JP2014189699A - Method for manufacturing acrylic polymerized molded body, and method for manufacturing foam molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an acrylic polymerized molded body capable of manufacturing a foam molded body with reduced occurrence of voids and a method for manufacturing a foam molded body.SOLUTION: A method for manufacturing an acrylic polymerized molded body includes: the step (I) of heating and polymerizing a polymerizable solution containing an acrylic monomer, a chemical foaming agent, and a polymerization initiator so as to obtain a precursor molded body containing an unreacted monomer whose volume shrinkage with respect to a total volume of the polymerizable solution before polymerization is 14% or more; and the step (II) of heating the precursor molded body at a polymerization temperature higher than a polymerization temperature in the step (I) so as to polymerize the unreacted monomer and obtain an acrylic polymerized molded body. A rate of temperature increase when increasing the temperature of the precursor molded body until reaching the polymerization temperature in the step (II) is 4.0°C/hour or less. A method for manufacturing a foam molded body includes subjecting the acrylic polymerized molded body obtained in the foregoing manufacturing method to heat foaming.

Description

  The present invention relates to a method for producing an acrylic polymer molded article and a method for producing a foam molded article.

  A foam molded product obtained by heating and foaming an acrylic polymer molded product is excellent in strength and light transmittance, light weight, and heat insulation, so it is used for a lighting heat insulating material and a medical X-ray base material. In addition, fiber reinforced plastics (FRP) is affixed to the surface and used as a member for constituting a wall material of a cold storage room of a cargo vehicle and a hull of a small boat.

As a manufacturing method of the said foaming molding, the method shown below is mentioned, for example.
A polymerizable solution in which an acrylic monomer, urea as a chemical foaming agent, and a polymerization initiator are mixed is prepared, the polymerizable solution is poured into a mold, and the mold is heated and polymerized to form an acrylic. A polymerized molded article is obtained. Thereafter, the obtained acrylic polymer molded body is heated to a temperature at which urea is decomposed to generate gas and foam, thereby obtaining a foam molded body (for example, Patent Document 1).

  In the method of Patent Document 1, in the polymerization of the polymerizable solution, after heating until the volume reaches a predetermined ratio due to curing shrinkage accompanying the progress of polymerization, unreacted remaining by heating at a higher temperature It is performed to complete the polymerization reaction by reacting these monomers. Specifically, for example, the entire mold is heated at 50 ° C. for 10 hours to solidify by performing a polymerization reaction, and then heated at 80 ° C. for 3 hours to complete the polymerization reaction. Getting is done.

  However, in such a conventional manufacturing method, bubbles that are significantly larger than the surrounding bubbles may be generated in the obtained foamed molded article. If voids occur in the foamed molded product, there will be a difference in light transmission between the voids and other parts. For applications that require particularly uniform light transmission, such as medical X-ray core materials. Not applicable. For this reason, it is important to stably suppress the generation of voids in the foamed molded product.

Japanese Examined Patent Publication No. 50-038143

  The present invention provides a method for producing an acrylic polymer molded article and a method for producing a foam molded article, which can produce a foam molded article in which generation of voids is suppressed.

  In the method for producing an acrylic polymer molded body of the present invention, a polymerizable solution containing an acrylic monomer, a chemical foaming agent and a polymerization initiator is heated and polymerized, and the volume relative to the total volume of the polymerizable solution before polymerization. Step (I) of obtaining a precursor molded body containing an unreacted monomer having a shrinkage ratio of 14% or more, and heating the precursor molded body at a polymerization temperature higher than the polymerization temperature of the step (I) A step (II) of polymerizing the unreacted monomer to obtain an acrylic polymer molded body, and raising the temperature of the precursor molded body until reaching the polymerization temperature of the step (II) The rate of temperature rise is 4.0 ° C./hour or less.

  The method for producing a foamed molded product of the present invention is a method in which an acrylic polymer molded product obtained by the method for producing an acrylic polymer molded product of the present invention is heated and foamed.

If the acrylic polymer molded body obtained by the method for producing an acrylic polymer molded body of the present invention is used, a foam molded body in which generation of voids is suppressed can be obtained.
According to the method for producing a foamed molded product of the present invention, a foamed molded product in which generation of voids is suppressed is obtained.

