JP2015189815A - Polystyrene-based resin foam sheet and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam sheet having satisfactory appearance, excellent dimensional stability, and flexibility and having cushioning properties, and a method for producing the foam sheet.SOLUTION: There is provided a polystyrene-based resin foam sheet in which thickness is 1.0 to 10 mm, the ratio of the surface layer density d2 from the surface to a depth of 0.2 mm, to the total density d1 (d2/d1) is 0.8 to 1.8, and an open cell ratio is 9 to 30 vol.%. There is also provided a method for producing the polystyrene-based resin foam sheet including a process where a polystyrene-based resin foam sheet is heated with vapor so as to be foamed to obtain a polystyrene-based foam sheet, in which the polystyrene-based resin foam sheet has a thickness of 0.5 to 5.0 mm, and in which the ratio of the surface layer density d4 from the surface to a depth of 0.2 mm, to the total density d3 (d4/d3) is 1.0 to 1.8, and an open cell ratio is 5 to 26 vol.%.

Description

  The present invention relates to a polystyrene-based resin foam plate and a method for producing the same.

  Polystyrene resin foam plates (hereinafter simply referred to as foam plates) are widely used in various applications such as cushioning materials, toys such as model airplanes, POP display substrates, and the like. The foamed plate can be obtained by secondarily foaming a polystyrene resin foam sheet (hereinafter simply referred to as a foam sheet) obtained by first foaming a melt-kneaded product containing a polystyrene resin and a foaming agent.

Specific examples of the foam plate include the following.
(I) A foamed plate obtained by heating and foaming a foam sheet having a thickness of 0.1 to 5 mm obtained by a T-die method or an inflation method with water from above and below with an endless wire mesh (Patent Document 1).
(Ii) A foamed plate obtained by bringing water vapor into contact with both front and back surfaces of a foamed sheet obtained by extrusion foaming, heating and foaming (Patent Document 2).

  In the foamed plates (i) and (ii), the surface shape may be uneven, resulting in poor appearance. Moreover, the dimension after manufacture may change because thickness shrinks after manufacture or tertiary foaming occurs. Further, the surface hardness becomes too high, the flexibility becomes insufficient, and the buffering property may be inferior.

By the way, as a raw material for thermoforming, a foam sheet having a thickness of 0.5 to 5 mm, an apparent density of 70 to 150 kg / m ³ , and an open cell ratio of 0 to 15% by volume has been proposed (patent) Reference 3). However, when the foamed sheet is used as the raw material of the foamed plate and is foamed by steam foaming (secondary foaming), corrugation occurs and the flat foamed plate is not formed, resulting in poor appearance.

Japanese Examined Patent Publication No. 45-29394 JP 63-122515 A JP 2007-217711 A

  An object of the present invention is to provide a foamed plate having a good appearance, excellent dimensional stability, flexibility, and buffering properties, and a method for producing the foamed plate.

  The foamed plate of the present invention has a thickness of 1.0 to 10 mm, and the ratio (d2 / d1) of the surface layer density d2 from the surface to the depth of 0.2 mm with respect to the total density d1 is 0.8 to 1.8. Yes, the open cell rate is 9 to 30% by volume.

  The foamed plate of the present invention preferably has an elastic modulus of 10 to 30 MPa when a three-point press bending test is performed in accordance with JIS K7171-2008.

  The method for producing a foamed plate according to the present invention is a method for producing the foamed plate according to the present invention, and includes a step of heating the foamed sheet with steam to obtain a foamed plate, The thickness is 0.5 to 5.0 mm, the ratio (d4 / d3) of the surface layer density d4 from the surface to the depth of 0.2 mm to the total density d3 is 1.0 to 1.8, and the open cell ratio Is 5 to 26% by volume.

  In the manufacturing method of the foam board of this invention, it is preferable that the said steam is water vapor | steam.

The foamed board of the present invention has a good appearance, excellent dimensional stability, flexibility, and buffering properties.
Moreover, according to the method for producing a foamed plate of the present invention, a foamed plate having good appearance, excellent dimensional stability, flexibility, and buffering properties can be obtained.

It is the schematic diagram which showed an example of the manufacturing method of the foamed board of this invention. It is the schematic diagram which showed the other example of the manufacturing method of the foam board of this invention.

  In this specification, the “surface layer” of the foam plate means a layer having a depth of 0.2 mm from the surface of the foam plate. Similarly, the “surface layer” of the foam sheet means a layer having a depth of 0.2 mm from the surface of the foam sheet.

