JP2001233986A - Foamable methyl methacrylate based resin particle, its manufacturing method, and foam using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide foamable methyl methacrylate based resin particles having reduced gas leakage in foam molding, uniform foamed cells at a high expansion ratio, and good moldability, excellent process productivity, and additionally excellent mechanical strength and useful as cushioning packaging materials, thermal insulating materials, and civil engineering materials. SOLUTION: The foamable methyl methacrylate based resin particles are obtained by polymerizing a monomer component comprising 70-100 pts.wt. methyl methacrylate monomer units, 0-30 wt.% other monofunctional unsaturated monomer units copolymerizable therewith, and 0-0.2 vinyl group mol% polyfunctional monomer to obtain methyl methacrylate based resin particles having a weight average molecular weight of 250,000-800,000 and impregnating the particles with a blowing agent, and these particles are used in manufacturing foams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable methyl methacrylate resin particles and to a methyl methacrylate resin foam using the same. More specifically, the present invention relates to expandable methyl methacrylate-based resin particles having a high expansion ratio, uniform foam cells, and good moldability, and a methyl methacrylate-based resin foam having a good appearance and excellent mechanical strength using the same. . Further, the present invention relates to a methyl methacrylate-based resin foam which emits little smoke when ignited and is suitable for use in vanishing models and building structures used in metal casting.

[0002]

2. Description of the Related Art Foaming of a methyl methacrylate polymer is generally difficult, elongational viscosity and shear viscosity upon melting are not suitable for foaming behavior, and the ability to retain air bubbles is insufficient. For this reason, not only does not foam sufficiently, but also the foam cells become non-uniform, the surface of the obtained foam has many irregularities, and it is difficult to form a smooth surface. It was difficult to obtain a foam. JP-A-50-127990 discloses that thermoplastic polymer particles are suspended in water containing a dispersing agent for controlling the particle size,
The methacrylic acid ester-based monomer is added dropwise to the thermoplastic polymer under a polymerization initiator so as to have a specific ratio to the thermoplastic polymer and polymerized, thereby reducing the unevenness of the molecular weight distribution of the obtained polymer particles. A method for optimizing the foaming performance is disclosed. As foaming of a methyl methacrylate polymer, there has been proposed a foamed plate which does not melt and flow and is obtained by cast polymerization or the like in order to increase elongational viscosity. Japanese Patent Laid-Open No. 4-28320 discloses a method for reducing soot.
No. 9 discloses foaming resin particles in which the proportion of an aromatic vinyl compound is reduced.

[0003]

However, Japanese Patent Application Laid-Open No. 50-127990 and Japanese Patent Application Laid-Open No. 4-28320 are not disclosed.
The resin described in Japanese Patent Publication No. 9 does not always have sufficient foaming performance. In view of such circumstances, the present inventor has proposed that a foam comprising a methyl methacrylate-based resin composition which is a polymer having a specific molecular weight and heat resistance and which has been polymerized using a specific amount of a polyfunctional monomer, With high expansion ratio during foaming and foam molding,
The present inventors have found that a foam having uniform foam cells and a good appearance can be obtained, and have reached the present invention.

[0004]

That is, the present invention relates to a method for preparing 70 to 100% by weight of methyl methacrylate monomer units and 0 to 30% by weight of other monofunctional unsaturated monomer units copolymerizable therewith. Functional monomer 0 to 0.2 vinyl group mol%
And a foamable methyl methacrylate-based resin particle obtained by impregnating a blowing agent into a methyl methacrylate-based resin particle having a weight average molecular weight of 250,000 to 800,000, which is obtained by polymerizing a monomer component consisting of is there. Hereinafter, the present invention will be described in detail.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The resin composition of the present invention comprises 70 to 100% by weight of a methyl methacrylate monomer unit and 0 to 100% of another monofunctional unsaturated monomer unit copolymerizable therewith. 30% by weight and 0 to 0.2 vinyl group mol% of the polyfunctional monomer. Examples of the copolymerizable monofunctional unsaturated monomer include methacrylates such as ethyl methacrylate, propyl methacrylate, butyl methacrylate, and benzyl methacrylate; methyl acrylate,
Acrylic esters such as ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride, etc. Acid anhydrides of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, monoglycerol acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, monoglycerol methacrylate and the like; esters containing acrylamide; There are methacrylamide and diacetone acrylamide. Nitriles include acrylonitrile, methacrylonitrile, diacetone acrylamide, nitrogen-containing monomers such as dimethylaminoethyl methacrylate; allyl glycidyl ether, glycidyl acrylate, epoxy-containing monomers such as glycidyl methacrylate; styrene, Styrene-based monomers such as α-methylstyrene are exemplified.

