JP2017222770A - Styrenic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a styrenic resin that has flowability, heat resistance, and mechanical strength in a balanced manner and also is less prone to adhere to a die, in the field of injection molding.SOLUTION: A styrenic resin is characterized in that: a melt mass flow rate (MFR) measured under the conditions of 200°C and 49 N load is 15-40 g/10 min, a methanol soluble content is 0.5-1.8 mass%, and the ratio between a weight average molecular weight (Mw) and a number average molecular weight (Mn) (Mw/Mn) is 1.8-2.6.SELECTED DRAWING: None

Description

  The present invention relates to a styrenic resin that has an excellent balance of fluidity, heat resistance, and mechanical strength, and has little mold adhesion.

  Styrenic resins are widely used for general goods, light electrical components, etc. due to their excellent moldability and practical strength. However, in recent years, in the field of injection molding applications, it has been required to shorten the time required for the so-called molding cycle of plasticization, injection, holding pressure and cooling of the resin composition and to increase the molding efficiency. In order to shorten the molding cycle, it is necessary to have high fluidity at the time of injection and to solidify at a high temperature at the time of cooling, in other words, to be difficult to soften at a high temperature, that is, to have excellent heat resistance. In addition, in an injection molded product, residual distortion formed during molding becomes a problem. That is, it is known that when the residual strain is large, the impact strength of the molded product is remarkably lowered. Therefore, it is necessary to maintain the residual strain as low as possible. Here, the residual strain is considered to be formed by flow shearing of the resin at the time of injection molding, and from the viewpoint of reducing the residual strain, it is necessary to have high fluidity at the time of injection molding.

As an attempt to meet this requirement, a method has been proposed in which the molecular weight of the resin is lowered and the fluidity of the resin composition is increased. However, this method has a problem in that the strength of the resin is reduced, and cracking occurs during the protruding step of the molded product or when the molded product is used. Further, as a method for improving fluidity without lowering the molecular weight of the resin, there is a method in which a plasticizer such as liquid paraffin is added to the resin. However, this method has a problem that the heat resistance of the resin is lowered by the plasticizer. In addition, there has been a problem that a low molecular weight substance adheres to a mold or a molded product during injection molding. Furthermore, Patent Document 1 describes a styrenic resin excellent in fluidity and heat resistance. However, since the molecular weight distribution is wide and many low molecular weight components are contained, it is difficult to achieve a sufficient level of mechanical strength. There's a problem.
JP2009-275185A

  The present invention provides a styrenic resin that is excellent in the balance of fluidity, heat resistance, and mechanical strength and that can provide a molded product with little adhesion to a mold.

In order to achieve the above-mentioned object, the present inventors have conducted extensive research. As a result, the melt mass flow rate (MFR), methanol-soluble matter, weight average molecular weight (Mw) and number average molecular weight (Mn) in the styrenic resin are described. It was found that the above-mentioned problem can be achieved by setting the ratio (Mw / Mn) in a specific range. The present invention is based on this finding and has the following gist.
(1) Melt mass flow rate (MFR) measured under the conditions of 200 ° C. and 49 N load is 15 to 40 g / 10 min, methanol soluble content is 0.5 to 1.8 mass%, and weight average molecular weight (Mw) And a number average molecular weight (Mn) ratio (Mw / Mn) of 1.8 to 2.6.
(2) The styrene resin according to (1), wherein the weight average molecular weight (Mw) is 100,000 to 170,000.
(3) The styrenic resin according to (1) or (2), wherein the Vicat softening temperature measured at a load of 50 N is 99 to 104 ° C.

  Since the styrenic resin of the present invention is excellent in fluidity and heat resistance, the molding cycle can be shortened, and the obtained molded product has low residual strain and excellent mechanical strength, and also has little mold adhesion, Appearance is also excellent.

  The present invention will be described in detail below.

  The styrenic resin of the present invention is obtained by radical polymerization of a styrenic monomer, and the polymerization method is a known method such as bulk polymerization method, bulk / suspension two-stage polymerization method, solution polymerization method. Etc. can be manufactured.

  As a styrene-type monomer, styrene, (alpha) -methylstyrene, o-methylstyrene, p-methylstyrene etc. are individual or a mixture, Especially preferably, it is styrene. In addition, monomers that can be copolymerized with these styrenic monomers, for example, monomers such as acrylonitrile, methacrylic acid esters, and acrylic acid esters, can be copolymerized as long as the effects of the present invention are not impaired. it can.

