JPH0770255A - Core-shell polymer - Google Patents

Abstract

PURPOSE:To produce a polyacetal resin molding having a surface excellent in matte visual appearance free from pockmarks without reducing the mechanical properties, electrical properties, etc., of the polyacetal resin. CONSTITUTION:A core-shell polymer, composed of an alkyl acrylate-based rubbery core part and a methyl methacrylate-based glass-state shell part, and a polyacetal resin composition prepared by blending the core-shell polymer with polyacetal resin are obtained. This core-shell polymer is characteristically synthesized by controlling the polymerization of the shell part so that the conversion of the monomer to the polymer may be <=80% at a point of time when addition of the monomer is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a core-shell polymer having no surface pockmark and capable of effectively reducing surface gloss, a method for producing the same, and a polyacetal resin composition obtained by kneading and blending the core-shell polymer.

[0002]

2. Description of the Related Art Polyacetal resins have recently been used in an extremely wide range of fields as engineering plastics which are characterized by high elastic modulus and sliding characteristics and which are excellent in mechanical properties, electrical properties, chemical resistance and heat resistance. ing. In these fields, for example, in the use of interior parts of automobiles, a matte appearance with low gloss is required for the purpose of suppressing irritation to the eyes due to reflection of light or giving a high-grade feeling. However, since the polyacetal resin has a better surface gloss than other general resin materials, in particular, in a product in which various resin materials are compounded, it is not possible to harmonize with other matting materials and the surface appearance is In many cases, the use of what is important is restricted. In order to solve such a problem, a method of adding calcium carbonate, talc, or the like to a polyacetal resin has been conventionally known, and the inventors have made a polyacetal resin a core-shell polymer having an oxygen-containing polar group in the shell part. Improvements such as reducing the gloss of the polyacetal resin molded product have been made by adding it (JP-A-5-27136).
1).

[0003]

However, in the former method, it is necessary to add a large amount of calcium carbonate, talc or the like in order to obtain the required matting effect. Impact resistance tends to decrease. In addition, although the latter method has a sufficient matting effect,
There is a problem that some dents are scattered on the surface of the molded product (pockmarks are seen).

[0004]

[Means for Solving the Problems] The inventors of the present invention have conducted diligent research to develop a polyacetal resin composition which gives a matte appearance without patter on the surface of a molded article without impairing the original properties of the polyacetal resin. As a result of the repetition, the present invention has been completed. That is, the present invention comprises a core shell comprising an alkyl acrylate-based rubber-like core portion and a methyl methacrylate-based glass-like shell portion, and the conversion of the shell portion into a polymer at the end of addition of a monomer is 80% or less during polymerization. The present invention provides a polymer, a method for producing the same, and a polyacetal resin composition which gives a matte appearance without patter on the surface of a molded article obtained by kneading and blending the core-shell polymer with a polyacetal resin.

The core-shell polymer consisting of the alkyl acrylate rubber-like core portion and the methyl methacrylate glass-like shell portion in the present invention is such that the polymer of the previous stage is sequentially coated in the presence of the polymer of the previous stage. It is obtained by a continuous multistage emulsion polymerization method, a so-called seed emulsion polymerization method. The seed emulsion polymerization method is a method of producing a core-shell polymer by first preparing a seed latex, obtaining a core latex by seed polymerization in the presence of the seed latex, and then repeating seed polymerization in the presence of the core latex. . The seed latex is
The surfactant and water are added to the reactor, the temperature is raised, and then the monomers corresponding to the required characteristics are added all at once, and then the polymerization initiator is added to carry out emulsion polymerization, whereby the adjustment is carried out. Methyl methacrylate, ethyl acrylate and the like are preferably used as the monomer. Polymerization of the alkyl acrylate-based rubber-like core portion is performed by emulsion-polymerizing the alkyl acrylate-based monomer in the presence of the seed latex. As the alkyl acrylate-based monomer, an alkyl acrylate having an alkyl group having 2 to 8 carbon atoms or the alkyl acrylate and a monomer copolymerizable therewith are preferably used. In this case, it is desirable to use a crosslinkable monomer and / or a grafting monomer.