[0006] In particular, those having a composition range of 70% by weight or more of methyl methacrylate, 0 to 10% by weight of vinyl aromatic hydrocarbon, and 0 to 30% by weight of methacrylate or acrylate other than methyl methacrylate are preferable. . In order to further reduce soot, a monomer having a composition in the range of 0 to 30% by weight of a monomer selected from acrylates and methacrylates is more preferable as a copolymerizable monofunctional monomer.

When the content exceeds 10% by weight of the vinyl aromatic hydrocarbon,
In the case where the resin is used for a vanishing model for casting or the like, there are disadvantages such as carbon residue remaining when the resin is burned and the casting surface becomes rough. In addition, methacrylates or acrylates other than methyl methacrylate undergo internal plasticization to facilitate foaming. However, if the content exceeds 30% by weight, the heat resistance of the obtained resin is reduced, and shrinkage after foam molding is reduced. This is not preferable, and the weather resistance, low combustion heat resistance, and heat resistance, which are characteristics of the methyl methacrylate polymer, are hardly exhibited.

[0008] The weight average molecular weight (Mw) of the methyl methacrylate resin composition of the present invention is 250,000 to 800,000, preferably
300,000 to 600,000.

[0009] If the Mw is less than 250,000, the mechanical strength of the foam obtained by foam molding the resin is not sufficient, and if it exceeds 800,000, the foaming property is undesirably reduced.

[0010] The weight average molecular weight Mw is a value determined by gel permeation chromatography (GPC) and a differential refractometer based on standard PMMA data. This method is described in, for example, the 1984 edition “Polymer Characteristic Analysis”.
(Kyoritsu Shuppan) pages 24 to 55.

[0011] The methyl methacrylate resin of the present invention comprises the above-mentioned monofunctional unsaturated monomer, a polyfunctional constituent unit containing a polyfunctional monomer, a chain transfer agent if necessary, and / or It is obtained by adding a polymerization initiator and polymerizing. As a component serving as a polyfunctional structural unit, a polyfunctional monomer has a large effect, but a polyfunctional chain transfer agent, a polyfunctional initiator, and a mixture thereof are given as those having a similar effect. Can be.

As for the amount of the polyfunctional monomer to be added, the larger the amount of the added, the better the foaming performance. It is preferable not to add more. Here, the vinyl group mol% is a unit in which the equivalent of the functional group is represented by%.

Examples of the copolymerizable polyfunctional monomer include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol di (meth) acrylate. Ethylene glycol or its oligomer, in which both terminal hydroxyl groups are esterified with acrylic acid or methacrylic acid; divalent such as neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, butanediol di (meth) acrylate Alcohol hydroxyl groups esterified with acrylic acid or methacrylic acid; polyhydric alcohols such as trimethylolpropane, pentaerythritol or derivatives of these polyhydric alcohols are esterified with acrylic acid or methacrylic acid And aryl compounds having two or more alkenyl groups such as divinylbenzene.

[0014] As the chain transfer agent, a well-known one used for polymerization of methyl methacrylate may be used. These include monofunctional chain transfer agents having one chain transfer functional group and polyfunctional chain transfer agents having two or more chain transfer functional groups. Examples of the monofunctional chain transfer agent include alkyl mercaptans and thioglycolic acid esters, and examples of the polyfunctional chain transfer agent include ethylene glycol, neopentyl glycol, trimethylolpropane, ditrimethylolpropane, pentaerythritol, Polyhydric alcohols such as pentaerythritol, tripentaerythritol, sorbitol, etc.
-Esterified with mercaptopropionic acid.