<Foam board>
The foamed plate of the present invention is a plate-like foam containing a polystyrene resin, so-called polystyrene paper (PSP).
The foamed plate of the present invention has a thickness of 1.0 to 10 mm, and the ratio (d2 / d1) of the surface layer density d2 from the surface to the depth of 0.2 mm with respect to the total density d1 is 0.8 to 1.8. Yes, the open cell ratio is 9 to 30% by volume. However, the surface layer density d2 is an average value of the surface layer densities of both surfaces of the foamed plate.
By controlling the thickness, the ratio (d2 / d1) and the open cell ratio within the above ranges, unevenness in the surface shape is suppressed, a flat and good appearance is obtained, and shrinkage and tertiary foaming occur after production. It becomes difficult to obtain a foamed plate having excellent dimensional stability. Further, the surface hardness is not excessively high, and the foamed plate has flexibility and cushioning properties.

  The thickness of the foam is 1.0 to 10 mm, preferably 1.0 to 8.0 mm, and more preferably 1.0 to 7.0 mm. If the thickness of the foam is equal to or greater than the lower limit value, the foam has a good appearance and has excellent dimensional stability. If the thickness of the foam is not more than the above upper limit value, there is flexibility and weight reduction is facilitated.

  The ratio (d2 / d1) of the surface layer density d2 to the overall density d1 of the foamed plate is 0.8 to 1.8, preferably 0.8 to 1.7, and more preferably 0.8 to 1.6. If ratio (d2 / d1) is more than the said lower limit, it will become a foam board with the favorable external appearance and the outstanding dimensional stability. If ratio (d2 / d1) is below the said upper limit, it will become a flexible foam board.

Overall density d1 of the foam plate is preferably 0.03~0.15g / cm ^3, more preferably 0.035~0.09g / cm ^3, more preferably 0.04~0.08g / cm ^3. If the overall density d1 is equal to or more than the lower limit value, it is easy to obtain a foamed plate having good appearance and excellent dimensional stability. If the overall density d1 is equal to or less than the upper limit value, a flexible foam plate is likely to be obtained.

Surface density d2 of the foam plate is preferably 0.03~0.15g / cm ^3, more preferably 0.035~0.12g / cm ^3, more preferably 0.04~0.10g / cm ^3. When the surface layer density d2 is equal to or higher than the lower limit value, it is easy to obtain a foamed plate having a good appearance and excellent dimensional stability. If surface layer density d2 is below the said upper limit, it will become a flexible foam board easily.

  The open cell ratio of the foamed plate is 9 to 30% by volume, preferably 10 to 28% by volume, and more preferably 10 to 25% by volume. When the open cell ratio of the foam is not less than the lower limit, the foamed plate is flexible and has a buffering property. When the open cell ratio of the foam is within the above range, the foam has a good appearance and has excellent dimensional stability.

  50-75 are preferable and, as for the surface hardness of a foamed board, 53-73 are more preferable. If the surface hardness of the foamed plate is equal to or higher than the lower limit, excellent dimensional stability is easily obtained. If the surface hardness of the foamed plate is not more than the above upper limit value, the foamed plate is flexible and easily has a good cushioning property.

The basis weight of the foam plate is preferably ^{75~400g / m 2, 100~350g / m} 2 is more preferable. If the basis weight of the foamed plate is equal to or greater than the lower limit value, it is easy to maintain the strength of the foamed plate. If the basis weight of the foamed plate is equal to or less than the above upper limit value, the foamed plate is flexible and easily has a cushioning property.

100-650 kPa is preferable and, as for the maximum point stress of a foamed board, 150-600 kPa is more preferable. If the maximum point stress of the foamed plate is equal to or greater than the lower limit, the strength of the foamed plate is easily maintained. If the maximum point stress of the foamed plate is equal to or less than the upper limit, the foamed plate is flexible and easily has a buffering property.
The maximum point stress means the maximum point stress when a three-point press bending test is performed in accordance with JIS K7171-2008.

The elastic modulus of the foamed plate is preferably 10 to 30 MPa, and more preferably 12 to 25 MPa. If the elastic modulus of the foamed plate is equal to or higher than the lower limit, the strength of the foamed plate is easily maintained. If the elastic modulus of the foamed plate is not more than the above upper limit value, the foamed plate is flexible and easily has a buffering property.
The elastic modulus means an elastic modulus when a three-point press bending test is performed in accordance with JIS K7171-2008.

The polystyrene resin is not particularly limited, and examples thereof include homopolymers or copolymers of styrene monomers. In addition, the polystyrene resin includes a copolymer having a styrene monomer as a main component, which is a copolymer of a styrene monomer and a vinyl monomer copolymerizable with the styrene monomer. A coalescence may be used.
As the polystyrene-based resin, a polystyrene-based resin having 50% by mass or more of structural units based on styrene with respect to all the structural units is preferable, and polystyrene is more preferable.

