JP2006241256A - Expandable methyl methacrylate resin particle and foam obtained using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methyl methacrylate resin foam which shows a good moldability in a high expansion ratio, hardly emits soot and smoke at ignition and is suitably used for a sublimation pattern used for metal casting or a building structure. <P>SOLUTION: A molded product obtained through expansion molding of an expandable methyl methacrylate resin particle has a mean bubble chord length of 70-200 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an expandable methyl methacrylate resin particle and a methyl methacrylate resin foam using the same. More specifically, the present invention relates to expandable methyl methacrylate resin particles having good moldability at a high expansion ratio and a methyl methacrylate resin foam having a good appearance using the same. Further, the present invention relates to a methyl methacrylate-based resin foam suitable for use in a disappearance model or a building structure used in metal casting, which hardly generates soot when ignited.

  Foaming of methyl methacrylate polymers is generally difficult, the elongational viscosity and shear viscosity at the time of melting are not suitable for the foaming behavior, and the ability to retain bubbles is insufficient. For this reason, not only does it not sufficiently foam, the foam cells become uneven, the surface of the obtained foam has many irregularities, and it is difficult to form a smooth surface, and even if it is slightly foamed, the shrinkage of bubbles is intense and has commercial value It was difficult to obtain a foam. As means for improving foaming performance, Patent Document 1 discloses that a thermoplastic polymer particle is suspended in water containing a dispersant for particle size control, and a methacrylic acid ester-based polymer is added to the suspension. A method is disclosed in which the monomer is dropped and polymerized in a specific ratio with respect to the thermoplastic polymer to reduce nonuniformity in the molecular weight distribution of the resulting polymer particles. Moreover, as a method for improving the retention of the foaming agent, Patent Document 2 discloses a method of adjusting the molecular weight in a specific region. In addition, as a method of obtaining a foam having a high foaming ratio, uniform foam cells and good appearance at the time of foam molding, the polymer obtained from a specific monomer ratio in Patent Document 3 is adjusted to a specific molecular weight. A method is disclosed.

  By the way, when using a methyl methacrylate-based resin foam for disappearance models and building structures used in metal casting, the weight of the resin used is smaller, that is, the higher the foaming ratio of the foamed molded product, the more industrial Value increases. In these applications, the dimensional stability of the foamed molded product obtained is also cited as one of the important required qualities.

However, the resins described in Patent Documents 1, 2, and 3 have a problem that a large dimensional change is observed in a foamed molded product obtained in a high expansion ratio state. The reason for this is that not only the foamed cells are not sufficiently uniform, but also the cell size becomes too small, the film thickness of the cells constituting the bubbles becomes thin, and the foaming performance is not always sufficient. On the other hand, foamed cells of expandable styrenic resin are prone to non-uniformity and coarsening, so a method of using a nucleating agent having the ability to make the foamed cells uniform and fine has been proposed. Yes. However, even if it has the same problem, it cannot be solved by diverting the technology in the expandable styrene resin to the expandable methyl methacrylate resin particles. First, as described in Patent Document 3, the present applicant has succeeded in homogenizing the foamed cells with respect to the foamable methyl methacrylate resin particles. The average chord length is about 50 μm at most, and it has been desired to reduce the dimensional change in the foamed molded product obtained in a high foaming magnification state.
JP 50-127990 A JP 2001-123001 A JP 2001-233986 A

  In view of the situation as described above, the present invention has good moldability at a high expansion ratio, and further, smoke is hardly generated when ignited, and the disappearance model and building structure used in metal casting An object of the present invention is to provide a methyl methacrylate resin foam suitable for use in products.

  As a result of diligent investigations to solve the above problems, when the foam is adjusted to a specific foam cell size that is larger than the conventional foam cell size, the foam has good appearance and little shape change even at high foaming ratio during pre-foaming and foam molding. As a result, the present invention was found.

  Further, in the process of producing expandable methyl methacrylate resin particles, foaming is performed by adding a foaming agent while the amount of unreacted total residual monomer contained in the resin particles is within a specific range. The present inventors have found that the cell size can be adjusted efficiently and completed the present invention.

