JPH07121998B2 - Method for producing low density polystyrene resin foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a styrene resin foam, and more specifically, it has a low density, good extrusion moldability, and good dimensional stability. And a method for producing a polystyrene resin foam having high mechanical strength.

[Problems to be solved by conventional technology and invention]

Conventionally, extruded foam of polystyrene resin can be continuously and efficiently manufactured, and its heat insulation performance, light weight, low water absorption,
Due to its workability and other characteristics, it is widely used as a heat insulating material for buildings such as general houses. However, in extrusion foaming technology, it is difficult to reduce the density because of the problems of compatibility between resin and foaming agent, maintenance of balance between resin temperature and resin pressure, balance of vapor pressure of foaming agent and resin viscosity, etc. Funny Even if the density is low, internal foaming, or so-called blowhole, occurs in the extruder, and the cells are connected in the cell structure, resulting in poor heat insulation performance.

Therefore, a method for producing a foam so-called bead foam by expanding polystyrene beads containing a foaming agent, a method for leading to a decompression device after extrusion (JP-A-59-62122,
58-63426), a method of surrounding with liquid vapor at room temperature with a large heat capacity after extrusion (JP-B-42-24071)
As a result, it has been proposed to reduce the density.

However, in the bead foam, foamed particles containing a foaming agent are foamed in several times to form a low density foam,
The particles themselves become large, and in the case of forming a molded body, it is difficult to perform airtight filling, and the foamed body has weak fusion between particles. The water resistance is inferior to that of extruded expanded polystyrene foam because water penetrates into the gaps between the beads. There are problems such as inferior dimensional stability to extruded expanded polystyrene foam.

In the method of introducing the pressure reduction device after extrusion, the pressure reduction device itself becomes extremely large-scale, it is difficult to take action on the foam for controlling the physical properties, and it is difficult to obtain the uniformity of the physical properties of the product itself. The sealing property is important for the device, but the sealing method is difficult. Depending on the sealing performance,
Even if the degree of vacuum is slightly changed, the uniformity of physical properties is affected. That is, there is a problem that the variation becomes large with respect to time and between lots.

The method of surrounding with steam with a large heat capacity is water or
Depending on the type of liquid vapor used, it is necessary to consider the material of the device. Since it requires a period or process for expelling the vapor condensate remaining in the foam, a high cost or heat loss occurs. The physical properties become non-uniform depending on the type of steam, heating temperature and amount. For example, water vapor has a gas permeation rate to polystyrene of about 4000 times that of air (N ₂ ). However, if too much steam is applied, the foam becomes too low in density to shrink at room temperature, and the condensed water is retained inside the foam, and a method for removing this is required. Further, there is a problem that the density reduction rate of the foam surface layer is increased, the density of the surface layer becomes lower than the density of the central layer, and the physical properties become nonuniform.

In addition, Japanese Patent Publication No. 59-25814 describes a method for producing a thermoplastic synthetic resin extruded foam having a low density and a small cell size. However, in this publication, a resin having a large melt index is used (it is about 9 g / 10 min according to the method described in ASTM D 1283G when estimated by conversion from the description of the examples). Thus, the low-density foam having a cell size of 0.45 mm or less obtained by using the polystyrene resin having a melt index value of 9 or more has a large dimensional change due to temperature change. For this reason, after extrusion molding, after being cut to the desired dimensions, the dimensions will be distorted, so that reprocessing is necessary, and after the construction, the dimensions will change due to temperature changes and sufficient heat insulation will occur. Does not perform well. In the foaming process, when a polystyrene resin having a melt index of 9 or more is used to obtain a low-density foam, the rigidity of the resin is weak, and thus cell breakage easily occurs,
It is difficult to obtain a good foam. Further, when a polystyrene resin having a melt index value of 9 or more is used, the density is lowered, so that the gel pressure in the system is lowered due to the mixing of a large amount of the foaming agent, and the separation phenomenon between the mixed foaming agent and the resin occurs. However, there are problems such as internal foaming and difficulty in obtaining a good thick-plate foam.

