JPH07126483A - Polyacetal resin composition - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a polyacetal resin composition having significantly improved practical impact resistance. [Structure] (A) 100 parts by weight of a polyacetal resin having a crystallization time of 5 minutes or more, and (B) 3 to 50 parts of a thermoplastic polyurethane-based and / or core-shell polymer-based impact modifier.
Add parts by weight.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyacetal resin composition having excellent impact resistance.

[0002]

2. Description of the Related Art Polyacetal resins are excellent in mechanical properties, fatigue resistance, friction / wear resistance, chemical resistance, heat resistance and moldability.
It is widely used in the fields of automobiles, electric and electronic devices, precision machinery, and building material piping. However, with the expansion and diversification of applications, the demand for the quality thereof is becoming more sophisticated. Impact resistance is often cited as a required property, and various methods for imparting impact resistance to polyacetal resins have been proposed. For example, there is a method of adding a polyolefin-based thermoplastic elastomer, which is effective in improving impact resistance. However, these contribute greatly to the improvement of the Izod impact strength, in which the impact acts in a uniaxial direction.However, in the actual destructive tests of molded articles such as various applied parts, the impact characteristics increase as the Izod impact strength improves. Often has not improved. That is, for the actual impact strength of molded parts, it is considered that a resin with improved impact resistance is required not only for uniaxial but also for multiaxial directions, but in general molding methods, the flow of molten resin is always involved. The orientation of the polyacetal resin in the flow direction is inevitable, and the directional expression is inevitable. Further, as a method of reducing the directionality of polyacetal, it is also known to reduce the melt viscosity,
Since this is generally accompanied by a decrease in the molecular weight of the polyacetal, although a slight effect can be seen in the case of the polyacetal resin alone, when the impact resistance is improved with a thermoplastic elastomer or the like, the molecular weight of the polyacetal is rather reduced and The impact resistance is largely deteriorated, and the impact resistance of the composition is deteriorated. As described above, it was very difficult to improve the impact resistance of the polyacetal resin as a practical property.

[0003]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a polyacetal resin exhibiting a crystallization time of a certain value or longer is used, and thus it is significantly practical. The present invention has been completed by discovering that various impact resistance characteristics can be improved. That is, in the present invention, (A) 100 parts by weight of a polyacetal resin having a crystallization time of 5 minutes or more is added with 3 to 50 parts by weight of (B) a thermoplastic polyurethane-based and / or core-shell polymer-based impact modifier. And a polyacetal resin composition having excellent impact resistance.

In the present invention, having a crystallization time above a certain level means that the speed of crystallization from the molten state is slower than a certain value. The use of a polyacetal resin having a slow crystallization rate may improve the impact resistance, especially the practical impact resistance in the multiaxial direction.
It is considered that the orientation that the molten resin receives when it is shaped is loosened due to the slow crystallization rate and the directionality is weakened, but the details are unknown. The crystallization time in the present invention means
Using a heat-compensated DSC (differential scanning calorimeter, for example, DSC7 type manufactured by Perkin Elmer Co.), polyacetal resin
After keeping the temperature at 200 ° C for 5 minutes, cool it down at a rate of 10 ° C / min.
It is the time from the holding start time to the crystallization exothermic peak when the temperature is lowered to ℃ and the temperature is maintained. By adjusting the crystallization time of the resin used in the present invention to 5 minutes or longer, a good resin composition is obtained. If the crystallization time of the polyacetal resin used is shorter than 5 minutes, the effect of improving the impact resistance in the multiaxial direction, which is the object of the present invention, cannot be obtained. The upper limit of the crystallization time is not particularly limited, but if the crystallization time is long, the time until the resin is hardened may be long and the molding efficiency may be lowered.Therefore, the crystallization time of the polyacetal resin used is 500 minutes. The following is preferable. The polyacetal resin having a too long crystallization time can be adjusted by using a crystal nucleating agent such as boron nitride, calcium carbonate or talc.

In the present invention, both a homopolymer and a copolymer can be used as the polyacetal resin, but the oxymethylene unit (-OCH _2- )
Copolymers (including block copolymers) containing as a main constituent unit an appropriate amount of comonomer component are preferable, and particularly, for a polyacetal copolymer obtained by copolymerizing 3 to 30% by weight of comonomer component, the crystallization time is adjusted to 5 minutes or more. It is preferable because it is easy to carry out, and excellent thermal stability and mechanical strength can be maintained. A particularly preferred amount of comonomer is
It is 3 to 20% by weight. In addition, the acetal copolymer,
The molecule may have not only a linear structure but also a branched structure or a crosslinked structure, and the viscosity of the polyacetal resin is not particularly limited as long as it can be molded. The comonomer component used for producing the polyacetal copolymer is not particularly limited, but those having a structure of the following general formula are generally used.