  That is, according to the first aspect of the present invention, the foamable methyl methacrylate series is characterized in that the average chord length of the cut cells of the molded body formed by foaming foamable methyl methacrylate resin particles is 70 μm or more and 200 μm or less. It relates to resin particles.

  As a preferred embodiment, from a methyl methacrylate monomer and a polyfunctional monomer of 0.02 vinyl group mol% to 0.20 vinyl group mol% with respect to the methyl methacrylate monomer The foamable methyl methacrylate resin particles described above are obtained by impregnating a methyl methacrylate resin particle having a weight average molecular weight of 250,000 to 500,000 with a foaming agent, which is obtained by polymerizing the monomer component. .

2nd of this invention is related with the foaming molding obtained by foam-molding the foamable methyl methacrylate resin particle of the said description.
A third aspect of the present invention is a foaming property characterized in that a methyl methacrylate-based monomer is polymerized and a foaming agent is added when the total residual monomer amount becomes 5% by weight or more and 20% by weight or less. Regarding the method for producing methyl methacrylate resin particles, a preferred embodiment is 0.02 vinyl group mol% or more and 0.20 vinyl group mol or less with respect to the methyl methacrylate monomer and the methyl methacrylate monomer. A foaming property characterized by polymerizing a monomer component composed of a polyfunctional monomer and adding a foaming agent when the total residual monomer amount becomes 5% by weight or more and 20% by weight or less. It is related with the manufacturing method of the said description of the methyl methacrylate resin particle.

  According to the present invention, when the average chord length of the cut cell of the molded body formed by foam molding of expandable methyl methacrylate resin particles is 70 μm or more and 200 μm or less, foaming at a high magnification is possible, and A molded article with good dimensional stability can be obtained. In other words, the dimensional stability that can be obtained only about 40 times as a foamed molded article in the prior art can be obtained even at a high foaming ratio of 60 times or more in the present invention.

  The foamable methyl methacrylate resin particles of the present invention are characterized in that when formed into a foam, the average chord length of the cut cells of the molded body is 70 μm or more and 200 μm or less. Preferably, they are 80 micrometers or more and 150 micrometers or less. By using expandable methyl methacrylate resin particles in which the average chord length of the cut bubbles in the molded product falls within the above range, it is possible to expand to a high magnification and obtain a molded product with good dimensional stability. It is possible.

  In the present invention, the average chord length of the cut bubbles in the molded product is determined by using a scanning electron micrograph of the foam cut surface according to ASTM-D-2842-97. It can be measured from the number.

  The resin that can be used for the expandable methyl methacrylate resin particles of the present invention may have any composition as long as the main component is a methyl methacrylate monomer. The monomer component is preferably composed of 0.02 vinyl group mol% or more and 0.20 vinyl group mol% or less polyfunctional monomer with respect to the methyl methacrylate monomer. By using the resin of the composition, foaming to high magnification is possible, and it is easy to obtain expandable methyl methacrylate-based resin particles that can be foamed with good appearance and little shape change during foam molding It is in. If the amount of the polyfunctional monomer is less than 0.02 vinyl group mol%, the moldability may be lowered, and if it is greater than 0.20 vinyl group mol%, the foaming rate may be lowered. Here, the vinyl group mol% is a unit expressing the equivalent of the functional group in%.

  As methyl methacrylate monomer, not only methyl methacrylate monomer, but also other single quantities within the range that does not impair the original characteristics of methyl methacrylate resin, which is excellent in weather resistance and hardly generates smoke when ignited It is possible to copolymerize with the body. Examples of copolymerizable monofunctional unsaturated monomers include, for example, methacrylates other than methyl methacrylate such as ethyl methacrylate, butyl methacrylate, and propyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate Acrylic acid esters such as 2-ethylhexyl acrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and itaconic acid; acid anhydrides such as maleic anhydride and itaconic anhydride; 2-hydroxyethyl acrylate Hydroxy group-containing esters such as 2-hydroxypropyl acrylate, monoglyceryl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, monoglyceryl methacrylate; acrylamide, methacrylamide, diacetone acrylamide That. Nitriles include nitrogen-containing monomers such as acrylonitrile, methacrylonitrile, diacetone acrylamide, and dimethylaminoethyl methacrylate; epoxy group-containing monomers such as acrylic glycidyl ether, glycidyl acrylate, and glycidyl methacrylate; styrene And styrene monomers such as α-methylstyrene.