The amount of the chain transfer agent used for the polymerization of the methyl methacrylate resin composition is usually 5 × 10 ⁻⁵ mol to 5 × 10 ⁻³ mol per 1 mol of the monofunctional unsaturated monomer. Yes,
The number of functional groups of the polyfunctional monomer is 0 to 0.2 vinyl group mol
%, The molecular weight is adjusted, and an appropriate amount is used to obtain a target molecular weight.

[0016] The weight average molecular weight of the methyl methacrylate resin composition is generally governed mainly by the concentration of the polyfunctional monomer, the concentration of the chain transfer agent and the concentration of the radical initiator. Adjusting the polymerization average molecular weight, the higher the concentration of the polyfunctional monomer, the higher the polymerization average molecular weight, and conversely, the lower the concentration of the chain transfer agent, the smaller the concentration of the polyfunctional monomer. It is carried out by appropriately changing the concentration of the chain transfer agent within the range.

The polymerization initiator includes a monofunctional polymerization initiator that generates one pair of radicals in one molecule and a polyfunctional polymerization initiator that generates two or more pairs of radicals. As the monofunctional polymerization initiator, for example, 2,2′-azobis (2,4-
Azo compounds such as dimethylvaleronitrile), azobisisobutyronitrile and dimethyl-2,2'-azobisisobutyrate; t-butylperoxypivalate, t-butylperoxy-2-ethylhexanoate, cumylperoxy Peroxyesters such as 2-ethylhexanoate; organic peroxides of diacyl peroxides such as di-3,5,5-trimethylhexanoyl peroxide and dilauroyl peroxide; and the like. Examples of the polyfunctional polymerization initiator include bifunctional 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane and di-t-butylperoxytrimethyladipate. -(T-butylperoxy) triazine and tetrafunctional 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane.

As a polymerization method for obtaining the methyl methacrylate resin composition of the present invention, a well-known polymerization method for producing a general methyl methacrylate resin can be applied. That is, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method. Above all, a method of polymerizing methyl methacrylate-based resin particles by suspension polymerization is preferable because the pelletization step can be omitted, so that there is no thermal decomposition of the resin and the merit is large in terms of cost.

Furthermore, the Vicat softening temperature (VST) of the methyl methacrylate-based resin composition of the present invention is 100 ° C. to Δ110 + 50 × the amount of the polyfunctional monomer (vinyl) with respect to the content of the polyfunctional monomer. Mol%)｝ ° C., preferably 10
0 ° C. to (107 + 65. Polyfunctional monomer amount (vinyl group m
ol%)) It is possible to exhibit better foaming performance by adjusting to the range of ° C.

When the amount of the polyfunctional monomer added is small or not added, the VST is reduced by changing the copolymer composition ratio and the type of the monomer to be copolymerized during prefoaming, and the internal plasticization is carried out. It is necessary to facilitate foaming. However, if VST is lower than 100 ° C., VST higher than 100 ° C. is preferable because it is easily shrunk by steam vapor at the time of prefoaming and also has poor moldability. On the other hand, when the amount of the polyfunctional monomer is small or no addition, if the VST is too high, the foaming property and the moldability deteriorate, and the addition of the polyfunctional monomer results in # 11.
It is more preferable that the VST is 0 + 50 × the amount of polyfunctional monomer (vinyl group mol%)｝ or less.

VST is the value of the Vicat softening temperature obtained by the method A of JIS K7206. The sample used for the measurement is a value in which the unreacted residual monomer is 0.5% or less and a polymer in a state in which a plasticizer is not added is used.

The methyl methacrylate resin composition of the present invention may contain, if necessary, a releasing agent, an ultraviolet absorber, a coloring agent, an antioxidant, a heat stabilizer, a plasticizer, a flame retardant, and an antistatic agent. Various agents that can be added to a typical acrylic resin can be contained.

The volatile volatile blowing agent used in the present invention includes aliphatic hydrocarbons such as propane, butane and pentane (deleted, hexane); alicyclic hydrocarbons such as cyclobutane and cyclopentane (deleted: cyclohexane); Examples include fluorocarbons having zero ozone depletion potential such as difluoroethane and tetrafluoroethane, and carbon dioxide. These can be used alone or in combination of two or more. The content of the foaming agent is 3
% By weight-12% by weight. If it is less than 3% by weight, the expansion ratio is low, which is not preferable. On the other hand, if it exceeds 12% by weight, the molding cycle becomes undesirably long.