  The melt mass flow rate (MFR) measured under the conditions of 200 ° C. and 49 N load of the styrene resin of the present invention is 15 to 40 g / 10 minutes, preferably 15 to 34 g / 10 minutes, and more preferably 15 to 27 g. / 10 minutes. If it is less than 15 g / 10 minutes, the fluidity is insufficient, and shortening of the molding cycle cannot be expected, and if it exceeds 40 g / 10 minutes, the mechanical strength decreases. The melt mass flow rate under the conditions of 200 ° C. and 49 N load was measured based on JIS K-7210. The melt mass flow rate of the styrene-based resin is a parameter representing the fluidity at the time of melting, but can be adjusted by controlling the molecular weight and molecular weight distribution. In addition, various additive components such as styrene oligomer (styrene dimer, styrene trimer) and white oil that are by-produced in the polymerization process and devolatilization process, low molecular weight components such as residual styrene monomer and polymerization solvent are effective as plasticizers. Because of this, there is an effect of increasing the melt mass flow rate.

The methanol-soluble component of the styrene resin of the present invention is 0.5 to 1.8% by mass, preferably 0.5 to 1.6% by mass. If the methanol-soluble content exceeds 1.8% by mass, the heat resistance is lowered and the molding cycle cannot be shortened. Moreover, it is difficult to make it less than 0.5 mass%, and productivity falls remarkably. The methanol-soluble component refers to a component that is soluble in methanol in the resin composition. For example, in addition to styrene oligomers (styrene dimer, styrene trimer) that are by-produced in the polymerization process or devolatilization process of styrene resin, Various additive components such as oil, low molecular weight components such as residual styrene monomer and polymerization solvent are included. Methanol-soluble matter suppresses the amount of styrene oligomer (styrene dimer, styrene trimer) generated as a by-product in the polymerization process as much as possible, refrains from using various additives such as white oil, and suppresses the amount of residual styrene monomer and polymerization solvent Can be reduced.
The methanol-soluble component is precisely weighed (mass P) of 1 g of styrene-based resin, dissolved by adding methyl ethyl ketone, and 400 mL of methanol is rapidly added to precipitate and precipitate the methanol-insoluble component (resin component). After leaving still for about 10 minutes, it was gradually filtered through a glass filter to separate methanol-insoluble matter, dried in a vacuum dryer at 125 ° C. under reduced pressure for 2 hours, and then allowed to cool in a desiccator for about 30 minutes. By measuring the mass N of the dried methanol-insoluble matter, it was determined by the following formula.
Methanol-soluble content (mass%) = (P−N) / P × 100

The weight average molecular weight (Mw) of the styrene resin of the present invention is 100,000 to 170,000, preferably 120,000 to 160,000. If the Mw is less than 100,000, the mechanical strength is lowered, and if it exceeds 170,000, the fluidity is insufficient. Moreover, the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) is 1.8 to 2.6, preferably 2.0 to 2.4. When Mw / Mn exceeds 2.6, since many low molecular weight components are contained, the mechanical strength is lowered, and it is difficult to make it less than 1.8, and the productivity is significantly lowered.
The weight average molecular weight (Mw) and the number average molecular weight (Mn) in the present invention were measured under the following conditions using gel permeation chromatography (GPC).
GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer The molecular weight of the present invention is calculated as the molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

  The molecular weight of the styrene resin of the present invention can be adjusted by using a solvent or a chain transfer agent when radically polymerizing the styrene monomer. As the solvent, toluene, ethylbenzene, xylene and the like can be used. Although the usage-amount of a solvent is not specifically limited, Use of the range of 0 mass%-50 mass% with respect to 100 weight% of polymerization raw material solutions is preferable. As the chain transfer agent, n-dodecyl mercaptan, t-dodecyl mercaptan, α-methylstyrene dimer or the like is used, and α-methylstyrene dimer is preferable. The amount of the chain transfer agent used is preferably 0.01% by mass to 0.5% by mass and more preferably 0.03 to 0.3% by mass with respect to the styrenic monomer. The reaction temperature is preferably in the range of 80 to 200 ° C, more preferably 90 to 180 ° C. If the reaction temperature is lower than 80 ° C., the productivity is lowered, which is industrially unsuitable. On the other hand, if it exceeds 200 ° C., a large amount of low molecular weight components are generated, which is not preferable. When the target molecular weight cannot be adjusted only by the polymerization temperature, it may be controlled by the initiator amount, the solvent amount, the chain transfer agent amount, or the like. The reaction time is generally 0.5 to 20 hours, preferably 2 to 10 hours. When the reaction time is shorter than 0.5 hours, the reaction does not proceed sufficiently. On the other hand, when the reaction time is longer than 20 hours, the productivity is low and industrially unsuitable.

  The Vicat softening temperature of the styrene resin of the present invention measured at 50 N load is 99 to 104 ° C, preferably 100 to 104 ° C. When the Vicat softening temperature is less than 99 ° C., the heat resistance is insufficient, and it is difficult to solidify at a high temperature during cooling, and a shortening of the molding cycle cannot be expected. In addition, 104 ° C. is a structural limit in radical polymerization polystyrene. The Vicat softening temperature was determined according to JIS K-7206 at a heating rate of 50 ° C / hr and a test load of 50N.

