JP2004269611A - Production method for styrenic resin foam sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of producing a styrenic resin foam sheet which maintains a state suitable for molding for a long time, has fine cells, and is excellent in mechanical strength and external appearance. <P>SOLUTION: In this production method, a styrenic resin and a blowing agent are fed to an extruder and extrusion-foamed through a circular die into a tubular shape; thus formed tubular foam is cut and unfolded to give the objective foam sheet. The blowing agent is composed of 80-98 wt.% butane and 2-20 wt.% carbon dioxide, the butane being composed of 55-100 wt.% isobutane and 0-45 wt.% n-butane. The ratio (S<SB>1</SB>/S<SB>0</SB>) of the sectional area (S<SB>1</SB>) at a part in the molten resin channel and distant by 5 mm from the outlet of the circular die in the direction reverse to the resin flow direction to the outlet area (S<SB>O</SB>) in the molten resin channel of the circular die is 1.25-2.25. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００８８】
【発明の効果】
本発明のスチレン系樹脂発泡シートの製造方法は、スチレン系樹脂及び発泡剤を押出機に供給して溶融、混練した後に押出機の先端に取り付けたサーキュラ金型から円筒状に押出発泡し、この円筒状発泡体を切断、展開してシート状にするスチレン系樹脂発泡シートの製造方法において、上記発泡剤は、ブタン８０〜９８重量％及び二酸化炭素２〜２０重量％からなり且つ上記ブタンがイソブタン５５〜１００重量％及びノルマルブタン０〜４５重量％からなると共に、上記サーキュラ金型の溶融樹脂流路における出口面積（Ｓ_０ ）と、サーキュラ金型の溶融樹脂流路における出口から樹脂の流通方向の反対方向に５ｍｍ存した部分の断面積（Ｓ_１ ）との比（Ｓ_１ ／Ｓ_０ ）が１．２５〜２．２５であることを特徴とし、ブタンと二酸化炭素とが所定割合で混合されて互いの欠点を補完しつつ長所を顕在化させていることから押出発泡安定性に優れており、得られたスチレン系樹脂発泡シートは、微細な気泡を有して機械的強度に優れ且つ成形に適した発泡剤量となるまでの熟成期間が短い上に成形に適した発泡剤量を長期間に亘って持続して成形ライフが長いといった優れた効果を奏するものである。
【図面の簡単な説明】
【図１】サーキュラ金型を示した縦断面図である。
【図２】サーキュラ金型の溶融樹脂流路の出口形状を示した正面図である。
【図３】サーキュラ金型の溶融樹脂流路における出口から樹脂の流通方向の反対方向に５ｍｍ存した部分を示した正面図である。
【符号の説明】
１ サーキュラ金型
２ 外側口金
３ 内側口金
４ 溶融樹脂流路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a method for producing a styrene-based resin foam sheet capable of stably producing a styrene-based resin foam sheet having fine bubbles and excellent mechanical strength while maintaining a state suitable for molding for a long period of time. About the method.
[0002]
[Prior art]
Styrene-based resin foam sheets are used in large quantities in food containers and the like because they have excellent thermoformability, appearance and cushioning properties, and are light in weight and low in cost. This foamed styrene resin sheet is manufactured by supplying a styrene resin and a foaming agent to an extruder, melting, kneading, and extruding and foaming.
[0003]
The styrene-based resin foam sheet contains a foaming agent, but when the foaming agent amount is large, there is a problem that a molded article obtained has a large surface roughness due to a large influence of plasticization by the foaming agent. On the other hand, when the amount of the foaming agent is small, secondary foaming (secondary foaming property) at the time of molding is insufficient, and a molded article having a desired shape cannot be obtained.
[0004]
Therefore, after the styrene resin foam sheet is extruded from the extruder, the foaming agent in the styrene resin foam sheet is dissipated by leaving (aging) for a predetermined period, and the amount of the foaming agent in the styrene resin foam sheet is reduced. The amount is adjusted to be suitable for
[0005]
Patent Document 1 discloses a method for producing a styrene-based resin foam sheet in which the aging period is short and the amount of the foaming agent suitable for molding can be maintained over a long period of time. A mixture comprising 70% by weight or less of isobutane, 15% by weight or more and 30% by weight or less of normal butane, 0.5% by weight or more and less than 50% by weight of propane, and 0% by weight or more and 5% by weight or less of another physical blowing agent Used.
[0006]
However, since propane has a high foaming speed and easily causes streaks on the surface of the internal foam and the styrene resin foam sheet, it is possible to stably produce a styrene resin foam sheet having excellent appearance and mechanical strength. There was a problem that it could not be done.
[0007]
[Patent Document 1]
JP 2001-105471 A (Claims)
[0008]
[Problems to be solved by the invention]
The present invention is capable of maintaining a state suitable for molding for a long period of time, and stably producing a styrene-based resin foam sheet having fine bubbles, excellent mechanical strength, and excellent appearance. Provided is a method for producing a foamed styrene resin sheet.