[0006]

[Chemical 1]

(However, R ₁ , R ₂ , R ₃ , and R ₄ are the same or different substituents, and are a hydrogen atom, an alkyl group (having 1 to 5 carbons and 0 to 3 hydrogens being halogens). Atom-substituted, the same shall apply hereinafter) or a halogen-substituted alkyl group, and R ₅ represents a methylene group, an oxymethylene group, a methylene group or an oxymethylene group substituted by an alkyl group or an alkyl halide, respectively. Group (in this case p =
Integer of 0 to _{3), - (CH 2) q} -OCH 2 - (q = 1~4 integer)
Or - a divalent group represented by (q = 1 to 4 integer) (in this case p = 1) - (O- CH 2 -CH 2) q -OCH 2. ) Examples of the comonomer include ethylene oxide, epichlorohydrin, 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal,
Examples include 1,3-dioxane and propylene oxide. Among them, at least one selected from ethylene oxide, 1,3-dioxolane, diethylene glycol formal, and 1,4-butanediol formal,
It is preferable because the crystallization time can be easily adjusted to a desired range.

Impact modifiers used in the present invention are thermoplastic polyurethanes and / or core shell polymers. Thermoplastic polyurethane has relatively good affinity with polyacetal as compared with other thermoplastic elastomers, and has characteristics such as improved impact resistance and excellent hinge characteristics of the composition. The thermoplastic polyurethane used in the present invention is basically an isocyanate compound and has a molecular weight of 62-
350 short-chain polyols with a soft weight of 4
It is a copolymer composed of 00-5000 long-chain polyols. Particularly preferably, a thermoplastic polyurethane having a glass transition temperature of −15 ° C. or lower is used. The glass transition temperature of thermoplastic polyurethane is usually defined as the peak of loss modulus obtained by a dynamic viscoelasticity measuring device. Examples of the dynamic viscoelastic device include Rheovibron manufactured by Orientec Co., Ltd. When the glass transition temperature is low, the toughness of the thermoplastic polyurethane becomes high, and accordingly, the impact resistance of the composition mixed with the polyoxymethylene resin is improved. Examples of the isocyanate compound constituting the thermoplastic polyurethane include diphenylmethane diisocyanate, 2,4- and 2,6-tolylene diisocyanate, m
-And p-phenylene diisocyanate, hexamethylene diisocyanate and the like are preferably used. As the short-chain polyol component, 1,2-ethanediol, 1,2-
Propanediol, 1,4-butanediol, butenediol, 1,6-hexanediol, 1,10-decamethylenediol and the like are preferably used. Further, the long-chain polyol as the soft component is preferably polyalkylene adipate, polyalkyl ether or the like, more preferably polyethylene-butylene adipate, polybutylene adipate, polynonanediol adipate, polymethylpentene adipate, polytetramethylene glycol or the like. Each of the components may be preferably used alone or as a mixture of two or more.

The core-shell polymer used in the present invention is a polymer having a rubber-like polymer core and a glass-like polymer shell. Since this core-shell polymer is not thermoplastic but is in the form of particles, it is characterized in that it is dispersed in polyacetal uniformly and very finely, and in addition to improved impact resistance, it is characterized by excellent weld characteristics. The core-shell polymer in the present invention is
It is obtained by a continuous multi-step emulsion polymerization method in which the polymer of the previous step is sequentially covered with the polymer of the latter step, so-called seed emulsion polymerization method. Examples of the monomer that constitutes the rubber-like polymer include conjugated dienes, alkyl acrylates in which the alkyl group has 2 to 8 carbon atoms, and mixtures thereof. Examples of such conjugated dienes include butadiene, isoprene, chloroprene, and the like, but butadiene is particularly preferably used. Examples of the alkyl acrylate having an alkyl group of 2 to 8 include ethyl acrylate, propyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate and the like, but butyl acrylate is particularly preferably used. As the crosslinkable monomer, for example, aromatic divinyl monomer such as divinylbenzene, alkane polyol polyacrylate or alkane polyol polymethacrylate such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol diacrylate, hexanediol diacrylate, and hexanediol dimethacrylate. Etc., but butylene glycol diacrylate and hexanediol diacrylate are particularly 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, and allyl methacrylate is particularly preferably used. Examples of the monomer constituting the glassy polymer include methyl methacrylate and a monomer copolymerizable with methyl methacrylate. As a monomer copolymerizable with methyl methacrylate, for example, ethyl acrylate, alkyl acrylate such as butyl acrylate, ethyl methacrylate, alkyl methacrylate such as butyl methacrylate, styrene, vinyltoluene, aromatic vinyl such as α-methylstyrene, aromatic vinylidene, Examples thereof include vinyl cyanide such as acrylonitrile and methacrylonitrile, and vinyl polymerizable monomers such as vinylidene cyanide. Particularly preferred are ethyl acrylate, styrene and acrylonitrile.