Examples of the styrene monomer include styrene, α-methyl styrene, vinyl toluene, chlorostyrene, ethyl styrene, i-propyl styrene, dimethyl styrene, bromostyrene, and the like.
A styrene-type monomer may be used individually by 1 type, and may use 2 or more types together.

Examples of vinyl monomers copolymerizable with styrene monomers include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate. Bifunctional monomers such as (meth) acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, divinyl benzene, alkylene glycol dimethacrylate, and the like.
A vinyl-type monomer may be used individually by 1 type, and may use 2 or more types together.

The polystyrene resin used as a raw material can be a commercially available polystyrene resin, a polystyrene resin produced by a method such as suspension polymerization, a polystyrene resin that is not a recycled material (virgin polystyrene), a used foamed plate, Recycled raw materials obtained by reclaiming polystyrene-based resin foam molded articles (such as food packaging trays) can be used. As the recycled material, it is possible to use a recycled material obtained by recovering a used foamed plate or polystyrene-based resin foam-molded product and regenerating it by a limonene dissolution method or a heating volume reduction method.
Polystyrene resins may be used alone or in combination of two or more.

  In the foam of this invention, you may mix | blend another resin with a polystyrene resin in the range which has a polystyrene resin as a main component. That the polystyrene resin is a main component means that the ratio of the polystyrene resin to the total resin component (100% by mass) of the foam is 50% by mass or more.

Examples of polystyrene resins blended with other resins include diene rubber polymers (polybutadiene, styrene-butadiene copolymer, ethylene-propylene-nonconjugated diene) for improving the impact resistance of foamed plates. Examples thereof include rubber-modified polystyrene resins blended with a three-dimensional copolymer or the like), so-called high impact polystyrene.
Examples of other resins include polyethylene resins, polypropylene resins, acrylic resins, acrylonitrile-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, and the like.

Further, as other resins, polyphenylene ether resins may be used. By blending a polyphenylene ether-based resin with a polystyrene-based resin, the foamed plate is superior in toughness, hard to break, excellent in strength, and also excellent in heat resistance, compared to the case where the polystyrene-based resin is used alone.
When blending a polyphenylene ether resin with a polystyrene resin, the ratio of the polyphenylene ether resin is preferably 5% by mass or more and less than 50% by mass, and 10 to 40% by mass with respect to the total resin component (100% by mass). More preferred.
Another resin may be used individually by 1 type, and may use 2 or more types together.

  The foamed plate of the present invention has a nucleating agent, a crosslinking agent, a filler, a flame retardant, a flame retardant aid, a lubricant (hydrocarbon, fatty acid, fatty acid amide, ester, alcohol within the range not impairing the physical properties. System, metal soap, silicone oil, wax such as low molecular weight polyethylene, etc.), spreading agents (liquid paraffin, polyethylene glycol, polybutene, etc.), colorants and other additives may be added. Especially, it is preferable that the foamed board of this invention contains a nucleating agent.

Examples of the nucleating agent include talc, sodium hydrogen carbonate, ammonium hydrogen carbonate, calcium carbonate, clay, citric acid and the like. Of these, talc is preferable as the nucleating agent. A nucleating agent may be used individually by 1 type, and may use 2 or more types together.
The addition amount of the nucleating agent is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the polystyrene resin.

Paper or a resin film can be laminated on at least one surface of the foamed plate of the present invention. By laminating paper or a resin film on the surface of the foamed plate, the surface can be made more beautiful and the rigidity can be made higher.
The resin film can be colored in various colors by adding colorants (pigments, dyes, etc.), and various patterns and designs can be displayed by printing on the surface. Similarly, various patterns and designs can be displayed by printing on the paper surface.
What laminated | stacked paper or the resin film on the surface of the foamed board can be used for the display substrate for POP, for example.

  The material of the resin film laminated on the foam plate is not particularly limited. For example, heat such as polystyrene resin, impact-resistant polystyrene resin, polyethylene resin, polypropylene resin, acrylic resin, polylactic acid resin, etc. A plastic resin is mentioned.

As for the thickness of the paper or resin film laminated | stacked on a foamed board, 10-100 micrometers is preferable.
Examples of the paper lamination method include a method of laminating with an adhesive such as a hot melt adhesive.
As a method of laminating the resin film, a thermoplastic resin in a molten state is extruded into a film shape on the surface of the foamed plate and thermally fused, or the resin film is superimposed on the foamed plate and adhered by thermal fusion or an adhesive. Methods and the like.