  If necessary, the styrenic resin of the present invention may use metal soaps such as zinc stearate, calcium stearate, magnesium stearate, stearic acid, ethylene bisstearyl amide, etc. as an internal lubricant or an external lubricant. it can. Moreover, although plasticizer components, such as white oil, can also be added, heat resistance falls. In addition, an antioxidant may be added to suppress thermal deterioration during the molding process.

  The molding method of the styrenic resin of the present invention is not particularly limited, but known molding methods such as extrusion molding, injection molding, injection hollow molding, and foam molding can be applied, and molding methods combined with various molding techniques may be used. Furthermore, although a method of forming into a sheet or film using a T-die sheet extruder, a biaxial stretching apparatus, or an inflation processing apparatus can be applied, injection molding is suitable as a method for obtaining a molded product, and the molding thus obtained The product can be used for food containers (cups), CD cases, miscellaneous goods and the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.

(Method for producing styrene resins PS-1 to PS-9)
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor. A raw material solution was prepared with the raw material composition described in Table 1, and the raw material solution was continuously supplied to the first reactor at a flow rate described in Table 1. The polymerization initiator and the chain transfer agent were added to and mixed with the raw material solution so that the addition concentration (concentration based on mass relative to the raw material styrene) shown in Table 1 was reached at the inlet of the first reactor. The chain transfer agents listed in Table 1 are as follows.
Polymerization initiator: t-butyl cumyl peroxide (Perbutyl C manufactured by NOF Corporation)
Chain transfer agent-1: α-methylstyrene dimer (NOFMER MSD manufactured by NOF Corporation)
Chain transfer agent-2: t-dodecyl mercaptan In addition, in the 3rd reactor, the temperature gradient was made along the direction of flow, and it adjusted so that it might become the temperature of Table 1 in an intermediate part and an exit part.
Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted by two stages in series, and the preheater was adjusted to the resin temperature shown in Table 1. By adjusting the temperature and adjusting to the pressure shown in Table 1, unreacted styrene and ethylbenzene are separated and then extruded into a strand form from a perforated die, and the strand is cooled and cut by a cold cut method. Pelletized. In addition, PS-1-6 was used for the Example, PS-7-9 was used for the comparative example, and the physical-property measurement was performed on the following conditions. The results are shown in Table 2.

(1) Falling ball impact strength (mechanical strength)
A test piece of 160 × 160 × 3 mm thickness was prepared using an injection molding machine, and the test was carried out according to JIS K-7221 except that the weight of the sphere was 16.6 g, and the value of 50% fracture height was measured. did.
(2) Formability When a box-shaped container having a thickness of 1 mm was formed at 210 ° C. using an injection molding machine, evaluation was performed according to the following evaluation criteria.
○: Can be molded without problems.
Short: Short shot.
Burr: Burr occurs.
(3) Mold adhesion When a test piece was prepared at 210 ° C. using an injection molding machine, it was evaluated according to the following evaluation criteria.
○: There is no adhesion to the mold after 100 shots of continuous molding.
X: There is adhesion to the mold after 100 shots of continuous molding.

  By using the styrenic resin of the example, it is possible to obtain a molded product having an excellent balance of fluidity, heat resistance, and mechanical strength and having little adhesion to the mold.

  In Comparative Example 1, the moldability deteriorated because the MFR was too low.

  In Comparative Example 2, since the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) was too large, the mechanical strength was lowered.

  In Comparative Example 3, since there was too much methanol-soluble matter, moldability and mold adhesion deteriorated.

  From the above results, only when the melt mass flow rate (MFR), methanol-soluble content of the styrene resin, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw / Mn) is in a specific range. It was found that the fluidity, heat resistance and mechanical strength were excellent, and the appearance was excellent with little adhesion to the mold.

  The styrenic resin of the present invention has an excellent balance between fluidity and heat resistance, can shorten the molding cycle, has low residual strain, has excellent mechanical strength, and has excellent appearance with little mold adhesion. It can be suitably used for application fields.

Claims (3)

  Melt mass flow rate (MFR) measured under the conditions of 200 ° C. and 49 N load is 15 to 40 g / 10 min, methanol soluble content is 0.5 to 1.8 mass%, and weight average molecular weight (Mw) and number average Styrenic resin characterized by having a molecular weight (Mn) ratio (Mw / Mn) of 1.8 to 2.6.   The styrene resin according to claim 1, wherein the weight average molecular weight (Mw) is 100,000 to 170,000.   The styrenic resin according to claim 1 or 2, wherein the Vicat softening temperature measured at a load of 50 N is 99 to 104 ° C.