The core-shell polymer used in the present invention is preferably a core-shell polymer in which substantially no anion is detected. Specifically, emulsion polymerization is carried out using a nonionic surfactant and a polymerization initiator in which the radicals generated are neutral. The core-shell polymer obtained by the above is preferable. The anion content of the core-shell polymer is such that it cannot be detected by a usual anion qualitative test. For example, as a measuring method, 5 g of the sample (core-shell polymer) is weighed in a 50 ml Erlenmeyer flask, and ion-exchanged water 20
Add ml and stir with a magnetic stirrer for 3 hours.
Next, the filtrate filtered through No. 5C filter paper was divided into two parts, and 0.5 ml of a 1% barium chloride aqueous solution was added to one of the two parts, and the generation of turbidity was comparatively observed (a qualitative test for sulfate ion). Further, the same treatment was carried out, and 0.1N silver nitrate aqueous solution was added in place of 1% barium chloride, and the occurrence of turbidity was comparatively observed (a qualitative test for halogen ions). Other anions such as metal salts of carboxylic acids are similarly measured by the measuring method usually used as a qualitative test.

The preferable addition amount of the (B) impact resistance improver which can be used in the present invention is (A) polyacetal resin 100.
3 to 50 parts by weight, more preferably 5 to 5 parts by weight.
40 parts by weight. If it is less than 3 parts by weight, the effect of improving the impact resistance is poor, and if it exceeds 50 parts by weight, the mechanical properties, heat resistance, chemical resistance, etc. inherent to the polyacetal resin are greatly deteriorated, which is not preferable.

When the composition of the present invention, particularly thermoplastic polyurethane is used, it is preferable to add an isocyanate compound or an isothiocyanate compound for the purpose of further improving impact resistance, weld characteristics and the like. next,
The isocyanate compound and the isothiocyanate compound used in combination in the present invention are those containing two or more isocyanate groups or isothiocyanate groups in the molecule. Specifically, for example, toluene diisocyanate,
Toluene diisothiocyanate, xylene diisocyanate, xylene diisothiocyanate, diphenylmethane diisocyanate, diphenylmethane diisothiocyanate, phenylene diisocyanate, phenylene diisothiocyanate, naphthalene diisocyanate, naphthalene diisothiocyanate, ethylene diisocyanate, ethylene diisothiocyanate, propylene diisocyanate, propylene diisocyanate Isothiocyanate, tetramethylene diisocyanate, tetramethylene diisothiocyanate, hexamethylene diisocyanate, hexamethylene diisothiocyanate, cyclohexylene diisocyanate, cyclohexylene diisothiocyanate, dicyclohexylmethane diisocyanate, dicyclohexylmethane diisocyanate Sochioshianeto, isophorone diisocyanate, isophorone diisothiocyanate, etc.,
And dimers or trimers thereof. The blending amount of the isocyanate compound or isothiocyanate compound used here is preferably in the range of 0.01 to 10% by weight with respect to the component (A) + the component (B).

In the polyacetal resin composition of the present invention, a known antioxidant, a nitrogen compound, an alkali or alkaline earth metal compound or the like is added to enhance the thermal stability.
It is desirable to use one kind or a combination of two or more kinds. The resin composition of the present invention, in order to impart desired properties depending on its purpose, conventionally known additives such as lubricants, release agents, antistatic agents and other surfactants, or organic polymer materials other than the above, Inorganic or organic fibrous, granular,
It is also possible to add one or more plate-like fillers. The composition of the present invention can be easily prepared by a known method generally used as a conventional resin composition preparation method. For example, after mixing the components, kneading and extruding with an extruder to prepare pellets, followed by a method of molding, once preparing pellets having a different composition, mixing a predetermined amount of the pellets and subjecting to molding Any method such as a method of obtaining a molded article having a composition or a method of directly charging one or more of each component into a molding machine can be used.