Examples of the alkyl acrylate having 2 to 8 carbon atoms in the alkyl group include ethyl acrylate, propyl acrylate, butyl acrylate, cyclohexyl acrylate and 2-ethylhexyl acrylate. Butyl acrylate is preferably used. Examples of the monomer copolymerizable with the alkyl acrylate include, for example, styrene, vinyltoluene, aromatic vinyl such as α-methylstyrene, aromatic vinylidene, acrylonitrile, vinyl cyanide such as methacrylonitrile, vinylidene cyanide, and methyl methacrylate. Examples thereof include alkyl methacrylate such as butyl methacrylate. Further, as the crosslinkable monomer,
For example, aromatic divinyl monomer such as divinylbenzene,
Ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, trimethylolpropane dimethacrylate Examples thereof include alkane polyol polyacrylates such as methylol propane triacrylate and trimethylol propane trimethacrylate, and alkane polyol polymethacrylates. Butylene glycol diacrylate,
Hexanediol diacrylate is preferably used.

Examples of the grafting monomer include unsaturated carboxylic acid allyl esters such as allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate and diallyl itaconate. Allyl methacrylate is preferably used.
Such a crosslinkable monomer and a grafting monomer each account for about 0.05 to 2 of the total amount of the core latex monomer.
It is used in the range of weight%, preferably about 0.1 to 1 weight%. The obtained core polymer is a rubber-like polymer having a glass transition temperature of preferably -30 ° C or lower. When the glass transition temperature exceeds -30 ° C, the impact resistance of the molded product obtained by melt blending with the polyacetal resin may not be improved in some cases. The weight ratio of the core latex is preferably in the range of 40 to 70% by weight based on the whole core shell polymer. When the amount is less than 40% by weight, the impact resistance of the molded product obtained by melt blending with the polyacetal resin is lowered, and when it exceeds 70% by weight, the impact resistance is improved, but the bending elastic modulus is lowered. There is. Polymerization of the methyl methacrylate-based glassy shell portion to be performed next is carried out by emulsion-polymerizing the methyl methacrylate-based monomer in the presence of the core latex. As the methyl methacrylate-based monomer, methyl methacrylate, or the methyl methacrylate and a monomer copolymerizable therewith are preferably used.

Examples of the monomer copolymerizable with the methyl methacrylate include alkyl acrylates such as ethyl acrylate and butyl acrylate, alkyl methacrylates such as ethyl methacrylate and butyl methacrylate, aromatic vinyl such as styrene and α-methylstyrene, and aromatics. Examples thereof include vinyl cyanide such as vinylidene group, acrylonitrile and methacrylonitrile, and vinyl polymerizable monomers such as vinylidene cyanide. Ethyl acrylate, styrene or acrylonitrile are preferably used. Also in the polymerization of the shell part, if necessary, a small amount of a crosslinkable monomer may be used as a copolymerization monomer in addition to the above-mentioned monomer, and thus a higher impact resistance can be imparted to the thermoplastic resin. In some cases a core-shell polymer can be obtained. In this case, the crosslinking monomer may be the same as that used in the polymerization for forming the core, and
Such a crosslinkable monomer is generally used in the range of 0.01 to 2% by weight, preferably 0.1 to 1% by weight, based on the total amount of monomers used for the polymerization of the shell part. The glass transition temperature of the obtained shell polymer is preferably 60 ° C.
It is the above glassy polymer. Glass transition temperature is 60
If the temperature is lower than 0 ° C, the workability during melt blending with the polyacetal resin may deteriorate.

In the production of the core-shell polymer according to the present invention, as the polymerization initiator used in the emulsion polymerization of the above-mentioned various monomers, azobisisobutyronitrile, 2,
2'-azobis (2-amidinopropane) dihydrochloride,
Azo-based polymerization initiators such as 2,2′-azobis (2- (2-imidazolin-2-yl) propane) and dimethyl methylpropaneisobutyrate, and organic peroxides such as cumene hydroperoxide and diisopropylbenzene hydroperoxide A system initiator can be mentioned. Further, as the surfactant used for the polymerization, ether type such as polyoxyethylene nonylphenyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, ester type such as polyoxyethylene monostearate, polyoxyethylene sorbitan mono Widely used nonionic surfactants such as sorbitan ester type such as laurate and block polymer type such as polyoxyethylene polyoxypropylene block copolymer are preferably used. In the present invention, the addition amount of the surfactant is appropriately selected depending on the particle stabilizing ability of the surfactant. When a persulfate-based initiator or a surfactant containing a sulfate ion is used, the initiator or surfactant remaining in the core-shell polymer has a bad influence on the thermal stability of the polyacetal resin composition. There are cases.