  In the present specification, “(meth) acrylic acid” means one or both of methacrylic acid and acrylic acid, and the same applies to other compounds.

<Method for producing acrylic polymer molded article>
The method for producing an acrylic polymer molded article of the present invention is a method having the following steps (I) and (II).
(I) A polymerizable solution containing an acrylic monomer, a chemical foaming agent and a polymerization initiator is heated and polymerized, and the volume shrinkage ratio with respect to the total volume of the polymerizable solution before polymerization is 14% or more. A precursor molded body containing the monomer for the reaction is obtained.
(II) The precursor molded body is heated at a polymerization temperature higher than the polymerization temperature in step (I), and the unreacted monomer is polymerized to obtain an acrylic polymer molded body.

[Step (I)]
A polymerizable solution containing an acrylic monomer, a chemical foaming agent, and a polymerization initiator shrinks in volume due to curing shrinkage as the polymerization reaction proceeds by heating. In step (I), the polymerization is allowed to proceed until the volume shrinkage with respect to the total volume of the polymerizable solution before polymerization reaches 14% or more, thereby obtaining a solidified precursor molded body in which unreacted monomers remain inside. . If the volume shrinkage is less than 14%, the amount of unreacted monomer remaining in the precursor molded body becomes too large, and bubbles are generated during polymerization of the unreacted monomer in step (II). This cannot be sufficiently suppressed.
The heating in the step (I) may be performed until the volume shrinkage rate reaches 14%, or may be performed until the volume shrinkage rate exceeds 14%. The heating in the step (I) is preferably performed until the volume shrinkage rate is 14 to 20%. If the heating in the step (I) is performed until the volume shrinkage rate is equal to or lower than the upper limit value, sufficient productivity is easily obtained.

  In step (I), for example, a precursor solution having a desired shape can be obtained by placing the polymerizable solution in a mold having a predetermined shape and heating. A formwork can be suitably determined according to the shape of the target acrylic polymer molding.

  40-57 degreeC is preferable and, as for the polymerization temperature in process (I), 46-56 degreeC is more preferable. If the polymerization temperature in the step (I) is at least the lower limit, the polymerization reaction is likely to proceed sufficiently, and productivity is easily obtained. If the polymerization temperature in the step (I) is not more than the upper limit value, the polymerization reaction becomes more stable and voids are hardly generated.

  The polymerization time in step (I) is preferably 10 to 45 hours, and more preferably 15 to 35 hours. If the polymerization time in the step (I) is at least the lower limit value, the polymerization reaction is likely to proceed sufficiently and voids are less likely to occur. If the polymerization time in step (I) is less than or equal to the upper limit value, the productivity will be high.

  The polymerizable solution is a solution containing an acrylic monomer, a chemical foaming agent and a polymerization initiator as essential components, and if necessary, other monomers other than the acrylic monomer, a polymerization initiation assistant, Substance ion addition substances, dehydrating agents, polymerization inhibitors, bubble regulators, and the like may be mixed.

(Acrylic monomer)
Examples of the acrylic monomer include (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, crotonic acid, methyl (meth) acrylate, ethyl (meth) acrylate, (Meth) butyl acrylate, (meth) acrylate lauryl, (meth) acrylate 2-ethylhexyl, (meth) acrylate cyclohexyl, (meth) acrylate benzyl, (meth) acrylamide, maleate amide, maleate imide, etc. Is mentioned.

As the acrylic monomer, a water-soluble acrylic monomer is preferable, (meth) acrylic acid is more preferable, and methacrylic acid is preferable in view of excellent solubility in urea used as a chemical foaming agent. Particularly preferred.
In addition, as the acrylic monomer, methyl methacrylate is preferable in that the foamability of the acrylic polymer molded body becomes better.
Only one type of acrylic monomer may be used, or two or more types may be used.

(Other monomers)
The other monomer may be any monomer that can be copolymerized with an acrylic monomer, and can be appropriately selected and used for the purpose of modifying a foamed molded product.
As the other monomer, styrene is preferable from the viewpoint that the foamability of the acrylic polymer molded article becomes better. When styrene is used, the amount of styrene used is preferably 20% by mass or less with respect to the total amount of monomers because the hardness of the foamed molded article is not easily impaired.
One other monomer may be used, or two or more other monomers may be used.

