JP3000845B2 - Foam comprising polystyrene resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam comprising a polystyrene resin composition. More specifically, the present invention provides a foam having high melt tension and excellent fluidity, so that there is little outgassing during foam molding, a high expansion ratio is obtained, the foam cells are uniform, and the appearance is good. And a foam comprising a polystyrene-based resin composition having excellent processing productivity and excellent impact strength.

[0002]

2. Description of the Related Art It is widely used to form a foam by foaming polystyrene. However,
Polystyrene has a problem that the melt tension is low, accompanied by outgassing during foaming processing, so that it is difficult to obtain a high expansion ratio, the foam cells become uneven, the appearance is poor, and the impact strength of the obtained foam is low. ing. By the way, there is known a method of increasing the melt tension and impact strength by increasing the molecular weight of polystyrene. However, according to this method, there is a problem that the fluidity is reduced and the productivity during foam molding is reduced.

[0003]

In such a situation,
The problem to be solved by the present invention is that, since it has high melt tension and excellent fluidity, there is little outgassing during foam molding, a high expansion ratio is obtained, the foam cells are uniform, and the appearance is good. An object of the present invention is to provide a foam made of a polystyrene-based resin composition that can obtain a foam, has excellent processing productivity, and has excellent impact strength.

[0004]

That is, the present invention provides a polystyrene resin composition containing, as a polymer component, 50 to 100% by weight of a polystyrene copolymer satisfying the following conditions (A) to (F). The present invention relates to a foam comprising: (A): A compound having a plurality of vinyl groups is 100 to 10
(B): The weight average molecular weight is 200,000 to 2,000,000 (C): In the molecular weight distribution, the ratio of 100,000 or less is 20 to 30% by weight, and the molecular weight is 1,000,000 or more. (D): the number of branch points in the Z average molecular weight is 1 to 20 (E): the insoluble matter in the methyl ethyl ketone / methanol mixed solvent is 3% by weight or less ( F): Methanol soluble content is 5% by weight or less

[0005] The polystyrene copolymer of the present invention contains a styrene compound and a compound having a plurality of vinyl groups as constituent monomer.

[0006] As styrene compounds, styrene, α
Α-substituted alkylstyrene such as -methylstyrene, p
Nucleus-substituted alkylstyrenes such as -methylstyrene;

Compounds having a plurality of vinyl groups include:
Examples thereof include divinylbenzene and ethylene glycol dimethacrylate. The content of the compound having a plurality of vinyl groups is 100 to 1000 ppm by weight, preferably 100 to 700 ppm by weight. If the content is too small, it is difficult to obtain the number of branch points in the Z-average molecular weight of the present invention, while if the content is too large, it is difficult to obtain the methyl ethyl ketone / methanol mixed solvent insolubles of the present invention.

In the polystyrene copolymer of the present invention, in addition to the styrene compound and the compound having a plurality of vinyl groups, a compound copolymerizable with the styrene compound, for example, acrylonitrile, methacrylonitrile, methacryl Acid, vinyl monomers such as ester derivatives such as methyl methacrylate, furthermore, maleic anhydride,
It may contain maleimide, nucleus-substituted maleimide and the like.

The polystyrene copolymer of the present invention has a weight average molecular weight of 200,000 to 2,000,000, preferably 200,000 to 1,000,000.
Million, more preferably 300,000 to 1,000,000. If the molecular weight is too small, the melt tension and impact strength are poor. On the other hand, when the molecular weight is excessive, the fluidity is poor.

In the polystyrene copolymer of the present invention, the proportion of a molecular weight of 100,000 or less in the molecular weight distribution is 20 to 30% by weight, and the proportion of a molecular weight of 1,000,000 or more is 1 to 30% by weight, preferably 5 to 20% by weight. belongs to. Molecular weight 1
If the ratio is less than 100,000, the fluidity is poor, while if the ratio is too high, the melt tension is poor and the appearance of the foam is poor. On the other hand, when the ratio of the molecular weight of 1,000,000 or more is too small, the melt tension is poor, and the appearance of the molded article is poor. On the other hand, if the ratio is excessive, the fluidity is poor.

