JP5957252B2 - Method for producing acrylic resin foam - Google Patents

Description

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

Conventionally, acrylic resin foam has excellent strength, light weight, heat insulation, and light transmission. Therefore, wind power wings, freight vehicle cold room wall materials, small boat hulls, X It is used as a member for constituting an X-ray machine stand for transmitting a line.
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, in the conventional method for producing an acrylic resin foam, a long reaction time is required from the start of polymerization of an acrylic monomer until the foam is obtained. For example, Example 1 of Patent Document 1 Then, after carrying out the reaction for 10 hours, the temperature is further raised to carry out an additional reaction for 3 hours, and the acrylic resin foam is completed by polymerizing acrylic monomers over a total of 13 hours. I am letting.
For such a problem, an effective method for accelerating the reaction of a polymerizable monomer component including an acrylic monomer has not been found so far, and the production efficiency of an acrylic resin foam can be improved. It is a difficult situation.

In addition, the acrylic resin foam produced by the method of Patent Document 1 has larger large bubbles (hereinafter also referred to as “voids”) that protrude than other bubbles (for example, those having a bubble diameter of 2 mm or more). There is.
For example, when an X-ray camera stand is made of an acrylic resin foam having such voids, voids may appear as shadows on photographs taken with the X-ray camera.
In addition, when such an acrylic resin foam is bonded to another member via an adhesive, a large amount of the adhesive enters the void, and the adhesive is consumed more than necessary or sufficient adhesive strength is obtained. There is also a possibility of causing a problem that it cannot be obtained.
Furthermore, the voids in the acrylic resin foam may impair the aesthetics of the product composed of the acrylic resin foam and may reduce the product value.
Conventionally, no effective method has been found to make it difficult for voids to occur, and it is difficult to make voids difficult to generate.

  In view of the above problems, the present invention provides a method for producing an acrylic resin foam capable of efficiently producing an acrylic resin foam and making it difficult for voids to form in the acrylic resin foam. Let it be an issue.

The present inventors have intensively studied to solve the above problems, and in the conventional method for producing an acrylic resin foam, moisture is contained in the polymerizable solution, and this moisture requires time for polymerization. It was found to be one of the causes and one of the causes of voids. The reason why the polymerizable solution contains water is that the raw material of the polymerizable solution contains hygroscopic material (acrylic monomer, etc.), and water originally contains water (hydrophilic polymerization initiator, etc.). This is considered to be one of the causes.
In addition, the present inventors prepared a polymerizable solution having a moisture content of 2% by mass or less, and polymerized the polymerizable monomer component in the polymerizable solution by heating, thereby promoting the polymerization reaction of the polymerizable monomer component. I found out that I can make it. And the present inventors discovered that an acrylic resin foam can be produced in a short time compared with the past by accelerating the polymerization reaction of a polymerizable monomer component.
Furthermore, the present inventors prepared a polymerizable solution having a water content of 2% by mass or less, and polymerized the polymerizable monomer component in the polymerizable solution by heating, whereby a void was formed in the acrylic resin foam. It was found that it can be made difficult to occur.
And the present inventors have come to complete this invention by discovering these.

  That is, in the present invention, the polymerizable monomer component containing an acrylic monomer, the foaming agent containing urea, and the polymerization solution containing the polymerization initiator are heated to polymerize the polymerizable monomer component, A method for producing an acrylic resin foam, wherein the foamable polymer obtained by polymerization is foamed by heating to form an acrylic resin foam, wherein the water content is 2% by mass or less. It is in the manufacturing method of the acrylic resin foam characterized by implementing the said polymerization by heating.

According to the present invention, the polymerization reaction of the polymerizable monomer component can be promoted by carrying out the polymerization by heating the polymerizable solution having a water content of 2% by mass or less. The resin foam can be produced in a shorter time than the conventional method.
Moreover, according to this invention, a void can be made hard to produce in an acrylic resin foam by implementing the said polymerization by heating the said polymeric solution whose moisture content is 2 mass% or less. Voids can be made less likely to be produced by preventing the dispersion of urea in the foaming polymerization solution or by decomposing and foaming urea as a foaming agent by making the water content of the polymerizable solution 2% by mass or less. As a result, urea is relatively uniformly dispersed in the foaming polymerization solution, and the added urea is relatively uniformly decomposed and foamed in the foaming polymer. It is believed that there is.
Therefore, according to this invention, an acrylic resin foam can be manufactured efficiently and it can be made hard to produce a void in an acrylic resin foam.