[0009]
[Means to solve the problem]
In the method for producing a styrene-based resin foam sheet of the present invention, a styrene-based resin and a foaming agent are supplied to an extruder, melted, kneaded, and then extruded into a cylindrical shape from a circular mold attached to the tip of the extruder. In the method for producing a styrenic resin foam sheet obtained by cutting and expanding a cylindrical foam to form a sheet, the blowing agent comprises 80 to 98% by weight of butane and 2 to 20% by weight of carbon dioxide, and the butane is isobutane. 55 to 100% by weight and 0 to 45% by weight of normal butane, and the outlet area (S₀  ) And the cross-sectional area of a portion 5 mm from the outlet in the molten resin flow path of the circular mold in the direction opposite to the resin flow direction (S₁  ) And the ratio (S₁  / S₀  ) Is 1.25 to 2.25.
[0010]
The styrene resin is not particularly limited, and examples thereof include styrene homopolymers such as polystyrene and poly-p-methylstyrene, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, and styrene-butadiene copolymer. Examples include polymers, styrene-acrylonitrile-butadiene copolymers, styrene-based copolymers such as styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, and mixtures of polystyrene and polyphenylene oxide.
[0011]
When the melt mass flow rate of the styrene-based resin is low, the extrusion foamability of the styrene-based resin or the elongation of the foamed styrene-based resin sheet during molding may be reduced. , 1.2 g / 10 min or more, more preferably 1.25 g / 10 min or more.
[0012]
Further, if the melt mass flow rate of the styrene resin is high, the foaming agent contains a highly secondary foamable isobutane, and the foamed styrene resin sheet may draw down or undulate during molding. , 2.5 g / 10 min or less, more preferably 1.9 g / 10 min or less, particularly preferably 1.8 g / 10 min or less. In addition, the melt mass flow rate of the styrene-based resin refers to a value measured according to JIS K7210.
[0013]
Further, in the method for producing a styrene resin foam sheet of the present invention, the foaming agent comprises 80 to 98% by weight of butane and 2 to 20% by weight of carbon dioxide, and the butane is 55 to 100% by weight of isobutane and 0 to 0% of normal butane. What consists of 45 weight% is used.
[0014]
That is, the present invention is characterized in that a blowing agent obtained by mixing butane, in particular, isobutane and carbon dioxide is used. This is because isobutane has a low rate of dissipation from the styrene-based resin, and therefore remains in the styrene-based resin foam sheet for a long period of time. While the rate of decrease can be reduced and the amount of the foaming agent in the styrene resin foam sheet can be maintained in a state suitable for molding for a long period of time, the aging period of the styrene resin foam sheet becomes longer. Problems arise. Further, when normal butane is used in a large amount with respect to isobutane, there arises a problem that bubbles of the foamed styrene resin sheet become large.
[0015]
On the other hand, when carbon dioxide has a very low boiling point and is used in a large amount as a foaming agent, internal foaming tends to occur during extrusion foaming, and the appearance of the foamed styrene-based resin sheet tends to deteriorate.
[0016]
However, carbon dioxide can maintain the amount of blowing agent in the styrene-based resin foam sheet in a state suitable for molding over a long period of time by adding a small amount of isobutane to butane as a main component. The cells of the styrene resin foam sheet can be miniaturized.
[0017]
Moreover, carbon dioxide has a high rate of dissipation to the styrene-based resin, and is quickly dissipated from the styrene-based resin foam sheet after extrusion foaming, so that the maturation period of the styrene-based resin foam sheet can be shortened.
[0018]
In addition, carbon dioxide is rapidly cooled and solidified due to a large heat loss when the molten styrene-based resin extruded from the mold foams, and is cooled during the cooling of the styrene-based resin foam sheet. Is strongly stretched to improve the strength of the cell membrane, thereby obtaining a styrene-based resin foam sheet having excellent mechanical strength.
[0019]
Therefore, in the present invention, a foaming agent obtained by mixing butane, particularly isobutane, and carbon dioxide at a predetermined ratio is used, and the advantages of both are exhibited synergistically while complementing each other's drawbacks, which is suitable for molding. The styrene-based resin foam sheet having fine bubbles and excellent mechanical strength can be stably produced while maintaining the state over a long period of time.
[0020]
That is, the obtained styrene-based resin foam sheet has bubbles formed of a cell membrane which is fine and has excellent strength by the action of carbon dioxide, and has excellent mechanical strength.
[0021]
Moreover, the obtained styrene-based resin foam sheet can quickly dissipate carbon dioxide and reduce the amount of the foaming agent to an amount suitable for molding in a short period of time, that is, the aging period can be shortened. The amount of the foaming agent suitable for this molding can be maintained over a long period of time by the action of butane, particularly isobutane, which dissipates slowly from the styrene-based resin, so that the styrene-based resin foam sheet is suitable for molding. (Molding life) can be extended.