In general, a plate-shaped foam used as a heat insulating material is required to have considerably high accuracy in terms of dimensional stability as a product. For example, the dimensional change due to temperature fluctuations is limited to about ± 0.6% in use, and if it changes more than that, there is a gap after construction, the heat insulation performance is poor, and conversely, it expands and warps, so it is sufficient. Insulation performance cannot be obtained. Also, when used as a composite product, a metal plate with a small dimensional change due to temperature difference,
Peeling or warping occurs due to shear stress at the interface between plywood and mortar concrete. However, with a resin having a melt index of 9 or more, it is impossible to suppress the dimensional change due to temperature fluctuations to ± 0.6% or less when the density of the foam is reduced.

[Means for solving problems]

In view of the problems of the prior art as described above, the inventors of the present invention, by extrusion foaming method, a low density (16 kg / m ^{2 to} 23 kg / m ³ ) polystyrene-based resin foam having a thick plate shape and good dimensional stability. As a result of diligent research on the production method, a polystyrene-based resin having a low melt index value is used, and the difference between the solubility parameter value of the resin and the solubility parameter value of the foaming agent is small, that is, the foaming agent having good compatibility with the resin. Is mixed by using an injection amount having a certain relationship with the melt index value of the resin, and the average cell diameter (cell size) of the obtained polystyrene resin foam is 0.45 to 2.5 mm and the density is 16 to 23 k.
When the content is within the range of g / m ^3, the foaming agent necessary for lowering the density can be uniformly mixed and dispersed with the resin having a low melt index value without using a fluidity improver to obtain an appropriate fluidity. Therefore, it was clarified that a polystyrene-based resin foam having good extrusion moldability and having the above-mentioned characteristics can be produced, and the present invention was completed.

That is, the present invention relates to the production of a polystyrene resin foam by extruding a molten mixture containing a polystyrene resin, a foaming agent, a cell regulator and other necessary additives from a high pressure zone to a low pressure zone. As a resin, a polystyrene-based resin having a melt index value measured by the method described in ASTM-D-1238G in a range of 0.5 to 8.0 (g / 10 min) is used. 2) With a solubility parameter (δp) of the polystyrene-based resin Solubility parameter (δ
_At least one type of foaming agent having a _BA ) difference of 2 [(cal / cc) ^1/2 ] or less and the following relationship with the melt index value F (g / 10min) of polystyrene resin: 1.5-0.038F≤M _BA ≤ 3.1
Injection with an injection amount M _BA (mol / resin 1 kg) satisfying −0.038 F, and 3) injection amount W _BA (mol / resin 1 kg) of the total blowing agent containing at least one of the above-mentioned blowing agents is 1.8 <W _BA <4.0, and 4) the low density polystyrene resin foam, characterized in that the obtained polystyrene resin foam has an average cell diameter of 0.45 to 2.5 mm and a density of 16 to 23 kg / m ³ . There is a manufacturing method.

The polystyrene resin referred to in the present invention is, for example, a homopolymer of styrene derivatives such as styrene, α-methylstyrene, chlorostyrene, dichlorostyrene, dimethylstyrene, t-butylstyrene, vinyltoluene, or two kinds. It means a copolymer composed of the above combinations, a copolymer of divinylbenzene, methyl methacrylate, acrylonitrile, or a small amount of a compound which can be easily polymerized with other such as butadiene.

These polystyrene resins used in the present invention have a melt index value (MI value) of 0.5 to 8.0 (g / 10 min) measured by the method described in ASTM-D-1238G.
Must be within the range. The use of such a polystyrene-based resin enhances dimensional stability and mechanical strength as a product when a low-density thick-plate foam is obtained, and is also effective in mixing a large amount of a foaming agent. It is very important to keep the viscosity of the molten mixture at the proper viscosity.