As a monomer used for polymerization, a monomer mixture containing (meth) acrylic acid, methyl methacrylate and styrene is preferable, and a monomer mixture consisting of (meth) acrylic acid, methyl methacrylate and styrene is more preferable. A monomer mixture consisting of 50 to 70% by weight of methyl methacrylate, 20 to 30% by weight of (meth) acrylic acid, and 10 to 20% by weight of styrene is particularly preferred.
When the ratio of (meth) acrylic acid is in the range of 20 to 30% by mass, only the acrylic acid may be used as the above range, or only methacrylic acid may be used as the above range, and the total of acrylic acid and methacrylic acid may be used as the above range. Also good.

(Chemical foaming agent)
The chemical foaming agent is not particularly limited as long as the foamed molded product can be obtained by heating and foaming the acrylic polymer molded product, and is preferably at least one selected from the group consisting of urea and urea derivatives.
Only one type of chemical foaming agent may be used, or two or more types may be used.

  1.0-15 mass parts is preferable with respect to 100 mass parts of the whole quantity of the monomer used for superposition | polymerization, and, as for the usage-amount of a chemical foaming agent, 2.0-10 mass parts is more preferable. If the usage-amount of the said chemical foaming agent is more than a lower limit, the foaming molding excellent in the lightness will be easy to be obtained. If the usage-amount of the said chemical foaming agent is below an upper limit, it will become easy to dissolve a chemical foaming agent in a monomer. Moreover, if the usage-amount of the said chemical foaming agent is below an upper limit, it will become difficult to remain a chemical foaming agent in a foaming molding, and it will become difficult to produce foam breakage at the time of heat foaming.

As the polymerization initiator, a redox polymerization initiator is preferable.
Examples of the redox polymerization initiator include t-butyl hydroperoxide, cumene hydroxy peroxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, and the like. Is mentioned.

One or more polymerization initiators may be used.
As for the usage-amount of a polymerization initiator, 0.1-5.0 mass parts is preferable with respect to 100 mass parts of whole quantity of a monomer.

Examples of the polymerization initiation aid include sulfinic acid metal salts and amine compounds.
Examples of the sulfinic acid metal salt include sodium benzenesulfinate, sodium toluenesulfinate, sodium hydroxymethanesulfinate and the like. Among these, as the metal sulfinate, sodium hydroxymethanesulfinate is preferable.
Examples of the amine compound include N, N-dimethylaniline and triethylamine.

One type of polymerization initiation assistant may be used, or two or more types may be used.
As for the usage-amount of a polymerization start adjuvant, 0.1-25 mass parts is preferable with respect to 100 mass parts of whole quantity of a monomer. Moreover, the amount of the polymerization initiation aid used is preferably 0.1 to 5.0 times in terms of mass ratio with respect to the redox polymerization initiator.

Any substance capable of adding chloride ions to the polymerizable solution may be used as the substance for adding chloride ions. Chloride ions contribute to the acceleration of the polymerization reaction.
Examples of substances for adding chloride ions include sodium chloride, copper chloride, ferric chloride, silver chloride, gold chloride, hydrochloric acid, imidazolium salt surfactants, quaternary ammonium salt surfactants, alkylbetaines. Type amphoteric surfactants and the like.

  Examples of the imidazolium salt type surfactant include 1,3-dimethylimidazolium chloride, 1-butyl-3-methylimidazolium 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 the like.

Examples of the quaternary ammonium salt type surfactant include cetyltrimethylammonium chloride, lauryltrimethylammonium chloride, dodecyltrimethylammonium chloride, stearyltrimethylammonium chloride, coconut alkyltrimethylammonium chloride, beef tallow alkyltrimethylammonium chloride, behenyltrimethylammonium chloride. , Polydiallyldimethylammonium chloride, dialkyldimethylammonium chloride and the like.
Examples of the alkylbetaine-type amphoteric surfactant include lauryldimethylaminoacetic acid betaine and myristylbetaine.