[0022]
For these reasons, the content of butane in the foaming agent is limited to 80 to 98% by weight, preferably 82 to 97% by weight, and more preferably 85 to 96% by weight. For the same reason, the content of carbon dioxide in the blowing agent is limited to 2 to 20% by weight, preferably 3 to 18% by weight, and more preferably 4 to 15% by weight.
[0023]
As the butane, isobutane alone or a mixture of isobutane and normal butane is used, and normal butane may be used as needed within a predetermined ratio.
[0024]
That is, if the content of isobutane in butane is small, the molding life of the styrene-based resin foam sheet is shortened, so that the content is limited to 55 to 100% by weight. Since a streak may be generated on the sheet surface, the content is preferably 60 to 99% by weight, more preferably 65 to 98% by weight. For the same reason, the content of normal butane in butane is limited to 0 to 45% by weight, preferably 1 to 40% by weight, and more preferably 2 to 35% by weight.
[0025]
Further, when the weight ratio of isobutane to carbon dioxide (isobutane / carbon dioxide) in the above foaming agent is low, the plasticizing effect during extrusion foaming of the styrene resin is reduced, and the open cell ratio of the styrene resin foam sheet is reduced. May increase and the mechanical strength may decrease, or the secondary foamability of the styrene resin foam sheet may decrease. Since the aging period of the foam sheet may be long, 3.3 to 24 is preferable, 3.5 to 22 is more preferable, and 3.7 to 20 is particularly preferable.
[0026]
Incidentally, the foaming agent, the extrudable foaming of the styrene resin, the aging period of the styrene resin foam sheet and within a range that does not impair the molding life, propane, isopentane, normal pentane, hydrocarbons such as neopentane, dimethyl ether and the like. An ether compound may be added.
[0027]
Further, since the foaming agent is flammable, it is preferable to add an antistatic agent to the styrene resin. As such an antistatic agent, an ester of a polyhydric alcohol and a higher fatty acid, and a higher fatty acid alcoholic ester having one or more hydroxyl groups in a free state in the molecule is preferable.
[0028]
Examples of the polyhydric alcohol include glycerin, pentaerythritol, sorbit, sorbitan, mannitol, mannitane, dipentaerythritol, diglycerin and the like.
[0029]
Examples of the higher fatty acids include, for example, monovalent of saturated or unsaturated and having 10 to 30 carbon atoms such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid and linoleic acid. Higher fatty acids, or bovine fatty acids, bran oil fatty acids, coconut oil fatty acids, and the like in which these higher fatty acids are mixed are exemplified.
[0030]
Examples of the higher fatty acid alcoholic ester include, for example, lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, pentaerythritol monocaprate, pentaerythritol monooleate, pentaerythritol monolaurate, dipentaerythritol diglyceride Stearate, sorbitan monooleate, sorbitan sesqui bran oil fatty acid ester, sorbitan monopalmitate, sorbitan monolaurate, sorbitan monostearate, mannitan monooleate, mannitan monolaurate, etc., and stearic acid monoglyceride is preferred. .
[0031]
Further, if the amount of the antistatic agent is small, the effect of the addition is not exhibited, and if the amount is large, the appearance of the foamed styrene resin sheet may be deteriorated or warpage or shrinkage may occur. The amount is preferably 0.01 to 1.0 part by weight, more preferably 0.02 to 0.5 part by weight, and particularly preferably 0.03 to 0.3 part by weight based on 100 parts by weight of the resin.
[0032]
In addition, the styrene-based resin may be an inorganic powder such as talc, magnesium carbonate, pearlite, calcium carbonate, clay, vermiculite, or the like, as long as the physical properties and production of the styrene-based resin foam sheet are not hindered. A bubble regulator such as dicarbonamide, trihydrazinotriazine, benzenesulfonyl semicarbazide, polytetrafluoroethylene resin powder, or organic powder such as citric acid, a pigment, a deterioration inhibitor, a flame retardant, etc. may be added.
[0033]
Next, a specific procedure for producing a styrene resin foam sheet using the styrene resin and the foaming agent will be described. First, the extruder used in the method for producing a styrene-based resin foam sheet of the present invention is not particularly limited as long as it is a conventionally used extruder, for example, a single-screw extruder, a twin-screw extruder, A tandem type extruder in which a plurality of extruders are connected is exemplified, and a tandem type extruder is preferable.
[0034]
Then, the styrene resin is supplied to the extruder, melted and kneaded, and the foaming agent is pressed into the molten styrene resin in the extruder by using an injection pump.
[0035]
At this time, rather than pre-mixing butane and carbon dioxide and then press-fitting into the extruder, fine-tune the press-fitting amount of butane and carbon dioxide separately while checking the extrusion foaming state of the styrene resin foam sheet. Therefore, it is preferable to press-fit butane and carbon dioxide into the extruder at different timings.
