JPH04236247A - Foam of high-strength styrenic resin having excellent secondary foaming moldability - Google Patents

Abstract

PURPOSE:To obtain high-strength styrenic resin foam moldable at low temperature, having excellent secondary foaming moldability by blending a specific styrenic polymer with a block copolymer in a fixed ratio and molding the prepared styrenic resin. CONSTITUTION:A styrenic resin comprising (A) a styrenic polymer composed of (i) 75-99.5wt.% constituent unit shown by formula I (R1 is H or methyl; R2 is H or 1-5C alkyl) and (ii) 0.5-25 wt.% constituent unit shown by formula II (R3 is H or methyl; R4 is 1-8C alkyl) and (B) a styrenic polymer composed of (iii) a vinyl aromatic hydrocarbon polymer made of a vinyl aromatic hydrocarbon such as styrene and (iv) a polymer block consisting essentially of a conjugated diene in a weight ratio of 40:60-95:5 in a ratio of the component A and B of 99.5:0.5-85:15 by weight is extrusion-molded to give the objective foam.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a styrenic resin foam which has excellent secondary foaming moldability and excellent strength of foam molded products. More specifically, the present invention relates to a block having a styrenic polymer composed of a styrene structural unit and an acrylic ester (methacrylic ester) structural unit, an aromatic hydrocarbon polymer block, and a polymer block mainly composed of a conjugated diene. The present invention relates to a styrenic resin foam made by foaming a styrene resin made of a copolymer, which has a specific thickness and density, has excellent secondary foaming moldability, and has excellent strength of the molded product.

0002

[Prior Art] Polystyrene resin foam can be secondary-foamed by heating and easily molded into a desired shape, and the resulting molded product is lightweight, has excellent mechanical strength, has a beautiful appearance, and is hydrophobic. Because it is highly flexible and has excellent insulation properties, it is used in food packaging materials and simple containers such as boxes, trays, and cups. Recently, from the viewpoints of improving productivity during secondary molding, reducing the molding defect rate, and improving deep drawability, styrenic resin foams that have good secondary foam moldability and can be molded at the lowest possible temperature have been desired. It is rare.

[0003] In addition, for food packaging trays, etc., in order to prevent cracks etc. from occurring during automatic packaging, it is necessary to improve the strength of foam molded products.
In order to make products thinner, there is a need to improve the strength of molded products. In the production of a series of heated secondary foamed products in which sheet-shaped polystyrene foam is heat-treated in a heating furnace to foam, then taken out of the heating furnace and molded in a mold, the temperature inside the heating furnace is constant. Due to uniformity and fluctuations in the temperature inside the furnace due to outside air temperature, part or all of the sheet may be underheated, resulting in the sheet being torn during molding, poor moldability, or conversely overheating. As a result, phenomena such as keloid formation on the surface of the molded product and variations in the thickness of the molded product occur.

[0004] In order to prevent the formation of keloids, there are known methods such as increasing the molecular weight of the styrene foam base material, pasting a film on the sheet surface, and forming a layer with high resin density, a so-called skin layer. However, with this method, it is difficult to obtain a foam with good shapeability, and in the case of a deep-drawn product, sheet tearing is likely to occur. In addition, in order to obtain a well-defined foam, a method is known in which plasticizers, lubricants, etc. are added to the styrene foam base material, but this method causes keloid-like defects that occur during overheating during secondary molding. phenomenon is likely to occur.

[0005] As a method for suppressing the formation of keloids and obtaining a styrene foam with good shapeability, it has been shown in Japanese Patent Application Laid-Open No. 62-22834 that it is effective to use a styrene resin foam with a wide molecular weight distribution. It is stated in the No. However, such molded products of polystyrene resin foams having a wide molecular weight distribution inherently have a drawback of low strength.

[0006] In addition, molding at low temperatures is desired to increase the productivity of molded products, but because conventional styrene resins have a high heat resistance of 105°C to 108°C, there is a limit to lowering the molding temperature. was there. Although it is possible to lower the heat resistance by adding a plasticizer, good molded products cannot be obtained for the reasons mentioned above. As described above, there is currently no foam that satisfies all market demands.