As a method for impregnating the foaming agent, there is a method in which the polymer resin particles are suspended in an aqueous medium, and the foaming agent is pressed and impregnated. When polymerizing polymer resin particles by suspension polymerization, they may be added during the polymerization step or may be added after the polymerization step. Further, the polymer resin particles and the foaming agent may be melt-mixed using an extruder.

Examples of the foaming aid used in the present invention include hydrocarbons having a boiling point of 50 ° C. or higher, and include aliphatic hydrocarbons such as hexane and alicyclic hydrocarbons such as cyclohexane. These can be used alone or in combination of two or more. Its content is 0.3-2% by weight. If it is less than 0.3% by weight, the foaming rate is low, which is not preferable. On the other hand, if it exceeds 2% by weight, the molding cycle becomes undesirably long.

In the present invention, toluene, ethylbenzene,
Aromatic hydrocarbons such as xylene or esters such as dioctyl phthalate and dioctyl adipate can be used as the plasticizer. The content of the plasticizer is 0.
3 to 2% by weight. If it is less than 0.3% by weight, the foaming rate is low, which is not preferable. On the other hand, if it exceeds 2% by weight, the molding cycle becomes undesirably long.

The method for foaming the methyl methacrylate resin composition of the present invention to form a foam is not particularly limited,
For example, a method of melt-kneading a decomposition-type foaming agent and a methyl methacrylate-based resin composition with an extruder and foaming, melting the methyl methacrylate-based resin composition with an extruder, and directly pressing the evaporating foaming agent from the middle of the cylinder. Injecting, kneading, foaming method, the pellets or beads made of the methyl methacrylate resin are impregnated with an evaporating foaming agent in an extruder or an aqueous suspension, and the impregnated pellets or beads are heated with steam or the like. A foaming method may be used.

[0028]

The methyl methacrylate-based resin particles of the present invention and the methyl methacrylate-based resin foam using the same have less outgassing during foam molding, a high expansion ratio, uniform foam cells, It has good moldability, excellent processing productivity, and excellent mechanical strength, and is useful as a cushioning packaging material, a heat insulating material, and a material for civil engineering. Furthermore, the methyl methacrylate-based resin foam of the present invention can reduce the content of vinyl aromatic hydrocarbons, emits little smoke when ignited, and is a vanishing model used in metal casting. Suitable for use on buildings and structures.

[0029]

The present invention will be described below by way of examples. In addition, among the measurement evaluation methods, the items other than the items described above were implemented as follows.

* Expandability 10 g of expandable beads were foamed under normal pressure for 3 minutes using a boiling steamer, and the bulk ratio was measured the next day. [Ml / 10g] * Moldability Five levels (0.0%) of molding pressure with a Daisen KR-57 molding machine
59Mpa, 0.069Mpa, 0.079Mpa,
0.089 MPa, 0.099 MPa), and the surface smoothness at each pressure was evaluated. A: 3 or more at 4 levels or more B: 3 or more at 3 levels C: 3 or more at 2 levels or less * Surface smoothness The amount of particle gaps on the surface of the molded product was visually evaluated. 5 when there is no particle gap, and 1 when there are many particle gaps, 5
It was evaluated on a scale. A score of 3 or more was accepted. * Bending strength A 20 mm flat plate with a sample thickness of JIS A9
Measured according to 511. * Styrene resistance A foam of about 40 times was immersed in styrene for 3 minutes at room temperature, and the volume reduction rate was measured. ○ 90% or more △ 30-90% × dissolution ~ 30%

[0031] Abbreviations of various monomers and chain transfer agents used in the examples are as follows. MMA: methyl methacrylate MA: methyl acrylate CHMA: cyclohexyl methacrylate DDSH: n-dodecyl mercaptan HXA: 1,6-hexanediol diacrylate