[0036]
Then, when butane and carbon dioxide are injected into the extruder at different timings, it is preferable that carbon dioxide is injected into the extruder after butane is injected into the extruder.
[0037]
This is because the melt viscosity of the styrene-based resin can be reduced by injecting butane into the styrene-based resin in a molten state, and by injecting carbon dioxide into the styrene-based resin in a state where the melt viscosity is reduced. This is because carbon dioxide can be more uniformly dispersed in the styrene resin.
[0038]
Further, in order to improve the dispersibility of the blowing agent in the styrene-based resin, the styrene-based resin in a molten state heated to a temperature equal to or higher than the critical temperature of the blowing agent and applied with a pressure equal to or higher than the critical pressure of the blowing agent. Preferably, the blowing agent is press-fitted. Specifically, a styrene-based resin in a molten state heated to a temperature higher than the critical temperature of the blowing agent in the extruder and applied with a pressure higher than the critical pressure of the blowing agent Among them, there is a method of injecting a foaming agent at a pressure higher than its critical pressure.
[0039]
Specifically, in the case of isobutane, since the critical temperature of isobutane is 135 ° C. and the critical pressure is 3.5 MPa, it is heated to a temperature of 135 ° C. or more and melted under a pressure of 3.5 MPa or more. Isobutane is preferably injected into the styrene-based resin in a state, more preferably 185 is injected into the molten styrene-based resin heated to a temperature of 160 ° C. or more and a pressure of 5 MPa or more is applied. It is particularly preferable to press-fit isobutane into a styrene-based resin in a molten state heated to a temperature of not less than 0 ° C. and to which a pressure of not less than 7 MPa is applied.
[0040]
In the case of normal butane, since the critical temperature of normal butane is 152 ° C. and the critical pressure is 3.8 MPa, the molten state is heated to a temperature of 152 ° C. or more and a pressure of 3.8 MPa or more is applied. Normal butane is preferably pressed into the styrene-based resin of, more preferably normal butane is pressed into a molten styrene-based resin heated to a temperature of 160 ° C. or more and a pressure of 5 MPa or more is applied, It is particularly preferable to inject normal butane into a styrene-based resin in a molten state heated to a temperature of 185 ° C. or higher and a pressure of 7 MPa or higher.
[0041]
Further, in the case of carbon dioxide, since the critical temperature of carbon dioxide is 31 ° C. and the critical pressure is 7.4 MPa, styrene in a molten state heated to a temperature of 120 ° C. or more and applied with a pressure of 9 MPa or more is applied. It is preferable to inject carbon dioxide into the system-based resin, and it is more preferable to press-inject carbon dioxide into a molten styrene-based resin heated to a temperature of 140 ° C. or more and a pressure of 9.5 MPa or more is applied, It is particularly preferable to inject carbon dioxide into a molten styrene resin heated to a temperature of 160 ° C. or higher and a pressure of 10 MPa or higher.
[0042]
When a tandem extruder is used as the extruder, the foaming agent is press-fitted in the first extruder, and the dispersed styrene resin in the molten state is mixed with the first extruder and the second extruder. Is continuously supplied to the second-stage extruder through a connecting pipe connecting the styrene to the highest critical temperature of butane and carbon dioxide constituting the blowing agent in the connecting pipe. By heating the styrene-based resin and applying a pressure equal to or higher than the highest critical pressure of butane and carbon dioxide constituting the blowing agent to the styrene-based resin, the blowing agent is further converted into the styrene-based resin in a critical state. A large amount and uniform dissolution can be achieved, so that the cells of the obtained styrene resin foam sheet can be made finer and the mechanical strength can be improved.
[0043]
Further, the first-stage extruder aims to sufficiently disperse the foaming agent in the styrene resin, and such an extruder includes a twin-screw extruder excellent in mixing and kneading properties, and a foaming agent. A single screw extruder provided with a screw having a highly kneaded portion such as a dalmage or a pin near the press-fitting portion is preferred.
[0044]
In addition, the main purpose of the second-stage extruder is to cool the styrene-based resin to an appropriate foaming temperature. For example, an extruder having a screw capable of uniformly cooling a styrene-based resin containing the same to an appropriate foaming temperature, such as a screw having a dalmage portion or a screw in which a part of a screw flight is cut off, is preferable.
[0045]
When the amount of the foaming agent injected into the molten styrene-based resin is small, the styrene-based resin may not foam when the amount is small, and may be broken when the amount is large, so 100 parts by weight of the styrene-based resin. Is preferably 0.5 to 6 parts by weight, more preferably 1 to 5.5 parts by weight, and particularly preferably 1.5 to 5 parts by weight.
[0046]
The styrene resin melted and kneaded in the extruder and having the foaming agent dispersed therein is adjusted to an appropriate foaming temperature, extruded into a cylindrical shape from a circular mold attached to the extruder, and foamed. The foamed foam is supplied to a cooling mandrel and continuously cooled, and then the tubular foam is continuously cut and developed in an extrusion direction at an arbitrary portion to obtain a long styrene resin foam sheet. be able to.