  Among these, it is preferable to use acrylic acid ester and methacrylic acid ester.

  Examples of the polyfunctional monomer include ethylene glycol such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, etc. Esterified with an acid is one obtained by esterifying a hydroxyl group of a divalent alcohol such as neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, butanediol di (meth) acrylate with acrylic acid or methacrylic acid, Examples thereof include aryl compounds having two or more alkenyl groups such as divinylbenzene.

  The resin that can be used in the present invention preferably has a weight average molecular weight of 250,000 to 500,000. More preferably, it is 250,000 or more and 400,000 or less. When the weight average molecular weight is less than 250,000, the dimensional shrinkage when the foamed molded product is obtained may increase. If the weight average molecular weight is larger than 500,000, it may be difficult to increase the magnification because foamability is reduced, and not only the industrial value is lowered, but also the residue is likely to remain when used for disappearance models. May be difficult to obtain.

  The weight average molecular weight in the present invention is a value determined on the basis of a standard polystyrene (PS) sample by gel permeation chromatography (GPC).

  The foamable methyl methacrylate resin particles in the present invention are, for example, polymerized by suspension polymerization in the presence of a dispersant, a polymerization initiator, a chain transfer agent and various additives, and impregnated with the foaming agent. Can be obtained.

  Examples of the dispersant include dispersants generally used for suspension polymerization, for example, polymer dispersants such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylamide, such as poorly water-soluble such as calcium phosphate, hydroxyapatite, and magnesium pyrophosphate. Examples include inorganic salts. When a poorly water-soluble inorganic salt is used, an anionic surfactant such as α-olefin sodium sulfonate or dodecylbenzene sodium sulfonate is effective because the dispersion stability is increased. These dispersants may be added one or more times during the polymerization in order to adjust the particle diameter of the resulting foamable methyl methacrylate resin particles.

  Examples of the polymerization initiator that can be used in the suspension polymerization include polymerization initiators generally used for radical polymerization of methyl methacrylate monomers, such as benzoyl peroxide, lauroyl peroxide, t-butylperoxybenzoate, isopropyl- Organic peroxides and azo such as t-butyl peroxycarbonate, butyl perbenzoate, 1,1-bis (alkylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (alkylperoxy) cyclohexane Examples thereof include azo compounds such as bisisobutyronitrile, and these can be used in combination of two or more.

  The chain transfer agent may be a known one used for polymerization of methyl methacrylate. For example, monofunctional chain transfer agents such as alkyl mercaptans and thioglycolic acid esters, and polyhydric alcohol hydroxyl groups such as ethylene glycol, neopentyl glycol, trimethylolpropane and sorbitol are esterified with thioglycolic acid or 3-mercaptopropionic acid. And polyfunctional chain transfer agents.

  Examples of the blowing agent include aliphatic hydrocarbons that are hydrocarbons having 3 to 5 carbon atoms such as propane, isobutane, normal butane, isopentane, normal pentane, and neopentane, such as ozone such as difluoroethane and tetrafluoroethane. Examples thereof include volatile blowing agents such as hydrofluorocarbons having a destruction coefficient of zero. These foaming agents can be used in combination. The amount used is preferably 5 to 12 parts by weight, more preferably 7 to 10 parts by weight, based on 100 parts by weight of the methyl methacrylate resin particles.