  The substance for adding chloride ions is preferably at least one selected from the group consisting of sodium chloride, hydrochloric acid, cetyltrimethylammonium chloride, and lauryltrimethylammonium chloride, and more preferably cetyltrimethylammonium chloride and lauryltrimethylammonium chloride.

The substance for adding chloride ions may be one kind or two or more kinds.
As for the usage-amount of the substance for chloride ion addition, 0.005-5.0 mass part is preferable with respect to 100 mass parts of whole quantity of a monomer.

Examples of the dehydrating agent include sulfates such as anhydrous sodium sulfate and anhydrous magnesium sulfate, and zeolite (molecular sieve).
Examples of the polymerization inhibitor include alkaline earth metal salts such as calcium formate.
Examples of the air conditioner include powdered inorganic substances such as metal oxides and diatomaceous earth.

The polymerizable solution is preferably filtered using a filter member having a mesh having a mesh size of less than 0.15 mm before pouring into the mold. Thereby, the foreign material in a polymeric solution is removed and generation | occurrence | production of the void resulting from this foreign material can be suppressed.
Examples of the filtering member having a mesh with a mesh size of less than 0.15 mm include a 200 mesh strainer (mesh size 0.077 mm).

[Step (II)]
In step (II), the precursor molded body is heated at a polymerization temperature higher than the polymerization temperature in step (I), and the unreacted monomer remaining inside the precursor molded body is polymerized to complete the polymerization reaction. To obtain an acrylic polymer molded body.
In the present invention, when the temperature of the precursor molded body is increased until the polymerization temperature in step (II) is reached, the temperature increase rate is 4.0 ° C./hour or less. As a result, the unreacted monomer in the precursor molded body is rapidly heated and vaporized, and bubbles are suppressed, so that voids are formed in the resulting acrylic polymer molded body. Can be suppressed. Therefore, if this acrylic polymer molded body is used, a high-quality foam molded body in which the generation of voids is suppressed can be obtained.

When the temperature of the precursor molded body is increased until the polymerization temperature in step (II) is reached, the temperature may be increased at a time until the polymerization temperature is reached, and the temperature increase is performed in multiple steps. Also good.
When the temperature rise is divided into a plurality of steps and performed in stages, the temperature difference between the temperature of the precursor molded body at the start of the temperature rise and the polymerization temperature in the step (II) is determined from the point at which the temperature rise is started ( The value divided by the time required to reach the polymerization temperature in II) is regarded as the rate of temperature increase.

  The rate of temperature increase is 4.0 ° C./hour or less, and 3.5 ° C./hour or less is preferable from the viewpoint of easily suppressing the generation of voids. In addition, the temperature increase rate is preferably 1.0 ° C./hour or more, more preferably 1.5 ° C./hour or more, from the viewpoint of higher productivity.

  57-80 degreeC is preferable and, as for the polymerization temperature in process (II), 58-65 degreeC is more preferable. If the said polymerization temperature is more than a lower limit, it will be easy to fully react an unreacted monomer. If the said polymerization temperature is below an upper limit, it will be easy to suppress the thermal deterioration of an acrylic polymer molding.

The polymerization time in step (II) is preferably 3.0 to 20 hours, more preferably 5.0 to 12 hours. If the said polymerization time is more than a lower limit, it will be easy to fully react an unreacted monomer. Productivity will become high if the said polymerization time is below an upper limit.
The polymerization time in the step (II) is a time during which the precursor molded body is heated at a temperature higher than the polymerization temperature in the step (I), and includes the time required for temperature increase.

Step (I) and step (II) may be performed continuously or intermittently.
Specifically, for example, after the polymerization reaction in step (I), in the same heating arrangement, the precursor molded body is heated by heating from the polymerization temperature in step (I) until the polymerization temperature in step (II) is reached. After the polymerization reaction in the step (I), the precursor molded body is moved to another heating facility, and the precursor molded body having a temperature lower than the polymerization temperature in the step (I) is changed to the step (II). Heating may be carried out by raising the temperature to the polymerization temperature in.

  The shape of the acrylic polymer molded body produced by the production method of the present invention is not particularly limited, and may be appropriately determined according to the shape of the target foam molded article. For example, when producing a plate-like foamed molded article, it is preferable to produce a plate-like acrylic polymer molded article.