[0047]
Here, in the present invention, a circular mold is used as an exit area (S₀  ) And the cross-sectional area of a portion 5 mm from the outlet in the molten resin flow path of the circular mold in the direction opposite to the resin flow direction (S₁  ) And the ratio (S₁/ S₀  ) Is 1.25 to 2.25.
[0048]
As shown in FIG. 1, the circular mold 1 has an outer base 2 that penetrates in the front-rear direction and has a space of a perfect circular cross section whose front end is gradually enlarged in diameter, and a space inside the outer base 2. And an inner base 3 having a perfect circular cross section whose front end is gradually enlarged in diameter, and penetrates in the front-rear direction between the facing surfaces of the outer base 2 and the inner base 3 and has a front end gradually. A molten resin flow path 4 having an annular cross section and having an enlarged diameter is formed.
[0049]
Then, the outlet area (S) of the circular mold 1 in the molten resin flow path 4 is set.₀  ) Means those specified in the following manner. That is, a point on the outer peripheral surface 31 of the inner die 3 which is closest to an arbitrary point A on the ring-shaped front edge 21a on the inner wall surface 21 of the space of the outer die 2 of the circular die 1 is defined as a point B, The point B on the outer peripheral surface 31 of the inner base 3 is continuously specified while the point A on the ring-shaped front end edge 21a is continuously moved in the circumferential direction. The circle formed on the surface 31 is defined as a virtual first circle 31a.
[0050]
The portion formed between the ring-shaped front edge 21a of the outer die 2 of the circular mold 1 thus obtained and the imaginary first circle 31a of the inner die 3 opposed thereto is defined as an annular outlet E. The area of the annular outlet E is determined by the area of the outlet in the molten resin flow path 4 of the circular mold 1 (S₀  (See Fig. 2)
[0051]
Then, the outlet area (S) of the circular mold 1 in the molten resin flow path 4 is set.₀  ) Can be obtained in the following manner. That is, the distance between an arbitrary point A on the ring-shaped front edge 21a on the inner wall surface 21 of the space of the outer base 2 and a point B on the virtual first circle 31a of the inner base 3 corresponding to this point A is represented by t.₀  And the distance between the midpoint C between the points A and B and the axis D of the inner base 3 is represented by r.₀  And can be calculated by the following equation 1. S₀  = (R₀  + T₀  / 2)²  π- (r₀  -T₀  / 2)²  π
= 2πr₀  t₀  ... Equation 1
[0052]
If the distance between the ring-shaped front edge 21a of the outer base 2 and the imaginary first circle 31a of the inner base 3 is not constant, the point A is arbitrarily set on the ring-shaped front edge 21a.₁  ~ A₈Are determined for each phase difference of 45 ° in the circumferential direction, and each point A₁  ~ A₈  Point B corresponding to₁  ~ B₈  Respectively, and the point A₁  ~ A₈  And the corresponding point B₁  ~ B₈  Distance t₁  ~ T₈  The average of t₀  And each point A₁  ~ A₈  And the corresponding point B₁  ~ B₈  Halfway point C with₁  ~ C₈  And the intermediate point C₁  ~ C₈  And the distance r between the inner base 3 and the axis D₁  ~ R₈  The average of₀  And
[0053]
Furthermore, the cross-sectional area (S₁  ) Means those specified in the following manner.
[0054]
That is, the ring-shaped front edge 21a of the outer die 2 of the circular mold 1 is parallel to the axial center D direction of the inner die 3 at the rear from the ring-shaped front edge 21a along the inner wall surface 21 of the space of the outer die 2 by 5 mm. The virtual second circle 21b is specified at the moved position, and the virtual first circle 31a of the inner base 3 is moved from the virtual first circle 31a along the outer peripheral surface 31 of the inner base 2 to the axis of the inner base 3 at the rear. The virtual third circle 31b is specified at a position translated by 5 mm in the direction of the core D.
[0055]
The area of the portion formed between the imaginary second circle 21b thus obtained and the imaginary third circle 31b opposed to the imaginary second circle 21b is defined as the area between the outlet in the molten resin flow path of the circular mold and the flow direction of the resin. The cross-sectional area (S₁  ) (See FIG. 3).
[0056]
The cross-sectional area (S₁  ) Can be obtained in the following manner. That is, a distance between an arbitrary point F on the virtual second circle 21b of the outer base 2 and a point G on the virtual third circle 31b closest to the point F is represented by T.₀  And the distance between the midpoint H between the point F and the point G and the axis D of the inner base 3 is represented by R₀  And can be calculated by the following equation 2.