The polystyrene copolymer of the present invention has a number of branch points of 1 to 20, preferably 2 in the Z average molecular weight.
~ 15. When the number of the branch points is too small, the fluidity is poor. On the other hand, when the number of the branch points is too large, the fluidity is poor and the appearance of the molded article is poor. Here, the number of branch points in the Z-average molecular weight refers to the number of branch points included in a molecular chain representing a high molecular weight component considered to reduce the fluidity of a polystyrene resin composition having a certain molecular weight distribution. This is a corresponding concept and is required in the following method.
That is, the number of branch points in the weight average molecular weight and the Z average molecular weight is determined by a viscosity-GPC method using gel permeation chromatography (GPC) equipped with a differential refractometer and a viscometer as a detector. For details, see The Rubber Association of Japan, Vol. 45, No. 2,
It is described on pages 105-118 (1972). The number of branch points (Bn (M)) at the molecular weight M is determined by the following equation.

[IV (M) / IV _L (M)] ^2/3 =
[(1 + Bn (M) / 7) ^1/2 + 4/9 · Bn (M)]
^-1/2 where IV (M) and IV _L (M) are viscosity-GP
It is the intrinsic viscosity at the molecular weight M of the linear polystyrene as the sample and the standard sample measured by the method C.

The polystyrene-based copolymer of the present invention has a methyl ethyl ketone / methanol mixed solvent insoluble content of 5% by weight or less, preferably 3% by weight or less. If the insoluble content is excessive, the fluidity is inferior, and if molded, the appearance of the foamed product is inferior. The insoluble matter in the methyl ethyl ketone / methanol mixed solvent is measured by the following method. That is, 0.5 g of the resin composition was mixed with a mixed solvent of methyl ethyl ketone / methanol (10/1 volume mixing ratio).
Dissolve in 0 ml with stirring at room temperature for 2 hours. This solution is filtered, and the insoluble matter separated by the filter paper is dried and precisely weighed. The weight ratio of the resin composition component obtained by such an operation to the initially used resin composition is defined as the insoluble content.

The polystyrene copolymer of the present invention has a methanol-soluble content of 3% by weight or less, preferably 2% by weight.
These are: When the amount of the soluble component is excessive, the melt tension is poor, and the appearance and the expansion ratio are poor. The methanol-soluble matter is measured by the following method. That is, about 1 g of the resin composition
Is dissolved in 10 ml of methyl ethyl ketone at room temperature,
Reprecipitate by adding 300 ml of methanol, collect the solids by filtration, dry and weigh accurately. The weight ratio of the resin composition component reduced by the above operation to the initially used resin composition is defined as a methanol-soluble component.

As a polymerization method for the polystyrene copolymer of the present invention, a batch suspension polymerization method or a continuous bulk polymerization method can be used. Either a thermal polymerization method or a polymerization method using an initiator can be used, and various radical polymerization initiators can be used as the polymerization initiator. As the polymerization tank, a complete mixing type stirring polymerization tank, a plug flow type full (vertical or horizontal) polymerization tank, a static mixing tube type polymerization tank, or a combination of these polymerization tanks can be used.

The polystyrene-based copolymer of the present invention can be optimally produced by the following method in producing a continuous bulk polymerization process. That is, when polymerizing a compound having a plurality of vinyl groups and a styrene compound or a compound having a plurality of vinyl groups, a styrene compound and a compound copolymerizable with the styrene compound, a styrene compound and a styrene compound are used. 100 to 1000 ppm by weight, preferably 100 to 70
0 ppm by weight of a compound having a plurality of vinyl groups is uniformly mixed in advance, and the mixture is continuously supplied to a polymerization tank. At a polymerization temperature of 140 to 200 ° C., the final conversion is 60% by weight or more, preferably The polymerization mixture is polymerized to 70% by weight or more, and the polymerization mixture is heated at 200 to 280 ° C.
Lead to a preheater at 20-270 ° C, then 200-280
C., preferably at 220-270 ° C., through a vacuum degassing tank,
The unreacted monomer is recovered to obtain a target polystyrene copolymer.

If the amount of the compound containing a plurality of vinyl groups is too small, it is difficult to obtain the degree of branching in the Z-average molecular weight of the present invention, so that the balance between fluidity and melt tension is lacking. On the other hand, if the amount of the compound is too large, it is difficult to obtain an insoluble portion of the methyl ethyl ketone / methanol mixed solvent of the present invention, so that the fluidity is poor. In addition, when partially polymerizing only the styrene-based compound first and then adding and polymerizing a compound containing a plurality of vinyl groups, only the compound containing a plurality of vinyl groups was highly polymerized. A three-dimensional crosslinked portion is generated, and the amount of insolubles in the methyl ethyl ketone / methanol mixed solvent becomes excessive. Further, when the polymerization is terminated while the above conversion is insufficient, unreacted vinyl groups remain in the polymer, a sufficient branched structure cannot be obtained, and the obtained resin composition has fluidity. May be inferior.