  The foamed plate of the present invention described above has a good appearance and is dimensioned after production because the thickness, the ratio of the surface layer density d2 to the overall density d1 (d2 / d1), and the open cell ratio are controlled within a specific range. Is difficult to change, has excellent dimensional stability, is flexible, and has excellent buffering properties.

<Method for producing foam plate>
As a manufacturing method of the foam board of this invention, the method of having the following primary foaming process and secondary foaming process is mentioned, for example.
Primary foaming step: a step of obtaining a foamed sheet (primary sheet) by extruding a melt-kneaded material obtained by melt-kneading at least a polystyrene resin and a foaming agent from an extruder and foaming (primary foaming).
Secondary foaming step: a step of heating a foamed sheet with steam to foam (secondary foaming) to obtain a foamed plate.

[Primary foaming process]
In the primary foaming process, for example, polystyrene resin, and other resins used as necessary, nucleating agent, etc. are supplied to the extruder, melted by heating, added with the foaming agent, kneaded, and attached to the tip of the extruder Foaming (primary foaming) is performed while extruding from the obtained mold, and the obtained foamed sheet (primary sheet) is wound up and collected. The recovered foam sheet becomes a raw sheet of the foam plate.

As the foaming agent, a physical foaming agent is preferable.
As the physical foaming agent, hydrocarbons having 6 or less carbon atoms (for example, aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, and cyclopentane) are preferable, and normal butane, isobutane, normal pentane, and isopentane. Is more preferable. A foaming agent may be used individually by 1 type, and may use 2 or more types together.
1.0-6.0 mass parts is preferable with respect to 100 mass parts of all the resin components to be used, and 1.5-5.0 mass parts is more preferable.

As a metal mold | die attached to the front-end | tip of an extruder, the cyclic | annular metal mold | die (circular die) which has cyclic | annular opening, T-die, etc. are mentioned, for example.
As a specific aspect in the case of using the annular mold, for example, while cooling the cylindrical foam extruded from the annular mold along the cooling mandrel, cooling is performed by blowing cooling air to the outer surface of the cylindrical foam, A mode in which the cylindrical foam is cut in an axial direction with a cutter provided on both sides of the front end portion of the cooling mandrel is cut into two foam sheets.

  The expansion ratio in primary foaming is preferably 7 to 15 times, and more preferably 9 to 12 times. If the expansion ratio in primary foaming is equal to or greater than the lower limit, the foamed plate can be easily reduced in weight. If the expansion ratio in primary foaming is less than or equal to the above upper limit value, it is easy to obtain a foam plate having high strength.

In the primary foaming step, the obtained foamed sheet satisfies the following conditions: thickness, overall density d3, ratio of surface layer density d4 from the surface to a depth of 0.2 mm (d4 / d3), and open cell ratio It is preferable to control the production conditions.
For example, the thickness of the foam sheet can be controlled by adjusting the amount of the foaming agent. Moreover, the ratio (d4 / d3) of a foam sheet can be made smaller by making the temperature of a metal mold | die higher. Moreover, the open cell ratio of a foamed sheet can be made high by raising the temperature after melting a polystyrene-type resin.

[Secondary foaming process]
In the secondary foaming process, for example, as shown in FIG. 1, the foamed sheet 1 is sent out from the foamed sheet roll 10 obtained in the primary foaming process and continuously passed through the steam foaming tank 14 by the guide roll 12. It is conveyed and heated by steam in the steam foaming tank 14 to be foamed (secondary foaming). Next, the foamed plate 2 obtained by secondary foaming is cooled by a cooling roll 16 and cut into a predetermined size by a cutting machine 18.
The method of secondary foaming by heating the foamed sheet with steam is easy to increase the foaming ratio and easily obtain a low density foamed board, and more flexible and excellent cushioning can be obtained. Is advantageous. In the present invention, it is particularly preferable to use water vapor as the vapor because the compatibility with the polystyrene resin is good and the foamed sheet can be sufficiently subjected to secondary foaming.

(Foam sheet)
The foam sheet used in the secondary foaming process has a thickness of 0.5 to 5.0 mm, a ratio of the surface layer density d4 to the total density d3 (d4 / d3) of 1.0 to 1.8, and an open cell ratio. Is preferably 5 to 26% by volume.
By subjecting the foamed sheet to secondary foaming, it is possible to obtain a foamed plate having an increased thickness, a higher density, and an increased open cell ratio.