  As said various additives, a plasticizer, a bubble regulator, etc. can be used according to the objective. Examples of the plasticizer include stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, stearic acid monoglyceride and other fatty acid glycerides, palm oil, palm oil, palm kernel oil and other vegetable oils, dioctyl adipate, dibutyl sebacate And the like, organic hydrocarbons such as liquid paraffin and cyclohexane, and organic aromatic hydrocarbons such as toluene and ethylbenzene. These may be used in combination. Examples of the air conditioner include aliphatic bisamides such as methylene bis stearic acid amide and ethylene bis stearic acid amide, polyethylene wax, and the like.

  Further, in producing the expandable methyl methacrylate resin particles of the present invention, the unreacted total residual monomer amount in the methyl methacrylate resin particles in the polymerization process is 5 wt% or more and 20 wt% or less. It is preferable to add a foaming agent at this point. More preferably, it is 8 to 15 weight%. By adding the foaming agent within the range, the viscosity of the resin particles is sufficiently lowered when the foaming agent is added, and the suspension stability is good, so that the foamed cells are uniform and the foamed cell size is enlarged. The dimensional stability of the molded product obtained is further improved and the resulting molded product becomes better.

  Furthermore, a monomer component comprising a methyl methacrylate monomer and a polyfunctional monomer of 0.02 vinyl group mol% to 0.20 vinyl group mol with respect to the methyl methacrylate monomer. When the total residual monomer amount becomes 5% by weight or more and 20% by weight or less, adding a foaming agent further improves the dimensional stability of the resulting molded product. Yes.

  In the present invention, the amount of unreacted total residual monomer can be measured by an internal standard method by gas chromatography.

  The expandable methacrylate ester resin particles of the present invention can be produced, for example, as follows.

  Water, a dispersant, and other additives are charged into a pressure vessel, a methyl methacrylate monomer, a polymerization initiator, and the like are charged, and polymerization is performed at 70 ° C. or higher and 90 ° C. or lower for about 3 to 6 hours. When the total amount of unreacted residual monomers contained in the resin particles is 5% by weight or more and 20% by weight or less, the foaming agent is 5 parts or more and 12 parts or less with respect to 100 parts by weight of the methacrylic ester resin particles. , Polymerized at 90 ° C. or higher and 120 ° C. or lower for 5 to 15 hours, cooled, washed, dehydrated, and dried to obtain expandable methacrylate ester resin particles.

  The foamable methyl methacrylate resin particles obtained in this way have good moldability at a high expansion ratio when formed into a molded body.

Examples and Comparative Examples are given below, but the present invention is not limited thereby.
<Measurement of bubble diameter>
The average cell diameter of the molded body was measured in accordance with ASTM-D-2842-97 from the bubble diameter on a straight line of the cut surface from a photograph of the cut surface of the foam projected.
<Dimensional shrinkage>
The dimensional shrinkage of the molded article was measured and evaluated as the difference between the mold dimension and the molded article dimension in the thickness direction after storing in a drying room at about 35 ° C. for one day after molding.
<Surface condition>
The surface state of the molded body was evaluated by visual observation after being molded for one day in a drying room at about 35 ° C.

Example 1
In a 6 L autoclave, 150 parts by weight of water, 0.15 part by weight of tribasic calcium phosphate, 0.008 part by weight of sodium α-olefin sulfonate, 0.08 part by weight of lauroyl peroxide, 1,1-bis (t-butylperoxy) 0.1 part by weight of cyclohexane, 0.1 part by weight of 1,6-hexanediol diacrylate (0.09 vinyl group mol% with respect to methyl methacrylate monomer), 0.26 part by weight of n-dodecyl mercaptan After charging, 94 parts by weight of methyl methacrylate, 6 parts by weight of methyl acrylate, and 1 part by weight of toluene were charged, and polymerization was carried out at 80 ° C. for about 4 hours. When 10% by weight of cyclohexane was added, 1 part by weight of cyclohexane and 9 parts of normal rich butane (normal / iso = 70/30) were charged at 100 ° C. Performed 10 hours the polymerization was then cooled to obtain a foamable methacrylate resin particles by washing, dehydration and drying.