With a polystyrene resin having an MI value of more than 8.0, when a foam having a low density (23 to 16 kg / m ³ ) is obtained, the gel pressure in the system of the extruder, mixer, and cooler is large because of the foaming agent. There is a limit to lowering the density due to the phenomenon of separation of the mixed foaming agent and resin, and because the resin film has a low rigidity and the resin rigidity is low, it is easy to cause bubble breakage, mechanical strength and dimensional stability The product is extremely inferior. As described above, in general, a plate-shaped foam used as a heat insulating material is required to have dimensional stability as a product with considerably high accuracy. For example, the dimensional change due to temperature changes is about ± 0.6% from the general usage record, and if it changes more than that,
After the construction, there is a gap and the heat insulation performance is inferior. On the contrary, when it expands, it warps, and sufficient heat insulation performance cannot be obtained.
In addition, when used as a composite product, peeling occurs or warps due to shear stress at the interface with a metal plate, plywood, or mortar concrete whose dimensional change due to temperature difference is small. On the other hand, with a polystyrene-based resin having an MI value of less than 0.5, the fluidity becomes extremely poor, and even if a compatible foaming agent is injected, the viscosity of the molten mixture is too high and the extrusion moldability is very poor at the same time. However, since the foaming efficiency is inferior, the density cannot be reduced. Therefore, the polystyrene resin used in the present invention needs to have an MI value of 0.5 to 8.0. Of these, those having an MI value of 1 to 5 are particularly preferable because they are excellent in extrusion moldability and the mechanical strength and dimensional stability of the obtained plate-like foam.

In the case of a foaming agent, the solubility parameter δ is defined by the following equation, as described on page 34 of Solvent Pocket Book (Ohm Co., Ltd., edited by The Society of Synthetic Organic Chemistry, published on July 20, 56).

δ = (CED) ^1/2 , CED = E ₁ / V CED = cohesive energy density (cal / cm ³ ) E ₁ = heat of vaporization at the boiling point (cal / mol) V = molar volume (cm ³ / mol) , The solubility parameter in the case of a polymer is such that the constitutional unit of the polymer is further subdivided and the intermolecular attractive force constant (δ
v) is calculated based on the method of estimating δ assuming additivity. An example of the solubility parameter thus obtained is shown below.

Polystyrene 9.05 (cal / cc) ^1/2 Styrene-acrylonitrile copolymer (acrylonitrile / styrene = 5/95) 9.49 (cal / cc) ^1/2 Styrene-methylmethacrylate copolymer (methylmethacrylate / styrene = 10) / 90) 9.1 (cal / cc) ^1/2 The calculation method at this time is polystyrene As an example, polystyrene has a density D: 1.05 g / cc, a molecular weight M _w = 104, and from the above-mentioned solvent pocket book, page 37, Tables 1 and 8, the intermolecular attractive force constant is Since 735 is 735, the sum of these is 896, and the solubility parameter δ is calculated by the following equation.

In the present invention, the foaming agent used includes a volatile organic foaming agent and a thermal decomposition type chemical foaming agent. For example, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, monochlorodifluoromethane, 1,1 ', 2-trichlorotrifluoroethane,
1,2-dichlorotetrafluoroethane, 1-chlorotrifluoroethane, 1-chloro-1,1'-difluoroethane, 1,1'-difluoroethane, oftafluorodichlorobutane, methyl chloride, ethyl chloride, methylene chloride, ethylene chloride , Carbon dioxide, etc.

In the method of the present invention, at least one of the blowing agents used
As the components, those having a difference in solubility parameter between the foaming agent and the resin used is 2.0 [(cal / cc) ^1/2 ] or less. Such blowing agents are typically
Hydrocarbons and halogenated hydrocarbons. As a specific example, for example, when polystyrene resin (solubility parameter of about 9) is used, trichlorotrifluoroethane,
Examples include trichloromonofluoromethane, methyl chloride and ethyl chloride. When such a foaming agent is used, the compatibility with the resin is good, and a large amount of the foaming agent can be injected, so that the foaming agent can be uniformly dispersed and mixed, and the density can be easily reduced. Further, even if a resin having a small melt index value, that is, a high viscosity as described above is used, the foaming agent improves the fluidity of the molten mixture, so that an appropriate viscosity of the molten mixture can be maintained, resulting in moldability. It is good. Also,
Since the pressure of the molten mixture can be maintained, a large foam cross-sectional area can be obtained. Furthermore, since the above foaming agent is a volatile organic foaming agent, after molding, it diffuses into the air, the plasticizing effect disappears, and the dimensional stability of the foam becomes good.