  Hereinafter, a dehydrating agent is added to and mixed with the raw material of the polymerizable solution to prepare a mixture. After removing water from the mixture, the dehydrating agent is removed from the mixture by filtration, and the water content is 2% by mass or less. An embodiment of the present invention will be described with reference to an example of producing a polymerizable solution.

The method for producing an acrylic resin foam according to this embodiment includes a polymerizable solution preparation step of preparing a polymerizable solution containing a polymerizable monomer component containing an acrylic monomer, a foaming agent containing urea, and a polymerization initiator. A foamable polymer preparation step of preparing the foamable polymer by polymerizing the polymerizable monomer component by heating the polymerizable solution below the thermal decomposition temperature of urea, and the foamable polymer of urea. And a foam production step of decomposing the urea by heating at a thermal decomposition temperature or higher to form an acrylic resin foam.
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. Among these, it is preferable that maleic anhydride and methacrylamide are contained in the polymerizable solution from the viewpoint that high heat resistance can be imparted to the resulting acrylic resin foam.

(Polymerizable monomer components other than acrylic monomers)
In addition, as a polymerizable monomer component 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 of the acrylic resin foam molded article may be impaired, so the content of the styrene monomer in the total of the polymerizable monomer components is 20% by mass or less. It is preferable.

More specifically, in the polymerizable solution in the present embodiment, 35 to 70% by mass of the polymerizable monomer component contained is methyl methacrylate, 14 to 45% by mass is (meth) acrylic acid, 10 It is preferable that -20 mass% is styrene.
In addition, all (meth) acrylic acid contained in the ratio of 14-45 mass% may be methacrylic acid, all may be acrylic acid, and 14-45 combining both methacrylic acid and acrylic acid. 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.

(urea)
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.
For these reasons, urea is preferably contained in the polymerizable solution at a ratio of 1 to 15 parts by mass when the total amount of the polymerizable monomer components is 100 parts by mass.

(Foaming agents other than urea)
As the foaming agent other than urea, a pyrolytic foaming agent other than urea can be used.
The pyrolyzable foaming agent decomposes at 65 ° C. or higher to generate gas, and preferably decomposes at 100 to 180 ° C. to generate gas.
Examples of the thermally decomposable foaming agent other than urea include urea derivatives, dinitrosopentamethylenetetramine, amidoguanidine, trimethylenetriamine, paratoluenesulfone hydrazine, azodicarbonamide, thiourea, ammonium chloride, dicyandiamide, dioxane, hexane, Examples include water chloral and citric acid.
Further, other foaming agents other than the pyrolytic foaming agent can be used. 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. preferable. Specific examples include alcohols such as isopropanol, cyclopentanol, ethanol, 1-propanol, 2-methyl-2-propanol, and 2-ethyl-1-hexanol.
As a use amount of the blowing agent other than urea, when the total amount of the polymerizable monomer components is 100 parts by mass, the total amount with the urea is included in the polymerizable solution in a ratio of 1.1 to 30 parts by mass. It is preferable.

(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, the former redox polymerization initiator, for example, hydrophilic t-butyl hydroper It is preferable to use oxide.
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 monomers is 100 parts by mass.

(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 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.
In addition, the metal ion exhibits a function as an electron-donating substance, that is, an oxidizing agent, or an electron-donating substance, that is, a reducing agent, in a polymerizable solution, and the polymerization reaction of the polymerizable monomer component. It contributes to promotion.
On the other hand, the chloride ion contributes to the promotion of the polymerization reaction of the polymerizable monomer component 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, a ratio of 0.005 to 5 parts by mass when the total amount of the polymerizable monomer components in the polymerizable solution is 100 parts by mass. It can be made to contain.

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 monomer components in the polymerizable solution is 100 parts by mass. It can be made to contain.