The obtained expandable methyl methacrylate resin particles were classified by 0.6 to 1.0 mm and then pre-expanded to obtain pre-expanded particles with a 65-fold capacity. After the obtained pre-expanded particles were cured at room temperature for 1 day, a foam-molded product was obtained with a 300 × 450 × 150 (t) mm size mold using a Daisen KR-57 molding machine.
The results are shown in Table 1.

(Example 2)
In the same manner as in Example 1 except that cyclohexane and normal rich butane were charged when the total amount of unreacted residual monomers contained in the resin particles reached 8% by weight, the expandable methyl methacrylate resin particles were prepared as in Example 1. Obtained. The obtained expandable methyl methacrylate resin particles were evaluated by classification, preliminary foaming and molding in the same manner as in Example 1. The evaluation results are as shown in Table 1.

(Example 3)
In the same manner as in Example 1 except that cyclohexane and normal rich butane were charged when the total amount of unreacted residual monomers contained in the resin particles reached 16% by weight, the expandable methyl methacrylate resin particles were prepared as in Example 1. Obtained.

  The obtained expandable methyl methacrylate resin particles were evaluated by classification, preliminary foaming and molding in the same manner as in Example 1. The evaluation results were as shown in Table 1.

Example 4
The foamable methyl methacrylate type was the same as in Example 1 except that 0.15 parts by weight of 1,6-hexanediol diacrylate (0.13 vinyl group mol% with respect to the methyl methacrylate type monomer) was used. Resin particles were obtained.

  The obtained expandable methyl methacrylate resin particles were evaluated by classification, preliminary foaming and molding in the same manner as in Example 1. The evaluation results were as shown in Table 1.

(Comparative Example 1)
Expandable methyl methacrylate resin particles in the same manner as in Example 1 except that cyclohexane and normal rich butane were charged when the amount of unreacted total residual monomer contained in the resin particles became 1% by weight or less. Got.

  The obtained expandable methyl methacrylate resin particles were evaluated by classification, preliminary foaming and molding in the same manner as in Example 1. The evaluation results were as shown in Table 1.

(Comparative Example 2)
In the same manner as in Example 1 except that cyclohexane and normal rich butane were charged when the total amount of unreacted residual monomers contained in the resin particles reached 3% by weight, expandable methyl methacrylate resin particles were Obtained.

  The obtained expandable methyl methacrylate resin particles were evaluated by classification, preliminary foaming and molding in the same manner as in Example 1. The evaluation results were as shown in Table 1.

(Comparative Example 3)
The same procedure as in Example 1 was conducted except that cyclohexane and normal rich butane were charged when the total amount of unreacted residual monomers contained in the resin particles reached 50% by weight.

  After charging cyclohexane and normal rich butane, the suspended state became unstable, the reaction could not be completed, and expandable methyl methacrylate resin particles for evaluation could not be obtained.

Claims (5)

  An expandable methyl methacrylate resin particle, wherein an average chord length of a cut cell of a molded product obtained by foaming an expandable methyl methacrylate resin particle is 70 µm or more and 200 µm or less.   A monomer component composed of a methyl methacrylate monomer and a polyfunctional monomer having a molar ratio of 0.02 vinyl group to 0.20 vinyl group with respect to the methyl methacrylate monomer. 2. The expandable methyl methacrylate resin particles according to claim 1, which are obtained by impregnating a methyl methacrylate resin particle having a weight average molecular weight of 250,000 or more and 500,000 or less obtained by polymerization with a foaming agent.   A foam-molded product obtained by foam-molding the foamable methyl methacrylate resin particles according to claim 1 or 2.   A foaming methyl methacrylate resin particle comprising: polymerizing a methyl methacrylate monomer, and adding a foaming agent when the total residual monomer amount is 5% by weight or more and 20% by weight or less. Production method.   A monomer component composed of 0.02 vinyl group mol% to 0.20 vinyl group mol polyfunctional monomer is polymerized with respect to methyl methacrylate monomer and methyl methacrylate monomer. The foaming methyl methacrylate resin particles according to claim 4, wherein a foaming agent is added when the total residual monomer amount is 5 wt% or more and 20 wt% or less.