S₁  = (R₀  + T₀  / 2)²  π- (R₀  −T₀  / 2)²  π
= 2πR₀  T₀  ... Equation 2
[0057]
When the distance between the imaginary second circle 21b of the outer base 2 and the imaginary third circle 31b of the inner base 3 is not constant, an arbitrary point F is set on the imaginary second circle 21b.₁  ~ F₈  Is determined for each phase difference of 45 ° in the circumferential direction, and each point F₁  ~ F₈  G on the virtual third circle 31b closest to₁  ~ G₈  Respectively, and the point F₁  ~ F₈  And the corresponding point G₁  ~ G₈  Distance T with₁  ~ T₈  The average of T₀  And each point F₁  ~ F₈  And the corresponding point G₁  ~ G₈  Halfway point H with₁  ~ H₈  And the intermediate point H₁  ~ H₈  And the distance R between the inner cap 3 and the axis D₁  ~ R₈  The average of R₀  And
[0058]
The outlet area (S) in the molten resin flow path of the circular mold obtained as described above₀  ) And the cross-sectional area of a portion 5 mm from the outlet in the molten resin flow path of the circular mold in the direction opposite to the resin flow direction (S₁  ) And the ratio (S₁  / S₀  ) Indicates how much the throttle is narrowed from the portion 5 mm behind the annular outlet E of the circular mold 1 to the annular outlet E. The greater the value, the greater the degree of narrowing. Is shown.
[0059]
Then, the above (S₁  / S₀  ) Is small, internal foaming occurs in the circular mold 1 and the appearance of the obtained styrene resin foam sheet is deteriorated, and if it is large, melt fracture is generated and the appearance of the obtained styrene resin foam sheet is Is reduced, the ratio is limited to 1.25 to 2.25, preferably 1.4 to 2.1, and more preferably 1.5 to 2.0.
[0060]
Also, the exit area of the circular mold 1 (S₀  ) And the shear rate at the circular exit E of the circular mold 1 (exit area (S₀  ) / Shear rate) is low, melt fracture may occur, and the appearance of the resulting styrene resin foam sheet may be degraded. On the other hand, if it is high, the foam may be internally foamed and the appearance of the resulting styrene resin foam sheet may be reduced. 0.02 to 0.11 mm²  -Sec is preferable.
[0061]
The shear rate at the circular outlet E of the circular mold 1 is calculated based on the following double pipe calculation formula.
Shear rate (sec^-1) = 6Q / [π (L₂  ²  -L₁  ²  ) (L₂  -L₁  )]
Here, Q is the volumetric extrusion amount of the styrene resin (cm³  / Sec) (where Q is calculated from the mass extrusion rate (g / sec), the density of the styrene resin is 0.8 g / cm).³And L₁  (Cm) is (r₀  -T₀  / 2) and L₂  (Cm) is (r₀  + T₀  / 2).
[0062]
Furthermore, by cooling the cylindrical foam by blowing cooling air to the inner and outer peripheral surfaces of the cylindrical foam discharged from the circular mold, if a skin layer is formed on the inner and outer surfaces of the cylindrical foam, A styrene-based resin foam sheet having excellent appearance can be produced, which is preferable.
[0063]
The styrene resin foam sheet usually has a thickness of 0.7 to 3.5 mm and a basis weight of 70 to 400 g / m.²  , Density is 0.05-0.35g / cm³  Is preferably adjusted to, but is not limited to, these conditions.
[0064]
Here, when the appropriate foaming temperature is low, the dispersibility of the foaming agent in the styrene-based resin decreases, and the viscosity of the molten resin containing the foaming agent becomes too high, whereby a good styrene-based resin foam sheet is obtained. In some cases, if it is too high, the foaming speed becomes too fast, and a good styrene-based resin foam sheet may not be obtained. Since the dispersibility of the foaming agent can be improved by this, 135 to 168 ° C is preferable, 140 to 166 ° C is more preferable, and 145 to 164 ° C is particularly preferable.
[0065]
Then, the long styrene-based resin foam sheet manufactured as described above is once wound into a roll and aged for a predetermined period of time to dissipate the foaming agent in the styrene-based resin foam sheet, After the amount of the foaming agent in the styrene-based resin foam sheet is adjusted to an amount suitable for thermoforming, the sheet is thermoformed into a desired shape such as a container.
[0066]
If the amount of the foaming agent in the styrene-based resin foam sheet during the thermoforming is small, secondary foam is insufficient and a molded article having a desired thickness cannot be obtained, or the styrene-based resin foam sheet is formed into a desired shape. If it is too large, the plasticizing effect of the styrenic resin by the foaming agent is too large, and the surface of the styrenic resin foam sheet surface is roughened during thermoforming and the appearance of the molded product deteriorates. 2.0 to 3.4% by weight is preferred, and 2.1 to 3.2% by weight, because the styrene-based resin foam sheet may draw down and undulate during thermoforming to cause molding failure. % By weight is more preferable, and 2.2 to 3.0% by weight is particularly preferable.