By appropriately increasing the open cell ratio of the foam sheet, it becomes easy for vapor to easily enter the foam sheet. Further, by making the surface density d4 of the foamed sheet closer to the overall density d3, that is, by making the ratio (d4 / d3) closer to 1.0, it becomes easier for vapor to easily enter the foamed sheet. Therefore, when the foamed sheet satisfies the above-mentioned conditions, the foamed sheet can be easily subjected to secondary foaming at a sufficient foaming ratio, and the appearance satisfying the aforementioned conditions of thickness, ratio (d2 / d1) and open cell ratio It becomes easy to obtain a foamed plate having good and excellent dimensional stability.
Moreover, if the foamed sheet satisfies the above-mentioned conditions, a foamed plate having more excellent flexibility and excellent buffering properties can be obtained.

  The thickness of the foamed sheet is preferably 0.5 to 5.0 mm, more preferably 0.9 to 4.0 mm, and further preferably 1.0 to 3.7 mm. If the thickness of the foamed sheet is equal to or more than the lower limit, a foamed plate having a good appearance and excellent dimensional stability can be easily obtained. If the thickness of the foamed sheet is not more than the above upper limit value, it is easy to obtain a foamed plate having better flexibility and excellent buffering properties, and the foamed plate can be easily reduced in weight.

  The ratio (d4 / d3) of the surface layer density d4 to the overall density d3 of the foamed sheet is preferably 1.0 to 1.8, more preferably 1.0 to 1.7, and still more preferably 1.0 to 1.6. . If the ratio (d4 / d3) is equal to or greater than the lower limit, a foamed plate having a good appearance and excellent dimensional stability can be easily obtained. If the ratio (d4 / d3) is less than or equal to the above upper limit value, the vapor enters the foamed sheet more uniformly, and secondary foaming is facilitated at a sufficient foaming ratio. Moreover, it is easy to obtain the foam board which is excellent in a softness | flexibility and has the outstanding buffer property.

The total density d3 of the foamed sheet is preferably 0.04 to 0.20 g / cm ³ , more preferably 0.05 to 0.18 g / cm ³ , and even more preferably 0.05 to 0.15 g / cm ³ . If the overall density d3 is equal to or greater than the lower limit, it is easy to obtain a foamed plate having good appearance and excellent dimensional stability. If the overall density d3 is less than or equal to the above upper limit value, the vapor enters the foamed sheet more uniformly, and secondary foaming is facilitated at a sufficient foaming ratio. Moreover, it is easy to obtain the foam board which is excellent in a softness | flexibility and has the outstanding buffer property.

The surface density d4 of the foamed sheet is preferably 0.04 to 0.25 g / cm ³ , more preferably 0.05 to 0.23 g / cm ³ , and even more preferably 0.05 to 0.20 g / cm ³ . When the surface layer density d4 is equal to or higher than the lower limit value, it is easy to obtain a foamed plate having good appearance and excellent dimensional stability. If the surface layer density d4 is less than or equal to the above upper limit value, the vapor enters the foamed sheet more uniformly, and secondary foaming is facilitated at a sufficient foaming ratio. Moreover, it is easy to obtain the foam board which is excellent in a softness | flexibility and has the outstanding buffer property.

  The open cell ratio of the foamed sheet is preferably 5 to 26% by volume, more preferably 5 to 23% by volume, and still more preferably 5 to 20% by volume. If the open cell ratio of the foamed sheet is equal to or greater than the lower limit, it is easy for steam to enter the foamed sheet, and it becomes easy to obtain a foamed sheet having a sufficient thickness that is secondarily foamed at a sufficient foaming ratio. Moreover, it is easy to obtain the foam board which is excellent in a softness | flexibility and has the outstanding buffer property. If the open cell ratio of the foamed sheet is not more than the above upper limit value, it is easy to obtain a foamed plate with good appearance and excellent dimensional stability.

  In the secondary foaming process, it is preferable to use the foamed sheet obtained in the primary foaming process for secondary foaming after aging under atmospheric pressure conditions. In the foam sheet immediately after the primary foaming, the volume of the gaseous foaming agent present in the formed bubbles contracts due to cooling, so that the inside of the bubbles is in a reduced pressure state and secondary foaming hardly occurs. By aging the foam sheet, air enters the bubbles from the outside of the sheet, and the bubbles are in an atmospheric pressure state. This facilitates secondary foaming of the foamed sheet at a sufficient foaming ratio. Moreover, since the bubbles of the foamed plate are less likely to shrink after secondary foaming, the dimensional stability of the foamed plate becomes better.

  80-120 degreeC is preferable and, as for the temperature in a steam foaming tank, 90-110 degreeC is more preferable.