The polymerization of the shell part is considerably faster than the usual polymerization of the shell part by using a monomer emulsion or a monomer solution prepared by sufficiently emulsifying a mixture of the above-mentioned monomer, surfactant and, if necessary, deionized water. Continuously add dropwise at the addition rate. At the end of the addition of the monomer emulsion, the rate of conversion of the monomer to the polymer, that is, the conversion rate is measured. When the conversion rate is 80% or less, preferably 70% or less, and more preferably 60% or less, the obtained molded article of the polyacetal resin composition containing the core-shell polymer has a surface-free gloss. An erased appearance is obtained. Here, the conversion rate of the shell portion into the polymer at the end of addition of the monomer is determined as follows. First, calculate the conversion rate of the core part according to the following equation (1).

[Equation 1] In the seed emulsion polymerization method, the residual monomer is usually reduced as much as possible, and the conversion is often performed at a high conversion rate of 90% or more so that the calculated particle size is obtained. However, with the core-shell polymer composed of the composition according to the present invention, even if the conversion rate is less than 90%, the surfactant and the monomer are sufficiently emulsified, or the monomer and the surfactant form a uniform solution. By doing so, the particle size as calculated can be obtained. In the present invention, the conversion rate is preferably 20% or more.
If it is less than 20%, the polymerization stability may deteriorate.
The core-shell polymer latex thus obtained can be taken out in the form of granules, flakes or powder by freeze-thawing or separating the polymer by salting out, followed by centrifugal dehydration and drying. Spray drying with a spray dryer is also a suitable method for removing the core shell polymer from the latex. The core-shell polymer thus taken out may be further shaped into pellets by an extruder or a pelletizer, if necessary. Further, as it is, it can be melt-mixed with a thermoplastic resin as a matting agent and an impact resistance agent.

The polyacetal resin used in the present invention is a polymer compound having an oxymethylene group (--CH ₂ O--) as a main constituent unit. In addition to polyoxymethylene homopolymers, polyoxymethylene copolymers and oxymethylene groups, other polyacetal resins are used. It may be a copolymer, terpolymer, or block copolymer containing a small amount of structural units, and the molecule may have not only a linear structure but also a branched or crosslinked structure. Further, there is no particular limitation on the degree of polymerization thereof. The addition amount of the core-shell polymer of the present invention to 100 parts by weight of the polyacetal resin is 1 to 20 parts by weight, preferably 2 to 10 parts by weight. If the amount of the core-shell polymer added is less than 1 part by weight, the matting effect of the obtained molded article may not be sufficiently exhibited, and if it exceeds 20 parts by weight, the impact resistance is improved but the rigidity and heat resistance are reduced. There are cases. It is desirable to add various known stabilizers to the composition of the present invention to further improve thermal stability. For this purpose, known antioxidants, nitrogen-containing compounds, alkali or alkaline earth metal compounds are added to the composition. It is desirable to use two or more types in combination. Further, a flame retardant, a release agent, a weather resistance imparting agent, an antistatic agent, a heat resistance imparting agent, a coloring agent, a reinforcing agent, a surfactant, an inorganic filler, a lubricant and the like may be added.

In the melt-kneading of the polyacetal resin, the core-shell polymer of the present invention is not loosened and dispersed in the primary particles but is dispersed in secondary particles of about 0.5 to 2.0 μm. . The reason for this is that under the conditions (temperature and shear rate) of usual melt blending of the core-shell polymer and the polyacetal resin, 0.5-
It is considered that the secondary particles having a size of about 2.0 μm are easily disentangled, and the secondary particles having the size are likely to cause slipping, that is, flow. Therefore, the surface of the molded product also has microscopic irregularities of about 0.5 to 2.0 μm, and the irregularities diffusely reflect light to reduce the surface gloss and provide a matte appearance. Furthermore, since the dispersed secondary particles are uniformly dispersed within the range of 0.5 to 2.0 μm, it is possible to obtain a molded product having no patter on the surface.

[0013]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.
In the following Examples and Comparative Examples, all "parts" indicate parts by weight. The abbreviations used in the examples and comparative examples are as follows. Monomer Butyl Acrylate BA 2-Ethylhexyl Acrylate 2EHA Styrene St Methyl Methacrylate MMA Ethyl Acrylate EA Methacrylic Amide MAM 1,4-Butylene Glycol Diacrylate BGA Allyl Methacrylate ALMA Hydroxy Ethyl Methacrylate HEMA Nonionic Surfactant Polyoxyethylene Nonyl Phenyl Ether Kao ( Emulgen 950 E950 manufactured by Kao Emulgen 985 E985 manufactured by Kao Co., Ltd. Other deionized water DIW azo polymerization initiator 2,2′-azobis (2- (2-imidazolin-2-yl) propane) (Wako Pure Chemical Industries, Ltd. ) VA-061) VA-061 2,2'-azobis (2-amidinopropane) dihydrochloride (Wako Pure Chemical Industries, Ltd. V-50) V-50