[0014]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.
The methods used for evaluation in the examples are as follows. (1) Crystallization characteristics <Crystallization time> Differential scanning calorimeter D manufactured by Perkin Elmer
Using SC7 type, the sample amount was about 5 mg, and the sample was kept at 200 ° C. for 5 minutes and then cooled at 10 ° C. per minute. When the temperature reached 152 ° C., the temperature was kept constant and an endothermic and exothermic curve, so-called DSC curve, with respect to the elapsed time from the start of holding was recorded. The crystallization time was defined as the time from when the temperature reached 152 ° C to the appearance time of the recorded peak. (2) Impact characteristics Izod impact strength The resin pellets prepared in the examples and comparative examples were tested at a cylinder temperature of 190 ° C using an in-line injection molding machine (J75SA, manufactured by Japan Steel Works) with a mold clamping force of 75 tons. A sample (a rectangular parallelepiped having a width of 12.7 mm, a thickness of 6.4 mm and a length of 64 mm) was molded, a notch was formed according to the method of ASTM D 256, and an Izod impact value was measured. A higher Izod impact value is judged to be better. Drop weight impact strength Using the in-line injection molding machine (J150SA, manufactured by Japan Steel Works) with a mold clamping force of 150 tons, the resin pellets prepared in the examples and comparative examples were tested at a cylinder temperature of 190 ° C. , A flat plate with a width of 120.0 mm and a thickness of 2.0 mm) was molded. Using a General Research Dynatap 8250, a weight with a tip R of 10 mm (2.9 kg) is 4 m / s at a speed of 4 m / s, and the energy absorbed by the sample at this time is obtained from a load cell provided at the rear of the weight tip. It was calculated from the load. (3) Weld characteristics Using the in-line injection molding machine (J75SA, manufactured by Japan Steel Works) having a mold clamping force of 75 tons, the resin pellets prepared in Examples and Comparative Examples were subjected to ISO tensile test at a cylinder temperature of 190 ° C. A dumbbell-shaped sample (narrowest section cross section: width 10 mm, thickness 2 mm, distance between marked lines 50 mm) was molded so that a weld was generated at the center of the test piece by injecting resin from both ends of the test piece. Tensile tester (Tensilon UTM-I-2500
Using Orientec Co., Ltd., the tensile strength and the tensile elongation were measured according to ASTM D638. The tensile strength and tensile elongation at this time were made into weld strength and weld elongation, and these were combined and made into weld characteristics. Generally, it is important that the weld elongation is particularly large. Practically, the weld elongation is required to be at least 10%, and 20% or more is considered to be good.

(4) Flow characteristics The resin pellets prepared in the Examples and Comparative Examples were treated with an in-line injection molding machine (PS20E2ASE, manufactured by Nissei Plastic Industry Co., Ltd.) having a mold clamping force of 20 tons to have a width of 3.0 mm and a thickness. 0.3mm, length
Molding was performed using a mold having a 50 mm cavity (the gate was installed at one end of the width surface) under conditions of a cylinder temperature of 190 ° C, an injection speed of maximum, and an injection pressure of 750 kgf / cm ² . At this time, the flow length in the longitudinal direction was measured and defined as the flow characteristic. The longer the flow length, the better the flowability, but a flow length of at least 20 mm is required for use in general injection molding without problems.
Especially, if it is 15 mm or less, the usable range of application is greatly limited.