  In the foam plate manufacturing method of the present invention described above, the foam is obtained because the foam plate has a thickness, a ratio of the surface layer density d2 to the total density d1 (d2 / d1), and an open cell ratio controlled within a specific range. The plate has a good appearance, excellent dimensional stability, and excellent buffering properties.

In addition, the manufacturing method of the foamed board of this invention is not limited to an above described manufacturing method.
In the method for producing a foamed plate of the present invention, paper or a resin film may be laminated on the surface of the foamed plate subjected to secondary foaming.
Specifically, for example, the following method may be used. As shown in FIG. 2, the foamed sheet 1 is sent out from the foamed sheet roll 10, and is heated and foamed (secondary foaming) by steam while passing through the steam foaming tank 14 by the guide roll 12. Thereafter, the paper 3 with an adhesive is fed out from a pair of paper rolls 20 and stacked on both surfaces of the foamed plate 2, heated and bonded by a hot roll 22 for bonding to form a laminate 4, cooled by a cooling roll 16, and a cutting machine. 18 is cut into a predetermined size. When laminating a resin film, instead of the paper roll 20, a resin film made of the same material as the foam plate is used, or a resin film roll around which a resin film with an adhesive is wound is used. Lamination can be performed in the same manner as in the above.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[Measurement of basis weight]
The portion excluding both ends 20 mm in the width direction of the foamed sheet was cut into 10 cm × 10 cm at equal intervals in the width direction, and the mass (g) of each slice was measured to 0.001 g unit. A value obtained by converting an average value of the mass (g) of each section into a mass per 1 m ² was defined as a basis weight (g / m ² ) of the foamed sheet. It measured similarly about the basic weight of a foamed board.

[Measurement of thickness]
Using a dial thickness gauge SM-112 (manufactured by Tecrock Co., Ltd.), measure the thickness of 9 or more points at equal intervals in the width direction at the portion of the foam sheet excluding the 20 mm end region from both edges in the width direction. And the arithmetic mean of those was made into thickness. The thickness of the foam plate was also measured in the same manner.

[Measurement of open cell ratio]
The open cell ratio of the foamed sheet was measured by the 1-1 / 2-1 atmospheric pressure method in accordance with ASTM D-2856-87.
Specifically, the foam sheet was cut into a flat square shape with a side of 25 mm, and a plurality of the cut pieces were overlapped in the thickness direction to prepare a test piece having a thickness of about 25 mm. A total of 5 test pieces were prepared in the same manner, and each test piece was continuously measured by the 1-1 / 2-1 atmospheric pressure method using an air-comparing hydrometer (manufactured by Tokyo Science Co., Ltd., trade name “1000 type”). The bubble rate was measured. From the volume V _{0 of the} test piece calculated from the size measured with the caliper and the volume V _{0 of} the test piece measured by the 1-1 / 2 atm method, the open cell ratio Z of each test piece is obtained from the following equation (1). (Vol%) was calculated, and the arithmetic mean value thereof was defined as the open cell ratio of the foam sheet.
Z = (V ₀ −V) / V ₀ × 100 (1)
The open cell ratio of the foamed plate was measured in the same manner.

[Measurement of total density]
Nine or more 10 cm × 10 cm rectangular sections are cut out at equal intervals in the width direction of the sheet from the portion excluding the end area of 20 mm from both edges in the width direction of the foam sheet, and the mass W of each section _A (g) was measured. Further, the thickness of each section was measured using a dial thickness gauge SM-112 (manufactured by Teclock Co.), and the volume _VA (mm ³ ) of each section was calculated. The density d _A (g / cm ³ ) of each section was calculated by the following formula (2), and the value obtained by arithmetically averaging the density d _{A of} each section was defined as the overall density d3 of the foam sheet.
d _A = W _A / V _A × 10 ³ (2)
The total density d1 of the foamed plate was measured in the same manner.

[Measurement of surface layer density]
Using a slicer (Split machine manufactured by Fortuna (Germany), model AB-320-D), cut off the surface layer (thickness 0.2 mm) on both sides of the foamed sheet, and cut it into a width of 25 mm and a length of 150 mm for measurement test It was a piece. The mass W _B (g) and the volume V _B (mm ³ ) of the test specimen for measurement are measured in the same manner as in the case of measuring the total density, and the surface layer density d4 (g / cm ³ ) of the foamed sheet is obtained from the following formula (3). ) Was calculated.
d4 = W _B / V _B × 10 ³ (3)
However, the test specimen for measurement was cut from a foam sheet that had passed 72 hours or more after molding, and was left for 16 hours or more in an atmosphere of 23 ± 2 ° C., 50 ± 5 RH%, or 27 ± 2 ° C., 65 ± 5 RH%. Was used for the measurement.
The surface layer density d2 of the foam plate was also measured in the same manner.