[0067]
【Example】
(Example 1)
100 parts by weight of styrene resin (trade name "G9305" manufactured by A & M Styrene Co., Ltd., melt mass flow rate: 1.5 g / 10 minutes), 1.0 part by weight of talc, and a master batch of stearic acid monoglyceride (styrene resin / stearic acid monoglyceride ( Monoglyceride content: 95% by weight or more) (weight ratio) = 4) A resin mixture obtained by uniformly mixing 0.5 parts by weight with a tumbler in advance was mixed with a single-stage extruder having a diameter of 50 mm in the first stage and a second stage. A single-screw extruder having a diameter of 65 mm was connected to a first-stage extruder of a tandem type extruder which was connected via a connection pipe.
[0068]
Then, the styrene resin is melted and kneaded at 170 to 220 ° C. in the first stage extruder, and 4 parts by weight of butane (isobutane 95% by weight, normal butane 5% by weight) is passed through one inlet of the first stage extruder. Immediately after being injected at a pressure of 15 MPa or more into a molten styrenic resin heated to 220 ° C. and to which a pressure of 15 MPa was applied, immediately after passing carbon dioxide 0.2 through another injection port in the first extruder. Parts by weight of a styrene-based resin in a molten state heated to 220 ° C. and applied with a pressure of 15 MPa at a pressure of 15 MPa or more, and carbon dioxide and butane are introduced into the styrene resin by a screw equipped with a pin. Dispersed uniformly.
[0069]
Thereafter, the molten styrene resin was continuously supplied from the first extruder to the second extruder via a connecting pipe. The temperature of the styrene resin in the connection pipe was 190 ° C., and the pressure applied to the styrene resin was 13.0 MPa.
[0070]
Then, the styrene resin in a molten state in the second-stage extruder was attached to the tip of the second-stage extruder after the screw flight was cooled to a resin temperature of 160 ° C. by a partially cut screw. It was extruded and foamed into a cylindrical shape from the circular mold shown in FIG. The resin temperature was measured by inserting a breaker plate between the second-stage extruder and the circular mold, and inserting a thermocouple at the center of the breaker plate.
[0071]
Here, the circular mold is shown in FIGS.₀  (Distance between point A and point B) is 0.56 mm, r₀  Is 29.77mm, T₀  (Distance between point F and point G) is 1.00 mm, R₀  Is 27.09 mm, S₀  Is 105mm²  , S₁  Is 170mm², S₁  / S₀  Is 1.62, and the shear rate at the annular outlet E of the circular mold 1 is 1065.1 sec.^-1, The exit area of the circular mold 1 (S₀  ) And the shear rate at the circular exit E of the circular mold 1 (exit area (S₀  ) / Shear rate) is 0.0986 mm²  -It was sec. The mass extrusion rate was 8.33 g / sec, L₁  Is 2.949 cm and L₂  Was 3.005 cm.
[0072]
Then, air at 30 ° C. is blown onto each of the inner and outer peripheral surfaces of the cylindrical foam to cool the inner and outer peripheral surfaces of the cylindrical foam, and then continuously supplied to a mandrel cooled by cooling water at 30 ° C. After cooling, the foamed sheet for molding styrene resin is continuously manufactured by continuously cutting and expanding the cylindrical foam in any direction in the extrusion direction, and this long styrene-based resin is formed. The foam sheet was wound into a roll by a winder. The styrene resin foam sheet has a basis weight of 200 g / m2.²The thickness was 2.10 mm, and the bubbles were fine and the appearance was excellent.
[0073]
(Example 2)
A styrene-based resin foam sheet was obtained in the same manner as in Example 1 except that butane (70% by weight of isobutane and 30% by weight of normal butane) was used in a proportion of 3.6 parts by weight and carbon dioxide was used in an amount of 0.6 part by weight. The styrene resin foam sheet has a basis weight of 200 g / m2.²  , The thickness was 2.10 mm, the bubbles were fine, and the appearance was excellent.
[0074]
(Example 3)
As a circular mold, in FIGS.₀  (Distance between point A and point B) is 0.56 mm, r₀  Is 29.78 mm, T₀  (Distance between point F and point G) is 1.17 mm, R₀  Is 27.02 mm, S₀  Is 105mm²  , S₁  Is 199mm²  , S₁  / S₀  Is 1.90, and the shear rate at the circular outlet E of the circular mold 1 is 1064.7 sec.^-1, The exit area of the circular mold 1 (S₀  ) And the shear rate at the circular exit E of the circular mold 1 (exit area (S₀  ) / Shear rate) is 0.0986 mm²  A styrene-based resin foam sheet was obtained in the same manner as in Example 1 except that a circular mold was used. The styrene resin foam sheet has a basis weight of 200 g / m2.²  , The thickness was 2.10 mm, the bubbles were fine, and the appearance was excellent. The mass extrusion rate was 8.33 g / sec, L₁  Is 2.950 cm and L₂  Was 3.006 cm.