Example 1 (Production of core-shell polymer A) DI was placed in a 10 liter polymerization vessel equipped with a reflux condenser.
W 1500 g and 10% E950 aqueous solution 75.0 g were charged, and the temperature was raised to 70 ° C. with stirring under a nitrogen stream.
To this, 75.0 g of EA was added and dispersed for 10 minutes, then 6.0 g of 10% V50 aqueous solution was added, and stirred for 1 hour to prepare a seed latex. Subsequently, the seed latex was heated to 75 ° C., and VA-0 was added thereto.
61 1.38 g was added, and further, a monomer emulsion for forming the following core was continuously fed over 200 minutes,
Seed polymerization was performed. Monomer emulsion for core formation 2EHA 922.7g BA 247.4g ALMA 2.5g BGA 2.5g 10% E950 750.0g DIW 3750.0g After feeding the monomer emulsion as described above, raise to 90 ° C. After warming and aging for 1 hour, it was cooled to 70 ° C. and polymerized to form a shell. That is, VA-06
1 1.25 g was added, and the following monomer emulsion was added to 40
The seeds were polymerized to form a shell with continuous feed over minutes. Monomer Emulsion for Shell Formation MMA 1056.3g EA 125g St 62.5g MAM 6.3g 10% E985 250g DIW 500g After feeding this monomer emulsion, the conversion was measured.
The conversion rate was 58%. Next, the temperature was raised to 75 ° C., the mixture was aged for 1 hour, cooled, and filtered through a 300-mesh stainless wire mesh to obtain a core-shell polymer latex. The latex was frozen at −30 ° C., dehydrated and washed with a centrifuge, and then air-dried at 60 ° C. for 24 hours to obtain a core-shell polymer A.

Examples 2 and 3 Core-shell polymers B and C having the compositions shown in Table 1 were obtained by the same procedure as in Example 1. Example 4 (Production of polyacetal resin composition (1)) Polyplastics Co., Ltd. polyacetal resin DURACON M90-31 90 parts and core shell polymer A 10 parts produced in Example 1 were manufactured by Ikegai Tekko KK Using a twin-screw extruder PCM-30, a cylinder temperature of 220 ° C,
Melt mixing was performed at a die head temperature of 225 ° C. to obtain pellets of the polyacetal resin composition (1). Examples 5 and 6 Using the core-shell polymers B and C shown in Examples 2 and 3, the same operation as in Example 4 was carried out to obtain pellets of the polyacetal resin compositions (2) and (3).

Comparative Example 1 (Production of Core-Shell Polymer D) DI was placed in a 10 liter polymerization vessel equipped with a reflux condenser.
W 2100 g and 10% E950 78.5 g were charged and the temperature was raised to 70 ° C. with stirring under a nitrogen stream. To this, 105 g of EA was added and dispersed over 10 minutes, then 508.3 g of 10% V50 was added and stirred for 1 hour.
A seed latex was prepared. Subsequently, the seed latex was heated to 70 ° C., and 10% V504
6.7 g was added, and further, a monomer emulsion for forming a core described below was continuously fed over 240 minutes to perform seed polymerization. Monomer mixture for core formation BA 2094.1 g MMA 234.5 g BGA 4.7 g ALMA 11.7 g 10% E950 466.7 g DIW 1641.0 g After seed polymerization was carried out as described above, the temperature was raised to 90 ° C. After warming and aging for 1 hour, it was cooled to 70 ° C. and polymerized to form a shell. That is, 10% V50
21 g was added, and the monomer emulsion described below was continuously fed over 180 minutes to perform seed polymerization for forming a shell. Monomer Emulsion for Shell Formation MMA 807.9g HEMA 135.0g EA 105.0g BGA 2.1g 10% E950 26.3g DIW 1650.0g After seed polymerization to form this shell the conversion is It was measured. The conversion rate was 91%. Next, the temperature was raised to 90 ° C., the mixture was aged for 1 hour, cooled, and filtered through a 300-mesh stainless wire mesh to obtain a core-shell polymer latex. The latex was frozen at −30 ° C., dehydrated and washed with a centrifuge, and then air-dried at 60 ° C. for 24 hours to obtain a core-shell polymer D.

Comparative Examples 2 and 3 Core-shell polymers E and F having the compositions shown in Table 1 were obtained by the same procedure as in Example 1. Comparative Examples 4 to 6 (Production of Polyacetal Resins (4) to (6)) Polyacetal resin compositions (4) to (6) using core-shell polymers DF shown in Comparative Examples 1 to 3 according to Example 4
The pellet of (6) was obtained.