[0007]

[Means for Solving the Problems] In view of the current situation, the present inventors have developed a styrene polymer and an aromatic hydrocarbon polymer block consisting of a styrene monomer and an acrylic ester (methacrylic ester) monomer. The styrenic resin is made of a block copolymer with a polymer block mainly composed of conjugated diene and conjugated diene. The present invention was achieved through extensive research to develop a styrene resin foam that has excellent strength and can be molded at low temperatures.

That is, the present invention provides the following general formula (A);

[Chemical formula 3]

The following general formula (B);

[C4]

It consists of the structural unit shown as
The ratio of A) and (B) is in the range of (A): 75 to 99.5% by weight (B): 0.5 to 25% by weight (however, (A) + (B) = 100% by weight) It has a styrenic polymer (I), at least one vinyl aromatic hydrocarbon polymer block, and at least one polymer block mainly composed of a conjugated diene, and the weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 40:60-95
:5, the weight ratio of the styrene polymer (I) to the block copolymer (II) is 99.5:0.5 to 85:15. The object of the present invention is to provide a styrene resin foam having excellent secondary foaming moldability and strength, which is formed by molding a styrene resin. In addition, the thickness of the styrene resin foam is 0.1 mm to 10 mm, and the density is 0.03 to 0.5 g/
The present invention also provides a styrenic resin foam which is excellent in secondary foaming moldability in the form of a CC sheet and in the strength of a foamed molded product. The present invention will be explained in detail below.

[0011] The amount of structural unit (B) is 0.5 to 25% by weight.
is within the range of (The amount of structural unit (A) is 100-(B)
It is. ) More preferably, it is in the range of 2 to 20% by weight. If it exceeds 25% by weight, the heat resistance will decrease,
The practical range of secondary foam molded products becomes extremely narrow. Also, 0.
If it is less than 5% by weight, the effects of the present invention will not be achieved, and a foam molded article with good secondary foam moldability and excellent strength will not be obtained.

The degree of polymerization of the styrenic polymer (I) of the present invention is not particularly limited, but the degree of polymerization at 25° C. is 10% by weight, taking into account the shape of the secondary foam molded product, the purpose of use, etc.
The viscosity of the toluene solution is set in the range of 20 to 80 centivoise, more preferably in the range of 25 to 70 centivoise. If the viscosity of the 10% by weight toluene solution is less than 20 centivoise, the improvement in strength will be small. In addition, if the viscosity exceeds 80 centivoise, this is not preferable because it causes a decrease in productivity and an increase in power consumption when extruding the styrene resin to obtain a styrenic resin foam.

In the present invention, examples of the structural unit (A) include those having the following structure.

[0014]

[C5]

In the present invention, examples of the structural unit (B) include those having the following structure.

[0016]

[C6]

In the present invention, a block copolymer having at least one vinyl aromatic hydrocarbon polymer block and at least one, preferably two or more conjugated diene-based polymer blocks is used. use. Here, the polymer block mainly composed of conjugated diene means that the content of conjugated diene is 50% by weight or more, preferably 70% by weight.
Above, the polymer block is more preferably 90% by weight or more. The vinyl aromatic hydrocarbon copolymerized in the polymer block mainly composed of conjugated diene may be uniformly distributed in the polymer block or may be distributed in a tapered shape. The weight ratio of vinyl aromatic hydrocarbon to conjugated diene in the block copolymer is from 40:60 to 95:5, preferably from 50:50 to 90:10. When the content of the vinyl aromatic hydrocarbon is less than 40% by weight, the compatibility with the styrene polymer decreases, the appearance of the foamed molded product deteriorates, and the strength of the foamed molded product becomes brittle. If the amount exceeds 95% by weight, the strength of the foam and the molded product made from the foam will not be improved significantly.