[Measurement of surface hardness]
The surface hardness of the foamed board obtained in each example was measured by the following method.
A value obtained when a test piece having a width of 130 cm and a length of 50 cm is cut out from the foamed plate and the surface hardness tester is pressed against the surface of the test piece using an Asker surface hardness tester (model: “CS type”, manufactured by Asker). Was measured as surface hardness. In addition, the measurement is performed every 20 cm in the width direction and every 15 cm in the extrusion direction in the test piece, and the arithmetic average thereof is defined as the surface hardness.

[Appearance evaluation]
The obtained foam board was confirmed visually and the external appearance was evaluated according to the following criteria.
○ (Good): No unevenness and smoothness.
X (defect): There is uneven unevenness and there is no smoothness.

[Measurement of maximum point stress and elastic modulus]
In accordance with JIS K7171-2008, the maximum point stress and elastic modulus of the foamed plate were measured.
Specifically, a three-point press bending test was performed using a Tensilon universal testing machine (trade name “RTG-1310” manufactured by A & D Co., Ltd.). The measurement conditions are shown below.
Test piece size: 50 mm × 150 mm.
Distance between jigs: 100 mm.
Compression jig: an indenter having a tip dimension (R) of 5 mm, and a support base having a width of 100 mm having a 5 ° inclination starting from a portion in contact with the test piece.
Compression speed: 50 mm / min.
Push bending distance: 30 mm.
Data processing system for general-purpose tester manufactured by A & D, Inc. The three-point push bending test is performed with the thickness, width, and length of the test piece entered in the MSAT0002RTF / RTG program, and is automatically calculated. The maximum point stress (kPa) and elastic modulus (MPa) were obtained as data.

[Evaluation of dimensional change]
Two straight lines having a length of 100 mm were drawn on the surface of the foamed plate immediately after vapor foaming (secondary foaming) so as to be orthogonal to each other. Any one straight line was made parallel to the extrusion direction. Next, the foamed plate was allowed to stand for 1 week in an atmosphere of 23 ° C. ± 3 ° C. and humidity 60% ± 5%, and then the length L of each of the two straight lines was measured. The dimensional change rate (%) was calculated based on the above, and the arithmetic average value of the two dimensional change rates was taken as the dimensional change rate.
Dimensional change rate (%) = 100 × (L−100) / 100
The dimensional change was evaluated according to the following criteria.
○ (Good): The dimensional change rate is 1% or less after one week from the steam foaming.
X (defect): The dimensional change rate exceeds 1% after one week from the steam foaming.

[Comprehensive evaluation]
Comprehensive evaluation was performed according to the following criteria.
◯: Overall evaluation is good when all items are good (◯).
×: If there is a defect (×) even in one item, the overall evaluation is poor.

[Example 1]
97.8% by mass of polystyrene resin (trade name “HRM-26” manufactured by Toyo Styrene Co., Ltd.) and talc masterbatch (trade name “MO-60” manufactured by Takehara Chemical Co., Ltd.), PS / talc (mass by mass) Ratio) = 40/60) 2.2% by mass. The obtained mixture was supplied to a hopper of a tandem extruder (caliber 65 mm-90 mm) having first and second two extruders, and melted and kneaded in the first extruder, butane (isobutane) as a blowing agent. / Normal butane (mass ratio) = 30/70) was pressed into 1.2 parts by mass per 100 parts by mass of the polystyrene resin. Further melt-kneaded product was melt-kneaded was continuously fed from the first extruder to the second extruder, a resin temperature t ₁ of the second extruder was cooled to 166 ° C. suitable for foaming, connected to the second end of the extruder It was extruded from an annular mold having a diameter of 124 mm. Die tip temperature _{t 2} was 120 ° C.. The extruded cylindrical foam is placed along the outer peripheral surface of a cooling mandrel having a plug diameter of 403 mm and a length of 500 mm, and the cylindrical foam is cut by a cutter provided on the left and right sides of the cooling mandrel. Sheet). The obtained foamed sheet (primary sheet) has a thickness of 1.2 mm, an overall density d3 of 0.112 g / cm ³ , a surface layer density d4 of 0.115 g / cm ³ , and a ratio (d4 / d3) of 1.03, The open cell rate was 5.0% by volume.
A foamed sheet (primary sheet) under the conditions of a take-up speed of 13.5 m / min so as to continuously pass through a tunnel-type steam foaming tank having an overall length of 11 m, an internal temperature of 113 ° C., and a steam pressure of 0.016 MPa illustrated in FIG. ) Was transported. In the steam foaming tank, the foamed sheet was heated with 100 ° C. steam to be foamed (secondary foaming). Then, it was cooled by passing between cooling rolls having a diameter of 300 mm and a surface temperature of 35 ° C., and cut into a width of 620 mm and a length of 1000 mm to obtain a flat foamed plate having a thickness of 1.85 mm.