Example 1 Two cylinders having an inner diameter of 80 mm and a cross section in which two circles partially overlap each other, a barrel with a jacket for passing a heat (cold) medium on the outside, and a paddle for stirring and propelling inside the barrel Using a continuous type mixing reactor having a rotating shaft in the longitudinal direction, hot water of 80 ° C is passed through the jacket, and the two rotating shafts are rotated at a speed of 100 rpm,
Trioxane containing 5.5% by weight of 1,3-dioxolane as a comonomer was continuously supplied to one end of the solution, and at the same time, a solution of boron trifluoride butyl etherate dissolved in cyclohexane to a concentration of 1% was added. , Continuously added so that BF ₃ was 30 ppm to all monomers, copolymerization was performed, and the reaction mixture discharged from the other end was immediately added to an aqueous solution containing 0.1% triethylamine, and the mixture was heated at 80 ° C for 1 hour. The mixture was stirred, deliquored and dried at 135 ° C. for 2 hours to obtain an acetal copolymer. The comonomer content in the obtained acetal copolymer is 5.0% by weight,
The crystallization time was 10 minutes. To 100 parts by weight of the obtained acetal copolymer, 0.2 parts by weight of melamine as a heat stabilizer, 0.2 parts by weight of the antioxidant Irganox 1010 manufactured by Ciba-Geigy Co., Ltd., and a thermoplastic resin having a glass transition temperature of -17 ° C as an impact resistance improver 20 parts by weight of polyurethane and 1.2% by weight of isophorone diisocyanate trimer were added, and after blending, they were melt mixed with a twin-screw extruder to obtain a pelletized composition. The above evaluation was performed using the obtained pellets. The results are shown in Table 1. Comparative Example 1 A pelletized composition was obtained in the same manner as in Example 1 except that an acetal copolymer having a comonomer content of 2.0% by weight and a crystallization time of 1 minute was used, and then evaluated. The results are shown in Table 2.
Shown in. Examples 2 to 3 A pelletized composition was prepared in the same manner as in Example 1 except that the blending amount of the thermoplastic polyurethane of Example 1 was changed to 15 parts by weight (Example 2) or 30 parts by weight (Example 3). After obtaining, evaluation was performed. The results are shown in Table 1. Comparative Example 2 A pelletized composition was obtained in the same manner as in Example 2 except that the acetal copolymer of Example 2 was replaced with the acetal copolymer shown in Table 2, and then the composition was evaluated. The results are shown in Table 2. Examples 4-5 Acetal copolymers, thermoplastic polyurethane (15 parts by weight) and isophorone diisocyanate 3 shown in Table 1
The pelletized composition was obtained in the same manner as in Example 1 using the monomer (1.2% by weight), and then evaluated. The results are shown in Table 1. Examples 6 to 7 The acetal copolymer used in Example 1 was mixed with 20 (or 15) parts by weight of a core-shell polymer (PO-0135 manufactured by Takeda Pharmaceutical Co., Ltd.), and pelletized compositions were prepared in the same manner as in Example 1. After obtaining, evaluation was performed. The results are shown in Table 1. Comparative Example 3 A pelletized composition was obtained in the same manner as in Example 5 except that an acetal copolymer having a comonomer content of 2.0% by weight and a crystallization time of 1 minute was used, and then evaluated. The results are shown in Table 2.
Shown in.

[0017]

[Table 1]

[0018]

[Table 2]

Note-1) DO: 1,3-dioxolane EO: ethylene oxide BDFo: 1,4-butanediol formal Note-2) TPU: thermoplastic polyurethane CSP: core-shell polymer (Takeda Chemical Industries PO-0135
)

[0020]

As is apparent from the above description and the examples, according to the present invention, it is possible to obtain a very preferable resin composition in which the impact resistance of polyacetal is remarkably improved, and further the weld characteristics and the fluidity are improved. . The composition of the present invention is suitably used in a wide range of fields requiring impact resistance,
For example, automobile parts (clips, fasteners, rivets,
It is ideal for switches, etc., home appliances parts (various gears, panels, etc.).

Claims (6)

[Claims] 1. To 100 parts by weight of a polyacetal resin having a crystallization time of 5 minutes or more, (B) a thermoplastic polyurethane-based and / or core-shell polymer-based impact modifier is added.
A polyacetal resin composition containing about 50 parts by weight. 2. The polyacetal resin composition according to claim 1, wherein the glass transition temperature of the thermoplastic polyurethane is −15 ° C. or lower. 3. The polyacetal resin composition according to claim 1, wherein the soft component of the thermoplastic polyurethane is one or more selected from polyalkylene adipates and polyalkyl ethers. 4. The polyacetal resin composition according to claim 1, wherein the core-shell polymer is polymerized by a polymerization method in which anions are not substantially detected. 5. A polyacetal resin having (A) a crystallization time of 5 minutes or more contains 3 to 30% by weight of an oxyalkylene unit having 2 or more carbon atoms in a polymer having an oxymethylene unit as a main constituent unit. Claims 1-4 which are those
The polyacetal resin composition according to claim 1. 6. The monomer component constituting the oxyalkylene unit having 2 or more carbon atoms is ethylene oxide, 1,3
-Dioxolane, diethylene glycol formal and
The polyacetal resin composition according to claim 5, which is at least one kind of 1,4-butanediol formal.