The weight of the vinyl aromatic hydrocarbon polymer block in the block copolymer can be determined by a method of oxidizing the copolymer with di-t-butyl hydroperoxide using osmium tetroxide as a catalyst (for example, L.M. KOLTHOF
F, et al. , J. Polym. Sci. ,14
29 (1946)).

The block copolymer used in the present invention is a linear block copolymer (A-B) represented by the general structural formula below.
n...■ (A is a vinyl aromatic hydrocarbon polymer block, A(B-A)n...■ B is a polymer block mainly composed of a conjugated diene. B(A-B)n... ...■ The boundary between the A block and the B block does not necessarily have to be clearly distinguished.) Alternatively, it is a radial block copolymer represented by the following general formula.

[0020]

[Math 1]

In the general formulas (1) to (2), n is 1 to 4, and m is 1 to 3. In the block copolymer used in the present invention, the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is 10,000 to 70,000, preferably 15,000 to 60,000. The number average molecular weight of the polymer block mainly composed of conjugated diene is
There is no particular limit, but it is 500 to 200,000, preferably 1,000 to 100,000.

[0022] In order to produce the styrenic polymer for obtaining the styrenic resin foam of the present invention, methods known in the art for producing styrenic resins, such as bulk polymerization and solution polymerization, are used. Moreover, at this time, it is also possible to use a polymerization initiator commonly used in the production of styrenic polymers. In addition, styrenic polymers with a uniform composition can be produced using a complete mixing reactor, which is often used in copolymer manufacturing methods, or
A styrenic polymer having a non-uniform composition may be produced using a tubular reactor or a polymerization apparatus that is a combination of a complete mixing reactor and a tubular reactor. However, styrenic polymers with non-uniform composition that cause phase separation during extrusion, molding, etc. are not preferred. At this time, it is necessary to control the composition to a degree of non-uniformity that does not cause phase separation by using a method of adding additional raw materials, which is commonly used in the production of styrenic polymers.

Styrene is preferably used as the styrenic monomer used to obtain the styrenic polymer which is the base material of the present invention. Acrylic ester (methacrylic ester) monomers include butyl acrylate,
Butyl methacrylate etc. can be used. These monomers can be used alone or in combination. The block copolymer used in the present invention can basically be produced by conventionally known methods, such as Japanese Patent Publication No. 36-19286, Japanese Patent Publication No. 43-14979, Japanese Patent Publication No. 48-2423, Japanese Patent Publication No. 48 -4106 Publication, Special Publication No. 49-3695
Examples include the method described in Publication No. 7 and the like.

In the present invention, styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, pt-butylstyrene, etc. can be used as the vinyl aromatic hydrocarbon. These may be used alone or in combination of two or more. A particularly common one is styrene. The conjugated diene is a diolefin having a pair of conjugated double bonds, such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1, 3-butadiene, 1,3-
Pentadiene, 1,3-hexadiene, etc. can be used. These may be used alone or in combination of two or more. Particularly common ones include 1,3-butadiene and isoprene.

The styrenic resin which is the base material of the present invention can be obtained by blending the styrenic polymer (I) and the block copolymer (II). Styrenic polymer (I
) and block copolymer (II) weight ratio is 99.5:0
．． It is in the range of 5 to 85:15. More preferably 99:
The ratio is 1 to 90:10. The weight ratio of styrenic polymer is 9
If it exceeds 9.5% by weight, the strength reinforcing effect of the block copolymer will be small, which is not preferable. If the amount is less than 85% by weight, the blowing agent will greatly dissipate during curing of the foam, and the thickness of the molded product will fluctuate during secondary foam molding, making stable molding difficult. Furthermore, since the block copolymer is expensive, it increases the cost of the styrenic resin foam, which is undesirable.