Measurement of surface gloss of resin composition and physical property test Resin compositions (1) to (6) and polyacetal resin (Duracon M90-31) were dried at 120 ° C. for 2 hours, and then manufactured by Nissei Resin Co., Ltd. Using the injection molding machine TS-100, the cylinder temperature and the nozzle temperature are 210 ° C. and
A flat plate of 50 mm × 50 mm × 2 mm was molded at a mold temperature of 60 ° C. According to JISK7105, the obtained molded product was measured for surface glossiness at 60 ° -60 ° using a gloss meter Σ80 manufactured by Nippon Denshoku Co., Ltd.
Izod impact value and JISK72 according to K7110
Bending strength and bending elastic modulus were measured in accordance with No. 03. The results are shown in [Table 2].

[0019]

[Table 1] Core / shell ratio 70/30 and core ratio large ALMA (grafting agent) small Shell BGA (cross-linking) technology disclosed in Japanese Patent Application Laid-Open No. 5-271361 without ALMA (grafting agent) Shell portion monomer emulsion continuously over 180 minutes As a result, the conversion rate after feeding was as high as 88%.

[0020]

[Table 2] Physical properties using the core-shell polymer A having a core / shell ratio of 50/50 according to the present invention. Features of matte appearance that is smooth without fluttering As the core / shell ratio is increased to 70/30 and the core ratio is increased, the bending strength and elastic modulus are slightly decreased, the glossiness is increased and the Izod impact value is improved as compared with Example 4. . When the core / shell ratio is 70/30, the amount of grafting agent is reduced,
By adding crosslinking to the shell, the glossiness is further increased, and the bending property is slightly increased as compared with Example 5. Core-shell polymer D according to JP-A-5-271361
The result is that the glossiness is as good as 6.3%, which is excellent, but there is a problem with countless pockmarks of ˜0.1 mm. With the core-shell polymer E containing no grafting agent, although the Izod impact value was good, a pock of ~ 0.1 mm was considerably confirmed. The physical properties of the core-shell polymer F having a high conversion rate are almost the same as those in Example 4. Although it is slightly inferior in terms of glossiness, a pock of ~ 0.1 mm can be confirmed and the surface condition is poor.

[0021]

EFFECTS OF THE INVENTION A molded article obtained by molding a composition obtained by kneading and blending the core-shell polymer of the present invention with a polyacetal resin retains the balanced mechanical properties inherent to the polyacetal resin and has a high thermal stability. It is excellent and has the effect of giving the surface of the molded product a matte appearance without patter. Therefore, the polyacetal resin composition of the present invention can be suitably used in the fields of automobile interior parts, optical instruments, electric instruments and the like.

Claims (11)

[Claims] 1. An alkyl acrylate rubber core,
A core-shell polymer comprising a methylmethacrylate-based glassy shell part, wherein the conversion of the shell part into the polymer at the time of addition of the monomer at the time of polymerization is 80% or less. 2. An alkyl acrylate-based rubber-like core portion,
A polymer of an alkyl acrylate having an alkyl group having 2 to 8 carbon atoms, or a copolymer of the alkyl acrylate and a monomer copolymerizable therewith.
The described core-shell polymer. 3. The core-shell polymer according to claim 1, wherein the methyl methacrylate-based glassy shell portion is a polymer of methyl methacrylate or a copolymer of the methyl methacrylate and a monomer copolymerizable therewith. 4. The core-shell polymer according to claim 1, wherein the core portion contains a crosslinking agent and a grafting agent. 5. The core-shell polymer according to claim 1, wherein the glass transition temperature of the core part is −30 ° C. or lower, and the glass transition temperature of the shell part is 60 ° C. or higher. 6. The core-shell polymer according to claim 1, wherein the weight of the core part is 40 to 70% by weight based on the whole core-shell polymer. 7. An alkyl acrylate rubber core,
A method for producing a core-shell polymer, which comprises forming a methyl methacrylate-based glassy shell portion by emulsion polymerization, and converting the shell portion to a polymer at the end of addition of the monomer at the time of polymerization of 80% or less. 8. The method for producing a core-shell polymer according to claim 7, wherein an azo initiator and a nonionic surfactant are used. 9. A polyacetal resin composition containing the core-shell polymer according to claim 1. 10. A core-shell polymer according to claim 1
The polyacetal resin composition according to claim 9, wherein the polyacetal resin composition comprises 20 to 20 parts by weight. 11. A polyacetal resin molded product obtained by molding the resin composition according to claim 9.