example 1 except that 8 parts by mass of isopropanol and 2.5 parts by mass of urea were mixed with 100 parts by mass of the polymerizable monomer.

(Example 3: Production of foamable polymer)
A foamable polymer was produced in the same manner as in Example 1 except that the polymerizable solution in Example 3 was used instead of the polymerizable solution in Example 1.

(Example 3: Production of acrylic resin foam)
An acrylic resin foam was produced in the same manner as in Example 1, except that the foamable polymer of Example 3 was used instead of the foamable polymer of Example 1. This acrylic resin foam has an apparent density of 0.047 g / cm ³ , an average cell diameter of 1.79 mm, a standard deviation of the cell diameter of 18.6%, and a total light transmittance of 29. 0%.

(Comparative Example 1: Preparation of polymerizable solution)
A polymerizable solution was prepared in the same manner as in Example 1 except that isopropanol was not used and 7 parts by mass of urea was mixed with 100 parts by mass of the polymerizable monomer.

(Comparative Example 1: Production of foamable polymer)
A foamable polymer was 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.

(Comparative Example 1: Production of acrylic resin foam)
An acrylic resin foam was produced in the same manner as in Example 1 except that the foamable polymer of Comparative Example 1 was used instead of the foamable polymer of Example 1. This acrylic resin foam has an apparent density of 0.047 g / cm ³ , an average cell diameter of 0.86 mm, a standard deviation of the cell diameter of 25.8%, and a total light transmittance of 23. 0%.

The test results are shown in Table 1. In addition, in Table 1, description of the compounding quantity common to all the Examples and the comparative examples is omitted.
Moreover, the SEM photograph of the cross section of the acrylic resin foam of an Example is shown in FIG. 1, and the SEM photograph of the cross section of the acrylic resin foam of a comparative example is shown in FIG.

As shown in Table 1, the acrylic resin foams of Examples 1 to 3 within the scope of the present invention are compared to the acrylic resin foam of Comparative Example 1 having an average cell diameter of 0.86 mm. The total light transmittance was high.
Therefore, according to this invention, it turns out that the acrylic resin foam excellent in the light transmittance can be provided.
Moreover, as shown in Table 1, the acrylic resin foams of Examples 1 to 3 within the scope of the present invention were compared with the acrylic resin foam of Comparative Example 1 prepared without using alcohol. The standard deviation of the bubble diameter was low.
Therefore, according to this invention, it turns out that the acrylic resin foam with a small dispersion | variation in a bubble diameter can be provided.

Claims (5)

Ri Der average bubble diameter of 1.2mm or more,
A polymerizable solution containing a polymerizable monomer containing an acrylic monomer, a foaming agent containing urea, and a polymerization initiator, and further containing, as the foaming agent, an alcohol having a boiling point of 70 ° C. or higher and lower than 180 ° C. is prepared. An acrylic resin foam obtained by polymerizing the polymerizable monomer and then foaming the foamable polymer obtained by the polymerization .   The acrylic resin foam according to claim 1, wherein the standard deviation of the bubble diameter is less than 25%. The acrylic resin foam according to claim 1 or 2 , wherein the polymerizable monomer contains 35 to 60% by mass of methyl methacrylate, 14 to 35% by mass of (meth) acrylic acid, and 10 to 20% by mass of styrene. . The acrylic resin foam according to any one of claims 1 to 3 , which has a plate shape and has a total light transmittance in a thickness direction of 25% or more.   A polymerizable solution containing a polymerizable monomer containing an acrylic monomer, a foaming agent containing urea, and a polymerization initiator, and further containing, as the foaming agent, an alcohol having a boiling point of 70 ° C. or higher and lower than 180 ° C. is prepared. Then, after polymerizing the polymerizable monomer, the foamable polymer obtained by the polymerization is foamed to produce an acrylic resin foam having an average cell diameter of 1.2 mm or more. A method for producing an acrylic resin foam.