The polymerization must be carried out in a temperature range from 140 to 200 ° C. If the polymerization temperature is too low, a gel is generated, and the amount of the insoluble matter in the methyl ethyl ketone / methanol mixed solvent becomes excessive, which causes a trouble that the polymerization tank and piping are blocked. On the other hand, when the polymerization temperature is too high, the melt tension of the obtained copolymer becomes insufficient.

The polystyrene resin composition of the present invention comprises 50 parts of the above polystyrene copolymer as a polymer component.
To 100% by weight, preferably 60 to 100% by weight. If the content is too small, the above object of the present invention cannot be sufficiently achieved. In addition, as a polymer component other than the polystyrene-based copolymer of the present invention in the polystyrene-based resin composition, a styrene content of 10 to 90 w
It is preferred to use t%, preferably 20-80 wt% styrene-butadiene copolymer or styrene-grafted polybutadiene.

The polystyrene resin composition of the present invention comprises:
It can be obtained by adding a lubricant, an antistatic agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, a pigment, a dye, and the like, if necessary, in addition to the polymer component. Further, a plasticizer such as mineral oil, a polystyrene-based resin composition other than the present invention, and a recycled polystyrene-based resin may be used as long as the effects of the present invention are not impaired.

The method of foaming the polystyrene resin composition of the present invention to form a foam is not particularly limited. For example, a decomposable foaming agent and a polystyrene resin composition are melt-kneaded by an extruder and foamed. Method: A method in which a polystyrene resin composition is melted by an extruder, and an evaporating foaming agent is directly press-fitted from the middle of a cylinder, and kneaded and foamed; Small pellets or beads made of the polystyrene resin composition are extruded or suspended in an aqueous solution. A method of impregnating an evaporating foaming agent in a liquid and foaming the impregnated pellets or beads with steam.

Examples of the decomposition type foaming agent include azodicarbonamide, trihydrazinotriazine, benzenesulfonyl semicarbazide and the like. Examples of the evaporative foaming agent include propane, n-butane, i-butane, n-pentane, i-pentane, hexane, heptane, freon and the like.

The foam of the present invention can be prepared by vacuum forming and air forming methods due to its excellent melt tension and fluidity balance.
It is suitably used for molding packaging containers and the like, and has excellent processing productivity. In addition, due to its excellent foam uniformity and impact strength, it is optimally used as a cushioning packaging material, a heat insulating material, and a civil engineering material.

[0024]

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.

(1) MI (fluidity): JIS K721
0 was performed. In addition, temperature 200 ° C, load 5k
gf. (2) Melt tension (melt tension): Using a melt tension tester type II manufactured by Toyo Seiki Seisakusho, resin temperature 200 ° C., extrusion speed 20 mm / min, winding speed 13c
It was measured at m / sec. (3) Content of compound having a plurality of vinyl groups: Determined by pyrolysis gas chromatography. The thermal decomposition conditions were as follows: 0.5 mg of the sample was 600 ° C. for 10 seconds.

(4) Outgassing: The degree of outgassing during foam molding was evaluated by the expansion ratio. That is, G = (expansion ratio-1) × 100 / 1.05, and when G ≧ 200, it was represented by ○ (good), and when G <200, it was represented by x (poor). (5) Foaming ratio: expressed as 1.05 / sheet density. (6) Appearance and uniformity of foam cells: The appearance of the obtained foam was visually observed, and the results were as follows: ○ (there was no roughening of the sheet due to outgassing and the cells were uniform) and × (there was roughening of the sheet and the cells were rough. (Non-uniform). (7) Impact strength (falling ball impact): 5
Cut out to 0 mm x 50 mm and carried out in accordance with JIS K7211 except that the weight of the sphere was 28.8 g.
The value of the breaking height was measured.

Example 1 Divinylbenzene (purity: 55% by weight, manufactured by Tokyo Chemical Industry Co., Ltd.), which is a compound containing a plurality of vinyl groups, was added to a solution of 90% by weight of styrene and 10% by weight of ethylbenzene by adding 250% by weight to styrene. The resulting solution was continuously supplied to a continuous bulk polymerization reactor, and polymerized at 150 ° C. until the final addition rate reached 80 wt%.
The unreacted monomer was recovered through a vacuum deaeration tank at a temperature of ℃ C to obtain a polystyrene-based copolymer. Next, a decomposition temperature of 165 ° C. was added to 100 parts by weight of the polystyrene copolymer.
Azodicarbonamide-based blowing agent (gas generation = 180
ml / g: cell microphone 172-C manufactured by Sankyo Chemical Co., Ltd.)
1 part by weight, 90 mm with a 1200 mm T die
It was extruded and foamed with a mmφ extruder at a cylinder temperature of 160 ° C., a die temperature of 170 ° C. and a screw rotation speed of 40 rpm to obtain a uniform foamed sheet having a sheet thickness of 5.3 mm and a density of 0.29.