  In the method for producing an acrylic polymer molded body of the present invention described above, the precursor molded body is heated at a temperature higher than that in step (I) to react with unreacted monomers remaining inside the precursor molded body. Thus, when the polymerization is completed, by setting the rate of temperature rise to a specific value or less, it is possible to prevent the unreacted monomer inside the precursor molded body from being rapidly heated and generating large bubbles. By using such an acrylic polymer molded body in which the formation of large bubbles is suppressed, it is possible to suppress the generation of voids in the foam molded body.

<Method for producing foam molded article>
The method for producing a foamed molded product of the present invention is a method for obtaining a foamed molded product by heating and foaming the acrylic polymer molded product obtained by the above-described method for producing an acrylic polymer molded product of the present invention. As the method for producing the foamed molded article of the present invention, a known method can be adopted except that the acrylic polymer molded article obtained by the above-described method for producing an acrylic polymer molded article of the present invention is used.
For example, when producing a plate-like foamed molded article, a plate-like acrylic polymer molded article is placed between a pair of heat plates of a mold having two heat plates separated by an arbitrary distance, and these heat plates are used. The acrylic polymer molded body is heated. When the acrylic polymer molded body is heated to a temperature higher than the thermal decomposition temperature of the chemical foaming agent, the acrylic polymer molded body foams and expands on the heat plate, and a foam molded body having a predetermined expansion ratio is obtained. .

  The mold used for heating and foaming is not limited to the above-described one, and may be appropriately selected according to the shape of the target foamed molded product. A foamed molded article having a desired shape can be obtained by heating and foaming the acrylic polymer molded article in a mold having a desired inner method.

The heating temperature for heating and foaming the acrylic polymer molded body is not less than the temperature at which the acrylic polymer molded body is softened and not less than the thermal decomposition temperature of the chemical foaming agent contained in the acrylic polymer molded body.
For example, when the chemical foaming agent is urea (thermal decomposition temperature 135 ° C.), the heating temperature is preferably 135 ° C. or higher, and more preferably 145 ° C. or higher. Foaming progresses more efficiently as the heating temperature is higher. The heating temperature is preferably 200 ° C. or lower, and more preferably 180 ° C. or lower. If heating temperature is below an upper limit, the shrinkage | contraction accompanying the thermal deterioration of a foaming molding can be prevented.

It is preferable that the dimensional change rate of the foamed molded product after foaming with respect to the acrylic polymer molded product before foaming is as uniform as possible in all directions. Thereby, it becomes easy to obtain the foaming molding by which generation | occurrence | production of the crack was suppressed.
Specifically, when a rectangular plate-like foamed molded article is manufactured, the dimensional change rate (L) in the longitudinal direction obtained by the following formula (1) and the dimension in the short direction obtained by the following formula (2). The ratio (L / D) to the rate of change (D) is preferably 1 / 1.3-1.3 / 1, more preferably 1 / 1.2-1.2 / 1. When the ratio (L / D) is within the above range, it is easy to obtain a foamed molded article in which the occurrence of cracks is sufficiently suppressed.
L = L2 / L1 (1)
D = D2 / D1 (2)
However, in said formula, L1 is the length of the longitudinal direction of the acrylic polymer molding before foaming, L2 is the length of the longitudinal direction of the resin molding after foaming. D1 is the length in the short direction of the acrylic polymer molded body before foaming, and D2 is the length in the short direction of the resin molded body after foaming.
The dimensional change rates (L) and (D) can be adjusted, for example, by adjusting the inner method of the mold.

Apparent density of the foamed article produced by the production method of the present invention is preferably 0.035~0.200g / cm ^3, more preferably 0.040~0.150g / cm ^3, 0.045~0. 125 g / cm ³ is more preferable. If the apparent density of the foamed molded product is equal to or higher than the lower limit, the expansion ratio does not become too high, and cracks are hardly generated in the foamed molded product. If the apparent density of the foamed molded product is not more than the upper limit value, the lightweight property of the foamed molded product becomes better.
In addition, the apparent density of a foaming molding is measured by the method as described in an Example.