The styrenic polymer (I) and the block copolymer (II) can be mixed by a known method, for example, by mixing using an extruder, a Banbury mixer, etc., or by feeding the two polymers into an extruder. A method such as melt-kneading is used at the stage of obtaining a styrene resin foam. Styrenic resin foam is produced by impregnating styrene resin with blowing agents such as lower hydrocarbons such as propane, butane, pentane, and hexane, and halogenated hydrocarbons such as methyl chloride, dichloromethane, trichloromonofluoromethane, and dichlorodifluoromethane. After supplying the styrene resin to the extruder, press the foaming agent into the extruder, melt and knead the foaming agent and styrene resin in the extruder, and then press the foaming agent into the extruder. By a known method such as extrusion from a die etc., the thickness is 0.1 to 10 mm and the density is 0.03 to 0.5.
A sheet-like styrenic resin foam of g/cc is produced.

The thickness of the sheet is preferably 0.1 to 10 mm. If the thickness is less than 0.1 mm, the sheet may be damaged during secondary foam molding, or the molded product may not have sufficient strength. Moreover, if the thickness exceeds 10 mm, secondary molding becomes difficult, which is not preferable. The density is preferably 0.03 to 0.5 g/cc. If the density is less than 0.03 g/cc, the sheet may be torn during secondary foam molding or the strength of the molded product will be insufficient, and if it exceeds 0.5 g/cc, the merits of the foamed product will be reduced, which is not preferable.

In foaming the styrene resin to obtain a styrene resin foam, nucleating agents such as talc and calcium carbonate to control the foam cell diameter, plasticizers, lubricants, pigments,
Antistatic agents, flame retardants, etc. may be used in combination. Furthermore, in order to change the surface properties of the obtained styrenic resin foam, a lubricant such as an antistatic agent, silicone, or antibacterial agent may be applied to the surface.

It is also possible to mix other styrenic resins with the specific styrenic resin used in the invention as long as the functions of the foam intended in the invention are not impaired. In order to heat and mold the styrene resin foam obtained as described above into a secondary foam, the styrenic resin foam is placed in a heating furnace, softened and secondary foamed, and then taken out of the heating furnace. Generally, it is immediately press-molded to make a molded product.

[0030] In the present invention, 10, which is a measure of the degree of polymerization,
The viscosity of the wt% toluene solution is measured using an Ostwald-Cannon-Fenske viscosity tube 50 in a constant temperature bath at 25°C. The weight percent of the structural units (A) and (B) is measured by the following method. After dissolving the styrene resin foam in methyl ethyl ketone, methanol was added and the mixture was centrifuged at 20,000 rpm for 30 min.
After processing for seconds, the precipitate (block copolymer (II)) and supernatant liquid (styrenic polymer (I)) are separated, and a large amount of methanol is added to the supernatant liquid to precipitate the styrene polymer. The styrenic polymer was dried at 200°C for 30 minutes under a reduced pressure of 5 mmHg. Using the styrene resin pretreated in this way,
1H is measured using FT-NMR under the conditions described below.

(1H measurement) Pulse width = 8.4 μs Data points = 16384 Repetition time = 7.559 seconds AD converter = 16 bits Number of integration = 1000 Sample concentration = 10 wt% Solvent = 1,1,2,2-tetra Chloroethane (d2)
Sample tube = 5 mm Measurement temperature = 120°C A peak derived from the hydrogen of the phenyl group of the structural unit (A) appears at 6.2 to 7.4 ppm. A peak derived from hydrogen in the structural unit (B) appears at 3.4 to 3.8 ppm. The weight ratio of the structural units (A) and (B) is determined from the peak area ratio.

[0032] The physical property testing methods used in the examples are described below. Melt flow rate (MFR): ISO R1133
According to. Vicat Softening Point (VICAT): ASTM D152
According to 5.