Then, in the method of the present invention, such a foaming agent is used in relation to the melt index value F [9 g / 10 min] of the resin to be used (1.5-0.038 F) to (3.1-0.0 per 1 kg of resin).
Inject in the 38F) molar range. When the injection amount is more than (-0.038F + 3.1) mol per 1 kg of resin in relation to the melt index F [(cal / cc) ^1/2 ] of the resin used, the viscosity of the molten mixture decreases. , The balance of foaming is lost (surging (ripple phenomenon)), cell destruction occurs, and it becomes a continuous foam. Also, in order to obtain an appropriate gel pressure, it is necessary to narrow the die opening,
Due to its heat insulating property, it is not possible to obtain a generally used slab-like foam having a thickness of 20 mm or more.

On the other hand, in the relationship between the injection amount and the melt index value F of the resin used, per 1 kg of resin (−0.032F + 1.
5) When it is less than the molar amount, the amount of the foaming agent having good compatibility is too small and the viscosity of the molten mixture becomes large, resulting in poor fluidity, very poor moldability, poor foaming efficiency, and low Densification becomes difficult. In addition, since the amount of the foaming agent having poor compatibility with the resin used increases, the foaming agent aggregates and internally foams, and a good foam cannot be obtained.

In the present invention, the injection amount of all the foaming agents including the above-mentioned foaming agents to be used per 1 kg of resin needs to be in the range of 1.8 mol to 4.0 mol. The use of such a large amount of blowing agent is necessary to increase the vapor pressure of the blowing agent in the molten mixture to obtain a low density foam. That is, if the polystyrene resin content is less than 1.8 mol / kg, the density of the plate-shaped foam obtained will be higher than 25 kg / m ³ , and if it is 4.0 mol or more, the extrusion moldability will be extremely poor and a good foam will not be obtained.

The preferred composition of the foaming agent is such that the difference between the solubility parameter value of the resin used and that of the foaming agent used is 2 [(cal / cc) ^1/2 ] or less, and the difference is 60 to 90 mol%. More than 2 (cal / cc) ^1/2 of the foaming agent is a mixture of 40 to 10 mol%. When the difference between the solubility parameter value of the resin used and the solubility parameter value of the used foaming agent is 2 or less, 90 mol% or more, that is, when the difference in the foaming agent exceeds 2 is 10 mol% or less. Even if a resin having a viscosity higher than that of a commonly used resin is used, since the compatibility with the resin is high, the viscosity of the melt mixture is too low, and thus extrusion foam molding cannot produce a thick plate. Further, the resin pressure at the tip of the die (die) necessary for molding cannot be maintained, bubble destruction occurs during extrusion, and moldability becomes difficult.

Even more preferably, the foaming agent used is 60 to 90 mol%
Methyl chloride, ethyl chloride or a mixture thereof,
It consists of 40 to 10 mol% of dichlorodifluoromethane, trichlorotrifluoroethane or a mixture thereof.
Methyl chloride and ethyl chloride have particularly good compatibility with polystyrene resins, so that even when mixed with a large amount of foaming agent, internal foaming caused by poor dispersion of the foaming agent does not occur. In addition, since methyl chloride and ethyl chloride have a high gas permeation rate to polystyrene resin, it is easy to escape from the inside of the foam to the outside. The dimensional stability is good because the replacement is performed. Dichlorodifluoromethane and trichlorotrifluoroethane, which have a lower thermal conductivity than air, have a low gas permeation rate for polystyrene resins and are enclosed within the foam cells, which reduces the thermal conductivity of the foam and reduces the product's thermal conductivity. Improves heat insulation. That is,
Methyl chloride, ethyl chloride, or mixtures thereof
In the range of up to 90 mol% and the content of dichlorodifluoromethane and trichlorotrifluoroethane in the range of 40 to 10 mol%, the foamed product has good extrusion moldability, dimensional stability, and thermal conductivity.