  According to the method for producing a foamed molded product of the present invention described above, since the acrylic polymer molded product obtained by the method of the present invention is used, a high-quality foam molded product in which generation of voids is suppressed is obtained. Can be obtained.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[Apparent density of foam molding]
The apparent density of the foamed molded product obtained in each example was measured by a method based on the method described in JIS K 7222: 1999. Specifically, from the obtained foamed molded article, a test piece having a volume of 10 cm ³ or more was cut out so as not to change the cell structure, the mass of the test piece was measured, and the apparent density was calculated by the following equation.
Apparent density (g / cm ³ ) = Mass of test piece (g) / Volume of test piece (cm ³ )

[Measure the number of voids]
From the portion excluding the foam skin in the obtained foamed molded article, a test piece having a thickness of 10 mm × length of 900 mm × width of 900 mm was cut out, and both cut surfaces (900 mm × 900 mm) of the test piece were visually observed, Bubbles having a diameter of 2 mm or more were measured as voids.
The measurement was performed on 10 test pieces obtained from the same foamed molded article, and the arithmetic average value was defined as the number of voids generated.

[Example 1]
(Manufacture of acrylic polymer moldings)
Step (I):
5 parts by mass of urea as a chemical foaming agent is mixed with 100 parts by mass of a monomer mixture consisting of 61% by mass of methyl methacrylate, 24% by mass of methacrylic acid, and 15% by mass of styrene, and dissolved uniformly. A meter solution was prepared. Thereafter, with respect to 100 parts by mass of the monomer mixture, 0.5 parts by mass of t-butyl hydroperoxide (“Perbutyl H-69” manufactured by NOF Corporation) as a polymerization initiator and N, N as polymerization initiation assistants. -0.5 part by mass of dimethylaniline, 0.04 part by mass of cetyltrimethylammonium chloride (“Nissan Cation PB-40R” manufactured by NOF Corporation) as a substance for adding chloride ions, 0.6 part by mass of sodium sulfate, and calcium formate A polymerizable solution was prepared by adding 0.14 parts by mass to the monomer solution.
Next, after passing 8300 g of the polymerizable solution through a strainer mesh (60 mesh strainer) having a mesh size of 0.300 mm, the polymerized solution is put into a polyethylene rectangular form having an internal method of 1000 mm × 370 mm × 25 mm. It was. Thereafter, the polymerizable solution was heated together with the mold in a nitrogen atmosphere at 56 ° C. for 5 hours and at 49 ° C. for 20 hours to obtain a solid plate-like precursor molded body containing an unreacted monomer. At this time, the volume shrinkage of the precursor molded body with respect to the total volume of the polymerizable solution before polymerization was 14%.

Process (II):
Thereafter, the temperature is raised to 59.0 ° C. over 2.5 hours at a temperature increase rate of 4.0 ° C./hour, and the precursor compact is heated at 59.0 ° C. for 6.5 hours. The polymer was polymerized to obtain a plate-like acrylic polymer molded body.

(Manufacture of foam moldings)
The obtained plate-like acrylic polymer molded body was cut to 8140 g, put into a mold having an internal method of 1820 mm × 910 mm × 75 mm, and heated to 170 ° C. which is higher than the thermal decomposition temperature (135 ° C.) of urea. It heated and foamed and obtained the plate-shaped foaming molding.
The obtained foamed molded product was white and the apparent density was 0.063 g / cm ³ .

[Example 2]
In Example (II), except that the temperature was increased to 59.0 ° C. over 4.5 hours at a temperature increase rate of 2.2 ° C./hour, and the precursor compact was heated at 59.0 ° C. for 4.5 hours. In the same manner as in Example 1, an acrylic polymer molded product was produced to obtain a foam molded product.

[Example 3]
An acrylic polymer molded product was produced in the same manner as in Example 1 except that the strainer mesh used was changed to one having a mesh size of 0.077 mm (200 mesh strainer) to obtain a foam molded product.

[Example 4]
The strainer mesh to be used is changed to one having a mesh size of 0.077 mm (200 mesh strainer), and in step (II), the temperature rise rate is 2.2 ° C./hour up to 59.0 ° C. over 4.5 hours. An acrylic polymer molded body was produced in the same manner as in Example 1 except that the temperature was raised and the precursor molded body was heated at 59.0 ° C. for 4.5 hours, to obtain a foam molded body.