(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 which will be 0.001-5 mass parts, for example, when the total amount of the polymerizable monomer component in a polymeric solution is 100 mass parts. By containing the polymerization inhibitor, the polymerizable solution is advantageous in that it can suppress excessive polymerization when the polymerizable monomer component 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, diatomaceous earth, sodium sulfate, adipic acid ester, phthalic acid ester, and citric acid ester.
The content of such a bubble regulator in the polymerizable solution is, for example, contained in a ratio of 0.01 to 10 parts by mass when the total amount of the polymerizable monomer components in the polymerizable solution is 100 parts by mass. be able to.

(Acrylic resin foam)
In the present embodiment, the polymerizable solution may further contain an acrylic resin foam obtained by foaming a foamable polymer having the same or different polymerizable monomer component as the polymerizable monomer component. .
The acrylic resin foam contributes to the acceleration of the polymerization reaction of the polymerizable monomer component 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 when the total amount of polymerizable monomer components in the polymerizable solution is 100 parts by mass, More 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 monomer components, the acrylic resin foam is uniformly formed into a polymerizable monomer component. There is an advantage that it is easily dissolved. In addition, the polymerizable solution is such that the acrylic resin foam is 0.1 part by mass or more with respect to 100 parts by mass of the total amount of the polymerizable monomer component, so that the polymerizable monomer component in the polymerizable solution There is an advantage that polymerization is accelerated.

(Polymerizable solution preparation process)
In the polymerizable solution preparation step of the method for producing an acrylic resin foam according to the present embodiment, the above-described materials are mixed to prepare a polymerizable solution. At this time, the polymerizable solution usually contains water in a proportion exceeding 2% by mass. Therefore, the polymerizable solution and the dehydrating agent are mixed to prepare a mixture, and moisture is removed from the polymerizable solution. Remove. Thereafter, the dehydrating agent is removed from the mixture by filtration to prepare a polymerizable solution having a water content of 2% by mass or less. A polymerizable solution having a water content of 1% by mass or less is preferable.
As the dehydrating agent, zeolite (such as molecular sieve) can be preferably used. If the content in the mixture of the dehydrating agent is small, the dehydrating effect is insufficient, and even if it is large, the dehydrating effect reaches its peak and post-treatment becomes difficult. Therefore, the total amount of the polymerizable monomer components in the polymerizable solution is 100 parts by mass. It is preferable to make it contain in the ratio used as 0.01-50 mass parts.
In the present embodiment, even when a polymerizable solution having a water content exceeding 2% by mass is produced, the water content of the polymerizable solution can be reduced to 2% by mass or less by the dehydrating agent. Therefore, in order to prevent moisture absorption of the monomer and adhesion of moisture in the raw material transport path, there is no need to strictly manage the raw material and equipment, and the polymerization reaction of the polymerizable monomer component can be promoted. As a result, the acrylic resin foam can be produced in a shorter time than the conventional method. In addition, an acrylic resin foam having no voids or few voids can be produced by a simple method.

(Foaming polymer production process)
In the foaming polymer preparation step, a polymerizable solution having a water content of 2% by mass or less is placed in a mold and heated at a temperature higher than the temperature at which the polymerizable monomer component is polymerized and lower than the temperature at which the urea is decomposed. This is a step of polymerizing the polymerizable monomer component of the polymerizable solution to produce a foamable polymer. In the foamable polymer production step, it is preferable to use a polymerizable solution having a water content of 1% by mass or less as the polymerizable solution to be put into the mold.
Specifically, in the foamable polymer preparation step, an atmosphere at a temperature equal to or higher than a temperature at which the polymerizable monomer component is polymerized and lower than a temperature at which the urea is decomposed is used. A heating step for heating until just before the polymerization of the polymerizable monomer component, and a temperature at which the polymerizable monomer component polymerizes the polymerizable solution immediately before the polymerization of the polymerizable monomer component, and the urea decomposes A polymerization step of polymerizing the polymerizable monomer component to form a foamable polymer by further heating at a temperature lower than the temperature.
About the amount of moisture, the amount of moisture contained in the polymerizable solution immediately before the heating step may be 2% by mass or less. If the amount of water contained in the polymerizable solution immediately before the heating step is 2% by mass or less, the amount of water contained in the polymerizable solution is further reduced by the heating step, and the polymerization step Sometimes, the amount of water contained in the polymerizable solution is lower than immediately before the heating step is performed. Moreover, when the process of polymerizing the polymerizable monomer component of the polymerizable solution is performed in an inert gas (nitrogen gas, argon gas, etc.) atmosphere, moisture absorption of the monomer can be further suppressed.
The water content means a value measured by the Karl Fischer titration method (direct titration method).