Comparative Example 1 Example 1 was repeated except that divinylbenzene was not used.
The sheet thickness was 4.0 mm and the density was 0.40.
g / cc foam sheet was obtained. Comparative Example 2 Divinylbenzene was not used and the polymerization temperature was 1
Except that the temperature was 30 ° C., the same procedure as in Example 1 was performed to obtain a foamed sheet having a sheet thickness of 5.0 mm and a density of 0.3 g / cc. Comparative Example 3 A sheet thickness of 3.5 mm and a density of 0.45 g / c were performed in the same manner as in Comparative Example 2 except that 3% of mineral oil was added.
Thus, a foamed sheet c was obtained. Table 1 shows the evaluation results.

The following can be understood from the results. Example 1, which satisfies the conditions of the present invention, shows excellent results in all evaluation items. On the other hand, Comparative Example 1 using a polystyrene-based resin composition having no branch point in the Z-average molecular weight and containing no compound having a plurality of vinyl groups has a low melt tension, has a high outgassing, and cannot be highly foamed. ,
Poor appearance and poor impact strength. Comparative Example 2 in which the molecular weight of Comparative Example 1 was increased and the melt tension was increased was inferior in fluidity, high in extrusion pressure and inferior in productivity. Comparative Example 3, which has no branch point in the Z-average molecular weight, does not contain a compound having a plurality of vinyl groups, and has an excessive amount of methanol-soluble components, is inferior in melt tension, outgassed severely, and inferior in appearance.

[0030]

[Table 1] -------------------- Content wt ppm * 1 300 0 0 0 Weight average molecular weight 10 ⁴ 35 25 35 35 Ratio of molecular weight of 100,000 or less wt% 24 27 22 22 Ratio of molecular weight of 1,000,000 or more wt% 9 0.6 4 4 Number of branch points * 2 4 0 0 0 MEK / MeOH insolubles wt% * 3 0 0 0 0 MeOH solubles wt% * 4 0.9 1.2 1.0 4.0 MI (g / 10min) 3.0 3.0 1.4 3.0 Melt tension (g) 24 10 19 9 Evaluation Extrusion Resin pressure kg / cm ² 91 89 150 90 Outgassing ○ × ○ × Expansion ratio (times) 3.6 2.6 3.5 2.3 Appearance ○ × ○ × Uniformity of foam cells ○ × × × Impact strength cm 50 30 50 40 −−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

* 1 DVB content: content of divinylbenzene * 2 Number of branch points: number of branch points in Z average molecular weight * 3 MEK / MeOH insoluble matter: methyl ethyl ketone /
Methanol mixed solvent insolubles * 4 MeOH solubles: methanol solubles

[0032]

As described above, the present invention has high melt tension and excellent fluidity, so that there is little outgassing during foam molding, a high expansion ratio is obtained, the foam cells are uniform, and the appearance is improved. Good foam can be obtained,
A foam made of a polystyrene resin composition having excellent processing productivity and excellent impact strength could be provided.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI C08L 51:04 (58) Investigated field (Int.Cl. ⁷ , DB name) C08J 9/04

Claims (4)

(57) [Claims] 1. The polymer component (A)
50 polystyrene copolymers satisfying the condition (F)
A foam comprising a polystyrene resin composition containing about 100% by weight. (A): A compound having a plurality of vinyl groups is 100 to 10
(B): The weight average molecular weight is 200,000 to 2,000,000 (C): In the molecular weight distribution, the ratio of 100,000 or less is 20 to 30% by weight, and the molecular weight is 1,000,000 or more. (D): the number of branch points in the Z average molecular weight is 1 to 20 (E): the insoluble matter in the methyl ethyl ketone / methanol mixed solvent is 3% by weight or less ( F): Methanol soluble content is 5% by weight or less (B) a weight average molecular weight of 200,000 to 100
The foam according to claim 1, wherein the number is 10,000. 3. The foam according to claim 1, wherein (D) the number of branch points in the Z average molecular weight is 2 to 15. 4. The foam according to claim 1, wherein the polymer component other than the polystyrene-based copolymer is a styrene-butadiene copolymer or a styrene-grafted polybutadiene.