Reference Examples A1 to A4, B1 to B5 MMA, MA, HXA and DDSH were added to a 200 liter autoclave equipped with a rotary stirrer in the amounts shown in Table 1 and 2,2 azobis (2,4 dimethyl) valeronitrile. 0.03% by weight, t-butyl peroxy 2-ethylhexanoate 0.025 part by weight, ion exchange water 150 parts by weight, sodium polymethacrylate (1% aqueous solution
Stokes) 0.03 parts by weight / aqueous phase and 2.5 parts by weight of disodium hydrogen phosphate / heptahydrate / aqueous phase are mixed, heated and heated, polymerized at 80 ° C., and polymerized after 120 minutes. Pluronic F68T, an oxyethylene-polyoxypropylene block copolymer (manufactured by Asahi Denka Kogyo Co., Ltd.)
02 parts by weight / water phase were added. Thereafter, polymerization was carried out at the same temperature, and after 60 minutes, a polymerization exothermic peak occurred.
The reaction was performed at 30 ° C. for 30 minutes. After polymerization, washing, dehydration and drying were performed to obtain resin particles having the physical properties shown in Table 1.

[0033] In a 200 L autoclave equipped with a stirrer,
111 parts by weight of ion-exchanged water, tribasic calcium phosphate
8 parts by weight and 0.036 parts by weight of sodium dodecylbenzenesulfonate were added and stirred to form a water suspension, and 100 parts by weight of methyl methacrylate-based resin particles were added.
Temperature. After pressurizing 9 parts by weight of butane (i / n = 60/40), 1 part by weight of toluene and 1 part by weight of cyclohexane, the mixture was heated to 105 ° C., impregnated for 5 hours and 30 minutes, and cooled. The obtained expandable methyl methacrylate-based resin particles were pre-expanded to obtain pre-expanded particles having a bulk factor of 40. The next day, a 20 mm thick flat plate was formed at a vapor pressure of 5 levels, and the formability was evaluated and the bending strength was evaluated. In addition, foaming was performed using a steamer, and the foamability was evaluated.

[0034]

【table 1】 A *: 110 ° C + 50 x Amount of polyfunctional monomer (mol% of vinyl group), Flexural strength Unit kgf / cm ²

Continued on the front page (72) Inventor Takashi Sakamoto 5-1 Sokai-cho, Niihama-shi, Ehime F-term (reference) in Sumitomo Chemical Co., Ltd. 4F074 AA23A AD01 AD02 AD11 AG02 BA32 BA35 BA36 BA37 BA53 CA22 CA32 CA34 CC04X CC10X CC25X 4J100 AB02Q AB03Q AE18Q AJ02Q AJ08Q AJ09Q AL03P AL03Q AL04Q AL08Q AL09Q AL10Q AM02Q AM15Q AM21Q BA03Q BA14Q BA29Q BC43Q BC54Q CA01 CA04 DA01 DA23 FA03 FA04

Claims (7)

[Claims] [Claim 1] 70-1 methyl methacrylate monomer unit
00% by weight and 0 to 30% by weight of other monofunctional unsaturated monomer units copolymerizable therewith and 0 to 0.
Expandable methyl methacrylate-based resin obtained by impregnating a methyl methacrylate-based resin particle having a weight-average molecular weight of 250,000 to 800,000 with a blowing agent, obtained by polymerizing a monomer component comprising 2 vinyl mol%. Resin particles. 2. The expandable methyl methacrylate resin particles according to claim 1, having a weight average molecular weight of 300,000 to 600,000. 3. The expandable methyl methacrylate-based resin particles according to claim 1, wherein the other copolymerizable monofunctional unsaturated monomer comprises a monomer selected from an acrylate ester and a methacrylate ester. 4. The expandable methyl methacrylate resin particles according to claim 1, wherein the plasticizer and / or a foaming aid are impregnated into the methyl methacrylate resin particles together with a foaming agent. . 5. The method according to claim 1, wherein the methyl methacrylate-based resin particles are polymerized by suspension polymerization.
The expandable methyl methacrylate-based resin particles described in the above section. 6. The Vicat softening temperature of the methyl methacrylate-based resin particles is 100% with respect to the content of the polyfunctional monomer.
℃ ~ ｛110 + 50x polyfunctional monomer amount (vinyl group mo
The method for producing expandable methyl methacrylate-based resin particles according to any one of claims 1 to 5, wherein the resin particles having a temperature of 1%)｝ C are impregnated with a blowing agent. 7. A foam obtained by subjecting the expandable methyl methacrylate-based resin particles according to claim 1 to foam molding.