[Examples 2 to 5]
The raw material composition, resin temperature t ₁ , die tip temperature t ₂ , die diameter, and cooling mandrel plug diameter were changed as shown in Table 1, and the conditions of the steam foaming process were changed as shown in Table 2. Obtained a foamed plate in the same manner as in Example 1.

[Example 6]
A foamed plate was obtained in the same manner as in Example 1 except that the conditions were changed as follows.
The raw material composition, resin temperature t ₁ , die tip temperature t ₂ , die diameter, and cooling mandrel plug diameter were changed as shown in Table 1. The conditions of the steam foaming process were changed as shown in Table 2. Furthermore, as illustrated in FIG. 2, kraft paper (thickness 0.1 mm) coated with a hot melt adhesive (trade name “Hirodyne 7558, manufactured by Yasuhara Chemical Co., Ltd.) on both surfaces of the foamed plate coming out of the steam foaming tank. The hot melt adhesive layer was laminated so as to be on the foam plate side, and the temperature of the bonding hot roll was set to 100 ° C.

[Comparative Examples 1-4]
The raw material composition, resin temperature t ₁ , die tip temperature t ₂ , die diameter, and cooling mandrel plug diameter were changed as shown in Table 1, and the conditions of the steam foaming process were changed as shown in Table 2. Obtained a foamed plate in the same manner as in Example 1.

Each measurement result of the foamed sheet (primary sheet) in each example is shown in Table 1, and each measurement result and evaluation result of the foamed plate are shown in Table 2.
In addition, the compounding quantity of the foaming agent in Table 1 shows the quantity per 100 mass parts of polystyrene resins.

As shown in Table 2, the foamed plates of Examples 1 to 6 in which the thickness, the ratio (d2 / d1), and the open cell ratio all satisfy the conditions of the present invention have good appearance and suppress dimensional changes after production. It was excellent in dimensional stability, had a small surface hardness, was flexible, and had buffering properties.
On the other hand, the foamed plate of Comparative Example 1 having an open cell ratio of more than 30% by volume and a ratio (d2 / d1) of less than 0.8 has a non-uniform appearance on the surface and poor appearance, and the dimensions change after production. The dimensional stability was inferior.
The foamed plate of Comparative Example 2 having an open cell ratio of more than 30% by volume also had a poor appearance, and the dimensions changed after production, resulting in poor dimensional stability.
The foamed plates of Comparative Examples 3 and 4 having an open cell ratio of less than 9% by volume and a ratio (d2 / d1) exceeding 1.8 have good appearance and excellent dimensional stability, but have too high surface hardness. And the flexibility was poor.

  The foamed plate of the present invention can be suitably used for various applications such as cushioning materials, toys such as model airplanes, POP display substrates, and the like.

DESCRIPTION OF SYMBOLS 1 Foam sheet 2 Foam board 3 Paper 4 Laminated body 10 Foam sheet roll 12 Guide roll 14 Steam foaming tank 16 Cooling roll 18 Cutting machine 20 Paper roll 22 Bonding hot roll

Claims (4)

The thickness is 1.0 to 10 mm,
The ratio (d2 / d1) of the surface layer density d2 from the surface to the depth of 0.2 mm with respect to the total density d1 is 0.8 to 1.8,
A polystyrene-based resin foam board having an open cell ratio of 9 to 30% by volume.   The polystyrene-based resin foamed plate according to claim 1, wherein the elastic modulus is 10 to 30 MPa when a three-point press bending test is performed in accordance with JIS K7171-2008. A method for producing a polystyrene-based resin foam board according to claim 1 or 2,
Having a step of heating and foaming a polystyrene resin foam sheet with steam to obtain a polystyrene resin foam plate,
The polystyrene-based resin foam sheet has a thickness of 0.5 to 5.0 mm, and a ratio (d4 / d3) of a surface layer density d4 from the surface to a depth of 0.2 mm with respect to the overall density d3 is 1.0 to 1. And a method for producing a polystyrene-based resin foamed plate having an open cell ratio of 5 to 26% by volume.   The manufacturing method of the polystyrene-type resin foam board of Claim 3 whose said vapor | steam is water vapor | steam.

Images