[0033]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. (Styrenic polymer-1) 5L of a raw material solution consisting of 3 parts by weight of butyl acrylate, 94 parts by weight of styrene, 2.98 parts by weight of ethylbenzene, and 0.02 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane. The mixture is continuously supplied to a complete mixing reactor and polymerized at a polymerization temperature of 120°C. The average residence time in the reactor is 5
It's time. The polymerization solution leaving the reactor is led to an extruder,
Unreacted monomers and polymerization solvent are collected from the vent and pelletized. (Styrenic Polymer-2) A styrenic polymer is obtained in the same manner as in Styrenic Polymer-1 except that 6 parts by weight of butyl acrylate and 91 parts by weight of styrene are used. (Styrenic Polymer-3) A styrenic polymer is obtained in the same manner as in Styrenic Polymer-1 except that 10 parts by weight of butyl acrylate and 87 parts by weight of styrene are used. (Styrenic polymer-4) Using an apparatus in which a complete mixing reactor (5L) and a tubular reactor (3L) were arranged in series, the polymerization temperature of the tubular reactor was 13
Operated in the same manner as styrenic polymer-3 except that the temperature was 0°C.
A styrenic polymer is obtained. (Styrenic polymer-5) Styrene 94% by weight, ethylbenzene 5.98 parts by weight,
A styrenic polymer is obtained by operating in the same manner as for styrenic polymer-4 except that the polymerization temperature in the tubular reactor is 140°C.

Table 1 shows the results of measuring the physical properties of the styrene polymer. <Production method of block copolymer> Block copolymer-1, 2, 3 A styrene-butadiene block copolymer having the polymer structure and styrene content shown in Table 2 was mixed with n-butyllithium in n-hexane. Polymerizes as an agent.

[0035]

[Examples 1 to 3, Comparative Examples 1 to 3] Using Freon-12 as a foaming agent, styrene resin having the composition shown in Table 3 was extruded and foamed to a thickness of 1.2 mm and a density of 0.10 g/cc. A sheet-like styrene resin foam is obtained. The obtained styrene resin foam is cured for 15 days, heated for 10 seconds at various temperatures using an infrared heating furnace, and subjected to secondary foaming to obtain the bento box molded product shown in FIG. 1. Next, similar secondary foaming is performed at 110° C. while changing the heating time to obtain a molded product. Table 2 shows the molding evaluation results.

[0036]

[Examples 4 to 7, Comparative Example 4] Styrenic resins having the composition shown in Table 4 were treated in the same manner as in Example 1, and the thickness was 1.
A sheet-like styrenic resin foam having a diameter of 2 mm and a density of 0.09 g/cc is obtained. A secondary foamed molded product is obtained by performing the same operation as in Example-1 except that secondary molding is performed at 100°C. Table 4 shows the appearance of the molded product and the strength measurement results.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

Effects of the Invention The styrenic resin foam of the present invention can be softened more uniformly at lower temperatures than polystyrene or polystyrene/block copolymer blend resin foams. Furthermore, since a uniform softening state can be obtained in a short time, a molded product with good productivity and no keloid-like defects can be obtained with good moldability. In addition, the strength of foamed molded products is lower than that of conventional polystyrene, styrene-butyl acrylate copolymer,
This is a significant improvement over polystyrene/block copolymer blend resin foam molded products.

The styrenic resin foam of the present invention has a significantly improved balance between secondary moldability and strength.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a bento box molded in an example of the present invention.

Claims (2)

[Claims] [Claim 1] Consisting of a structural unit represented by the following general formula (A); [Chemical 1] The following general formula (B); [Chemical 2]
The ratio of (A): 75 to 99.5% by weight (B): 0
．． 5-25% by weight (however, (A) + (B) = 100
% by weight), at least one vinyl aromatic hydrocarbon polymer block, and at least one conjugated diene-based polymer block; and conjugated diene in a weight ratio of 40:60 to 95:5 (I
A resin composition consisting of a styrenic polymer (I)
The weight ratio of I) and block copolymer (II) is 99.5:
A styrene resin foam having excellent secondary foaming moldability and strength, characterized by being formed by molding a styrene resin having a ratio of 0.5 to 85:15. [Claim 2] The thickness of the styrenic resin foam is 0.
．． 1mm~10mm, density 0.03~0.5g/cc
A styrenic resin foam having excellent secondary foaming moldability and strength according to claim 1, which is in the form of a sheet.