(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.
Before the foam production step, the foamable polymer is heated below the temperature at which the urea decomposes to vaporize water contained in the foamable polymer to reduce the water content of the foamable polymer. Also good. Thereby, in the said foam preparation process, the foamable polymer with which the moisture content was reduced will be used, and there exists an advantage that a void becomes much less likely to arise in an acrylic resin foam.

Since the manufacturing method of the acrylic resin foam according to the present embodiment is configured as described above, it has the following advantages.
That is, in the method for producing an acrylic resin foam according to this embodiment, the polymerization reaction of the polymerizable monomer component can be promoted by heating the polymerizable solution having a moisture content of 2% by mass or less. As a result, the acrylic resin foam can be produced in a shorter time than the conventional method.
Moreover, in the manufacturing method of the acrylic resin foam which concerns on this embodiment, it can make it difficult to produce a void in an acrylic resin foam by heating the said polymeric solution whose water content is 2 mass% or less. . Voids can be made less likely to be produced by reducing the water content of the polymerizable solution to 2% by mass or less, thereby preventing the dispersion of urea in the foaming polymerization solution and the possibility of preventing decomposition foaming. By reducing the amount, it is considered that the added urea decomposes and foams relatively uniformly in the foamable polymer.
Therefore, according to the method for producing an acrylic resin foam according to the present embodiment, the acrylic resin foam can be efficiently produced, and voids can be hardly generated in the acrylic resin foam.

  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.

(Example 1: Preparation of polymerizable solution)
5 parts by mass of urea (thermal decomposition temperature: 135 ° C.) as a blowing agent is mixed with 100 parts by mass of a polymerizable monomer component consisting of 61% by mass of methyl methacrylate, 24% by mass of methacrylic acid, and 15% by mass of styrene. In addition, the monomer solution was prepared by uniformly dissolving.
And 100 parts by mass of the polymerizable monomer component, 0.5 parts by mass of t-butyl hydroperoxide (“Perbutyl H-69” manufactured by NOF Corporation) as a polymerization initiator, N, N— as a reducing agent 0.5 parts by mass of dimethylaniline, 0.04 parts by mass of hexatrimethylammonium chloride (“Nissan Cation PB-40R” manufactured by NOF Corporation) as a surfactant as a substance for adding chloride ions, metal ions (Cu ²⁺ ) As a substance for addition, 5.9 × 10 ⁻⁷ parts by mass of copper stearate (manufactured by Mitsuwa Chemical Co., Ltd.) and 0.6 parts by mass of sodium sulfate were added to the monomer solution to prepare a mixed solution. The water content of this liquid mixture was 2.5 mass%.
Next, 5.8 parts by mass of molecular sieves 5A as a dehydrating agent are added to the mixed solution with respect to 100 parts by mass of the polymerizable monomer component, and the mixture is stirred to prepare a mixture. The used dehydrating agent and inorganic salt were removed to prepare a polymerizable solution. This polymerizable solution had a water content of 0.5% by mass.
The water content was measured by the Karl Fischer titration method (direct titration method). Specifically, a Karl Fischer moisture measuring device MKC-510N (manufactured by Kyoto Electronics Industry Co., Ltd.) was used as a measuring device. More specifically, 70 to 100 mg of sample was collected with a syringe, and injected into the electrolysis cell of the apparatus for measurement. In addition, about the sample amount, the mass at the time of extract | collecting a sample with a syringe and the mass of the syringe after injection | pouring were measured, the difference was computed, and this difference was made into the sample amount. Further, Aquamicron AKX and Aquamicron CXU (manufactured by API Corporation) were used as the anolyte and catholyte at the time of sample measurement, respectively. This measurement was performed at room temperature (about 20 ° C.). The number of test of the sample was 3, and the arithmetic average value was defined as the amount of water (% by mass) contained in the sample.