Furthermore, in the method of the present invention, it is necessary to adjust the average cell diameter (cell size) to 0.45 to 2.5 mm in obtaining a low density polystyrene resin foam within the range of 16 to 23 kg / m ³ by extrusion. There is. When trying to obtain a low-density polystyrene resin-based foam, it is not enough to regulate the type and amount of the resin and foaming agent used, as described above, and the cell size of the extruded foam is adjusted within the above range. There is a need to. Generally, when the amount of the foaming agent used increases, the cell size tends to decrease.However, when the cell size decreases, the thickness of the cell wall becomes thin and the cells become open cells during extrusion and foaming, resulting in deterioration of water vapor permeability and CFC gas. There is a problem that the thermal conductivity decreases due to diffusion, it is difficult to obtain a foam with a large thickness and a large cross-sectional area, and further, the dimensional stability decreases because the thickness of the bubble habit is not thin. . The cell size can be adjusted by the type or composition of the foaming agent used and the amount of the cell regulator such as talc used. In general, the larger the foaming agent having the higher solubility in the resin, the larger the evolution amount of the cell regulator, and the larger the cell size.

In the method of the present invention, it is preferable to use an inorganic cell regulator as the cell regulator. A polystyrene-based low-density foam using a conventional organic cell regulator (for example, indigo) reacts with an organic foaming agent and is easily dissolved and decomposed. Therefore, in order to make a uniform cell size distribution, The foaming agent used is limited. On the other hand, since the inorganic cell regulator does not have the risk of reacting with the organic foaming agent to be dissolved or decomposed, the foaming agent to be used is not limited, and the effect of obtaining a foam having a uniform cell size distribution is obtained. is there. In addition, the use of the inorganic cell adjuster allows the color of the foam and the cell size to be controlled separately, so that a foam having a small variation in color and cell size can be obtained.

Examples of the inorganic bubble regulator in the present invention include talc,
Various powders such as kaolin, calcium carbonate and barium sulfate can be used, but talc is preferred from the viewpoints of uniform air bubbles and price.

The amount of the additive used can be appropriately selected according to the cell size, but is usually 0.005 to 1.0 part by weight with respect to 100 parts by weight of the polystyrene resin.

In the method of the present invention, in addition to the above, as an additive, a flame retardant,
An ultraviolet absorber, a lubricant, and a coloring agent are appropriately added as needed.

In the method according to the present invention, the foaming agent is fed into the resin by the pouring device before feeding the resin to the extruder or after heating and melting the resin. In the extruder, the resin is melted and extruded into a kneading device. The extruded melt is passed through a kneading device, and the melt mixture is uniformly kneaded. The molten mixture is extruded from the kneading device into the high pressure zone and the low pressure zone by passing through an extrusion die. The extruded product thus extruded is molded into a plate-shaped molded body having a constant cross-sectional area by a molding device.

Here, the role of the kneading device connected between the extruder and the die is to cut the molten mixture extruded from the extruder,
By increasing the surface area, the dispersibility of the foaming agent is improved, and a large amount of the foaming agent necessary for lowering the density can be uniformly dispersed and mixed.

Next, as an example, when a polystyrene resin having a composition of F-12 / MeCl = 2 mol / 8 mol and a melt index value of 3 is used, and the residence time of the melt mixture in the kneader is about 15 minutes, If you gradually increase the injection amount of foaming agent,
FIG. 1 shows the relationship between the lowest density obtained without internal foaming and the relative speed of the stirring blade of the kneader. Thus, as the relative speed of the kneading machine is increased, the dispersibility of the foaming agent in the resin is improved, and a large amount of the foaming agent necessary for lowering the density can be injected.

The kneading capacity of the variable speed drive kneading device depends on the number of rotations of the rotor, the number of stirring blades, and the residence time of the molten mixture in the kneader. Therefore, if the residence time of the molten mixture in the kneader at a high temperature is too long, the resin will deteriorate,
Needed some technical consideration. In the present invention, however, 1) ASTM-D-1238 is used as the polystyrene resin.
The melt index value measured by the method described in G uses a polystyrene resin having a range of 0.5 to 8 (g / 10 min), and 2) a solubility parameter (δ p) of the polystyrene resin and a solubility parameter (δ _BA ). Difference of 2
[(Cal / cc) ^1/2 ] At least one of the following foaming agents is added to the polystyrene resin melt index value F (g / g
10 min) and the following relation: 1.5-0.038F ≤ M _BA ≤ 3.1-0.038F with an injection amount M _BA (mol / resin 1 kg), and 3) a total blowing agent containing at least one blowing agent as described above. By setting the injection amount W _BA (mol / resin 1 kg) within the range of 1.8 <W _BA <4.0, it became possible to knead without causing deterioration of the resin.