[Comparative Example 1]
A precursor molded body was obtained in the same manner as in Example 1 except that the polymerization conditions in the step (I) were changed to 50 ° C. and 10 hours. At this time, the volume shrinkage of the precursor molded body with respect to the total volume of the polymerizable solution before polymerization was 7%. Thereafter, in step (II), the temperature was increased to 80.0 ° C. over 1.0 hour at a temperature increase rate of 30.0 ° C./hour, and the precursor molded body was heated at 80.0 ° C. for 2.0 hours. In the same manner as in Example 1, an acrylic polymer molded article was produced, and a foam molded article was obtained.

[Comparative Example 2]
Example except that the temperature was raised to 59.0 ° C. over 2.0 hours at a temperature rising rate of 5.0 ° C./hour in Step (II), and the precursor compact was heated at 59.0 ° C. for 7.0 hours. In the same manner as in Example 1, an acrylic polymer molded product was produced to obtain a foam molded product.

[Comparative Example 3]
The strainer mesh to be used is changed to one having a mesh size of 0.077 mm (200 mesh strainer). In step (II), the temperature rise rate is 5.0 ° C./hour up to 59.0 ° C. over 2.0 hours. An acrylic polymer molded body was produced in the same manner as in Example 1 except that the temperature was raised and the precursor molded body was heated at 59.0 ° C. for 7.0 hours to obtain a foam molded body.

[Comparative Example 4]
A precursor molded body was obtained in the same manner as in Example 1 except that the polymerization conditions in the step (I) were changed to conditions of heating at 56 ° C. for 5 hours and then heating at 49 ° C. for 10 hours. At this time, the volume shrinkage ratio of the precursor molded body with respect to the total volume of the polymerizable solution before polymerization was 11%. Thereafter, an acrylic polymer molded product was produced in the same manner as in Example 1 except that the strainer mesh used was changed to a mesh having a mesh size of 0.077 mm (200 mesh strainer), to obtain a foam molded product. .

The conditions of steps (I) and (II) in each example, the volume shrinkage ratio with respect to the total volume of the polymerizable solution of the precursor molded body obtained in step (I), and the number of voids generated in the obtained foam molded body are shown. It is shown in 1.
In addition, all of the apparent density of the foaming moldings obtained in Examples 2 to 4 and Comparative Examples 1 to 4 were 0.063 g / cm ³ .

As shown in Table 1, after heating in step (I) until the volume shrinkage becomes 14%, in step (II), the precursor compact is heated at a rate of temperature increase of 4.0 ° C./hour or less and heated. In Examples 1 to 4 in which the above was performed, generation of voids was suppressed.
On the other hand, many voids were generated in Comparative Example 1 in which the volume shrinkage of the precursor molded body was less than 14% in the step (I) and the temperature increase rate in the step (II) exceeded 4.0 ° C./hour.
Further, in the comparative examples 2 and 3 in which the temperature increase rate in the step (II) exceeds 4.0 ° C./hour, although the volume shrinkage ratio of the precursor molded body is heated to 14% in the step (I), Generation was not sufficiently suppressed.
Further, in Comparative Example 4 in which the volume shrinkage ratio of the precursor molded body in the step (I) is less than 14%, the rate of temperature increase in the step (II) is 4.0 ° C./hour or less, but generation of voids is sufficient. Was not suppressed.

Claims (2)

A polymerizable solution containing an acrylic monomer, a chemical foaming agent and a polymerization initiator is polymerized by heating, and a volume shrinkage ratio of 14% or more with respect to the total volume of the polymerizable solution before polymerization is 14% or more. Step (I) for obtaining a precursor molded body containing a monomer,
Heating the precursor molded body at a polymerization temperature higher than the polymerization temperature of the step (I), polymerizing the unreacted monomer to obtain an acrylic polymer molded body, and (II),
A method for producing an acrylic polymer molded article, wherein a rate of temperature rise when the temperature of the precursor molded article is raised until reaching the polymerization temperature in the step (II) is 4.0 ° C / hour or less.   The manufacturing method of a foaming molding which heat-foams the acrylic polymer molding obtained by the manufacturing method of Claim 1.