(Example 1: Polymerization and foaming)
1500 g of the polymerizable solution was placed in a Teflon cuboid mold having an internal method of 25 mm × 210 mm × 360 mm.
When the polymerizable solution was heated at 50 ° C. in a nitrogen atmosphere for each mold, the surface of the polymerizable solution was cured in about 10 hours after the start of heating, and a foamable polymer (density: 1.15 g / cm ³ ). was gotten.
Then, the foamable polymer is put into a hot air circulating furnace and heated to a temperature at which urea (thermal decomposition temperature: 135 ° C.) decomposes or more (specifically, heated at a furnace temperature of 170 ° C. for 1 hour) The foaming agent (urea) was decomposed and foamed to produce an acrylic resin foam (apparent density: 0.046 g / cm ³ ). The acrylic resin foam was white. Further, the bubbles were relatively uniform, and no voids were confirmed.
The presence or absence of voids was confirmed as follows. That is, a sample having a thickness of 25 mm × vertical 200 mm × horizontal 200 mm is cut out from the obtained acrylic resin foam, excluding the foam skin. This sample was divided into three by a slicer in the thickness direction, and bubbles in a slice cross section of 200 mm × 200 mm were observed, and bubbles having a major axis of 2 mm or more were made voids. Voids were observed on two different sections divided into three, and the numbers were totaled. If there were 1 or more voids, there was a void, and if there were 0 voids, there was no void.

(Example 2)
A polymerizable solution was prepared in the same manner as in Example 1 except that 23.2 parts by mass of Molecular Sieves 5A as a dehydrating agent was added to 100 parts by mass of the polymerizable monomer component. This polymerizable solution had a water content of 0.3% by mass.
A foamable polymer (density: 1.15 g / cm ³ ) was obtained in the same manner as in Example 1 except that the polymerizable solution of Example 2 was used. The surface of the polymerizable solution was cured about 9 hours after the start of heating.
Thereafter, an acrylic resin foam (apparent density: 0.046 g / cm ³ ) was produced in the same manner as in Example 1 except that the foamable polymer of Example 2 was used. The acrylic resin foam was white. Further, the bubbles were relatively uniform, and no voids were confirmed.

(Comparative Example 1)
A polymerizable solution was prepared in the same manner as in Example 1 except that Molecular Sieves 5A as a dehydrating agent was not used. This polymerizable solution had a water content of 3.6% by mass.
A foamable polymer (density: 1.15 g / cm ³ ) was obtained in the same manner as in Example 1 except that the polymerizable solution of Comparative Example 1 was used. The surface of the polymerizable solution was cured about 13 hours after the start of heating.
Thereafter, an acrylic resin foam (apparent density: 0.046 g / cm ³ ) was produced in the same manner as in Example 1 except that the foamable polymer of Comparative Example 1 was used. The acrylic resin foam was white. In addition, voids were confirmed.

As described above, in the methods of Examples 1 and 2 within the scope of the present invention, the polymerizable solution is heated and cured as compared with Comparative Example 1 using a polymerizable solution having a moisture content of 3.6% by mass. The time to do was short.
Therefore, according to the present invention, it can be understood that the polymerization reaction of the polymerizable monomer component can be promoted, and as a result, the acrylic resin foam can be produced in a shorter time than conventional.
In addition, the acrylic resin foam produced by the methods of Examples 1 and 2 within the scope of the present invention was an acrylic produced by the method of Comparative Example 1 using a polymerizable solution having a moisture content of 3.6% by mass. Unlike the resin foam, no voids were observed.
From this, it can be seen that according to the present invention, voids are hardly generated.

Claims (2)

Foaming obtained by polymerizing the polymerizable monomer component by heating a polymerizable solution containing a polymerizable monomer component containing an acrylic monomer, a foaming agent containing urea, and a polymerization initiator, and then polymerizing the polymerizable monomer component A method for producing an acrylic resin foam in which an acrylic resin foam is formed by foaming by heating a functional polymer,
A method for producing an acrylic resin foam, wherein the polymerization is carried out by heating the polymerizable solution having a moisture content of 0.3 to 2% by mass in an inert gas atmosphere. The method for producing an acrylic resin foam according to claim 1, wherein nitrogen gas is used as the inert gas.