The kneading machine may be a variable speed drive type kneading machine as shown in FIG. 2 or a complex mixer described in JP-A-61-69428 and a cylinder housing the same around the cylinder axis. It is possible to use a mixer or the like that rotates at a low speed.

In addition, there is a limit to the amount of the foaming agent that can be dissolved in the resin, and no matter how much the kneading capacity is increased, the bubbles in the foam are destroyed due to poor dispersion, and a good foam cannot be obtained, resulting in a waste of power. Becomes

Next, an aspect of an experiment using the variable speed drive type kneader shown in FIG. 2 will be described. In the variable speed drive type kneader used here, 50 stirring blades 3 are attached in the length direction of the molten mixture on the partially hollow rotor 4 inserted in the center, and 4 in the circumferential direction. Thus, the rotor 4 is enclosed in the barrel 2. Kneading is performed by rotating the rotor 4. In FIG. 2, reference numeral 1 is a refrigerant jacket, and 5 is a pipe into which the refrigerant is inserted.

MeCl / F-113 / F-12 = 1.5 mol / 0.5 mol / 0.5 mol (MeCl is methyl chloride, F-113, F-12 are trichlorotrifluoroethane and dichlorodifluoromethane are trade names.) With composition, pressurize 2.5 mol per 1 kg of resin,
When the relative speed of the stirring blades of the kneader was 35 m / min and the residence time in the kneader of the molten mixture was 15 minutes, a polystyrene foam having a density of 19 kg / m ³ was obtained, but MeCl / F-113 / F. In the case of the foaming agent composition of −12 = 1.0 mol / 0.5 mol / 1.0 mol, blowholes, that is, internal foaming occurred and the foam was a continuous foam when the relative speed of the stirring blade of the kneader was 35 m / min. However, by setting it to 40 m / min, a foam with good closed cells was obtained. Thus, when the amount of the foaming agent having poor compatibility was increased, a good foam was obtained by increasing the relative speed of the stirring blades of the kneader, that is, by increasing the kneading ability. For these reasons, the injection amount of blowing agent is 1 kg of resin.
The current limit is about 4.0 mol.

〔Example〕

Example 1 Polystyrene 1 having a melt index value (MI value) of 1.1 g / 10 min and a solubility parameter value of 9.05 (cal / cc) ^1/2
00 parts by weight, 0.1 parts by weight of talc as a bubble control agent
It is fed to a 0 mmφ screw extruder at a rate of 500 kg per hour, and further, as a foaming agent, methyl chloride per 1 kg of the polystyrene (solubility parameter value = 9.7 (cal
/ cc) ^1/2 ) 2 mol, trichlorotrifluoroethane (solubility parameter value = 7.4 (cal / cc) ^1/2 ) 1 mol, dichlorodifluoroethane (solubility parameter value = 6.6 (cal / cc) ^1/2 ) ) Was injected through a 0.6 mol blowing agent injection port.

Subsequently, the melt was passed through a variable speed rotor-driven mixer (45 m / min) connected between the extruder and the slit die, and the uniformly kneaded melt mixture was slit die (width 20 mm).
From 0 mm x 3 mm gap) at 120 ° C, extrude into the atmosphere,
Through a molding device, it was molded into a thick plate foam having a thickness of 50 mm and a width of 600 mm. During the above manufacturing process, the observed extrusion moldability and various physical properties of the test piece along with various conditions
The results are shown in Table 4.

In each table, 1) The MI value of the resin used was measured according to ASTM-D-1238G.

2) The density of the foam is a value measured after standing for 3 days at 20 ° C. after extrusion molding.

3) The average cell size of the foam is a value measured according to ASTM-3576-77.

4) The compressive strength of the foam is the strength in the thickness direction measured according to JIS A 9511 after standing for 5 days at 20 ° C. after extrusion molding.

5) The thermal conductivity of the foam is a value measured according to JIS A 9511 after standing for 7 days at 20 ° C. after extrusion molding.

6) The dimensional change in the length and width directions of the foam is the change from the original size when heated to 70 ° C in an oven after being left for 7 days at 20 ° C (-indicates shrinkage). , And + represents elongation).

7) As for the cell size distribution of the foam, the cell cross section of the foam is divided into three in the thickness direction, and the cell size of the outer layer part and the center part is 3).
The measurement was performed in the same manner as above and the difference was evaluated as follows.

○ Difference of 0.05 mm or less △ Difference of 0.05 mm to 0.1 mm × Difference of 0.1 mm or more Examples 2 to 19 and Comparative Examples 1 to 18 Mixed foaming agents having compositions shown in Tables 1 to 4 and polystyrene having a melt index value The same procedure as in Example 1 was performed except that the amounts of talc and indigo were used.

Evaluation test In the case of wooden houses, the space between joists for floor use is generally 260 mm for Western-style rooms and 410 mm for Japanese-style rooms. is there. However, due to the carpenter's construction error, there is an error of about ± 5 mm in this interval. Therefore, for the foams of Examples 13 to 15 and Comparative Examples 14 and 15, samples 10 mm wider than the joist spacing (width 270 m
An insertion test was performed using m × thickness 25 mm × length 910 mm and width 420 mm × thickness 5 mm × length 910 mm).

The results are shown in Table 5. In the evaluation, cracked ones were evaluated as ×, cracked ones were evaluated as Δ, and good ones were evaluated as ○.

From this evaluation test, in terms of insertability, the density range is 25 kg / m ³
The following is preferable, but 22 kg / m ³ or less is more preferable.

〔The invention's effect〕

According to the present invention, it is possible to produce a plate-like foam having a uniform density in a cross section, little color unevenness between lots, and good dimensional stability while having a low density of 16 to 25 kg / m ^{3 in} a density range. The plate-like foam is lightweight, has excellent heat insulating properties, has good workability, and has excellent secondary workability such as cutting.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the rotor speed of the kneading device and the minimum density at which internal foaming does not occur, and FIG. 2 (a).
(A) is a sectional view of a variable speed drive type kneading device. 1 ... Refrigerant jacket, 2 ... Cooler, 3 ... Blade, 4 ... Rotor inserted in the center, 5 ... Pipe for inserting refrigerant.

Claims (5)

[Claims] 1. A method for producing a polystyrene resin foam by extruding a molten mixture containing a polystyrene resin, a foaming agent, a cell regulator and other necessary additives from a high pressure zone to a low pressure zone. 1) Polystyrene resin The melt index value measured by the method described in ASTM-D-1238G is 0.
Using polystyrene resin in the range of 5 to 8.0 (g / 10min), 2) the difference between the solubility parameter (δp) and the solubility parameter (δ _BA ) of polystyrene resin is 2 [(cal / c
c) ^1/2 ] or less of at least one foaming agent, and the injection amount that satisfies the following relationship with the melt index value F (g / 10min) of the polystyrene resin 1.5-0.038F ≤ M _BA ≤ 3.1-0.038F _MBA (mol / resin 1 kg), 3) The total amount of the blowing agent containing at least one foaming agent W _BA (mol / resin 1 kg) is within the range of 1.8 <W _BA <4.0, and 4) Determine the average cell diameter of the obtained polystyrene resin foam
A method for producing a low-density polystyrene-based resin foam, which has a density of 0.45 to 2.5 mm and a density of 16 to 23 kg / m ³ . 2. The composition of all the foaming agents is such that the difference between the solubility parameter value of the resin used and the solubility parameter value of the foaming agent used is 2 [(cal / cc) ^1/2 ] or less and 60 to 60 9
0 mol%, a mixture of 40 to 10 mol% of a blowing agent whose difference exceeds 2 [(cal / cc) ^1/2 ], and the molten mixture was connected to them between the extruder and the die. The method according to claim 1, wherein kneading is performed by a kneading device. 3. The total blowing agent comprises 60 to 90 mol% of methyl chloride, ethyl chloride or a mixture thereof, and 40 to 10 mol%.
A process according to claim 2 which is essentially dichlorofluoromethane, trichlorotrifluoroethane or a mixture thereof. 4. As the polystyrene resin, ASTM-D
Melt index value measured by the method described in -1238G uses a polystyrene resin having a range of 1.0 to 5.0 (g / 10 min), The method according to claim 1, 2 or 3. . 5. The method according to any one of claims 1 to 4, wherein an inorganic cell regulator is used as the cell regulator.