[0075]
(Comparative Example 1)
5.21 parts by weight of butane (95% by weight of isobutane, 5% by weight of normal butane) were press-fitted into the first stage extruder, and a styrene resin foam sheet was prepared in the same manner as in Example 1 except that carbon dioxide was not used. Got. The styrene resin foam sheet has a basis weight of 200 g / m2.²  And the thickness was 2.10 mm.
[0076]
(Comparative Example 2)
A styrene-based resin foam sheet was obtained in the same manner as in Example 1 except that butane was changed to 4.0 parts by weight (50% by weight of isobutane and 50% by weight of normal butane) and 0.2 part by weight of carbon dioxide. The styrene resin foam sheet has a basis weight of 200 g / m2.²  And the thickness was 2.10 mm.
[0077]
(Comparative Example 3)
An attempt was made to produce a foamed styrene resin sheet in the same manner as in Example 1 except that butane was used in an amount of 3.3 parts by weight (70% by weight of isobutane and 30% by weight of normal butane) and 0.9 part by weight of carbon dioxide. However, internal foaming occurred in the circular mold, and only a styrenic resin foam sheet having poor appearance was obtained. The styrene resin foam sheet has a basis weight of 200 g / m2.²  And the thickness was 2.10 mm.
[0078]
(Comparative Example 4)
As a circular mold, in FIGS.₀  (Distance between point A and point B) is 0.56 mm, r₀  Is 29.79 mm, T₀  (Distance between point F and point G) is 1.43 mm, R₀  Is 26.93 mm, S₀  Is 105mm²  , S₁  Is 242mm²  , S₁  / S₀  Is 2.30, and the shear rate at the annular outlet E of the circular mold 1 is 1064.3 sec.^-1, The exit area of the circular mold 1 (S₀  ) And the shear rate at the circular exit E of the circular mold 1 (exit area (S₀  ) / Shear rate) is 0.0987 mm²  An attempt was made to obtain a styrene-based resin foam sheet in the same manner as in Example 2 except that a circular mold was used which was a sec. No sheet was obtained. The mass extrusion rate was 8.33 g / sec, L₁  Is 2.951 cm and L₂  Was 3.007 cm.
[0079]
(Comparative Example 5)
As a circular mold, in FIGS.₀  (Distance between point A and point B) is 0.56 mm, r₀  Is 29.76 mm, T₀  (Distance between point F and point G) is 0.73 mm, R₀  Is 27.19 mm, S₀  Is 105mm²  , S₁  Is 125mm²  , S₁  / S₀  Is 1.19, and the shear rate at the annular outlet E of the circular mold 1 is 1065.4 sec.^-1, The exit area of the circular mold 1 (S₀  ) And the shear rate at the circular exit E of the circular mold 1 (exit area (S₀  ) / Shear rate) is 0.0986 mm²  An attempt was made to obtain a styrene-based resin foam sheet in the same manner as in Example 2 except that a circular mold was used which was a sec. Could not get. The mass extrusion rate was 8.33 g / sec, L₁  Is 2.948 cm, L₂  Was 3.004 cm.
[0080]
The average cell diameter, surface hardness, secondary foamability, and moldability of the styrene resin foam sheet produced as described above were measured by the following methods. The results are shown in Table 1.
[0081]
(Average bubble diameter)
The styrene-based resin foam sheet is cut at an arbitrary location in the extrusion direction and in the thickness direction along the direction orthogonal to the extrusion direction, and these cut surfaces are scanned with a scanning electron microscope (trade name “JSM-T- manufactured by JEOL Ltd.”). 300 "), and in the extrusion direction (MD direction), the direction along the surface of the styrene resin foam sheet and perpendicular to the extrusion direction (TD direction) and the thickness direction in accordance with ASTM D2842-69. The average cell diameter in the (VD direction) was calculated, and the arithmetic average of the average cell diameters in these three directions was defined as the average cell diameter.
[0082]
(surface hardness)
The styrene-based resin foam sheet was extruded and foamed, and then allowed to stand at normal temperature and normal pressure for 40 days. Then, a rectangular test piece having a length of 10 cm and a width of 500 cm was cut out. Then, the surface hardness of the foamed styrene resin sheet is determined by pressing a surface hardness of the test piece against a surface of the test piece with a rubber hardness meter (spring type hardness tester) (trade name “CS type” manufactured by Kobunshi Keiki Co., Ltd.). It was measured. The measurement points of the surface hardness of the test piece were set at intervals of 10 cm in the horizontal direction from the lateral edge at the center in the vertical direction.
[0083]
(Secondary foaming)
After the styrene resin foam sheet was extruded and foamed and allowed to stand for 40 days, a flat square test piece with a side of 10 cm was cut out from the styrene resin foam sheet.
[0084]
The test piece was left in an oven maintained at 125 ° C. for 150 seconds to heat and foam. Next, the dimensions of the foamed test piece in the vertical, horizontal and thickness directions were measured, and the secondary foamability was calculated by the following equation.
Secondary foaming property = volume of test piece after foaming / volume of test piece before foaming
[0085]
(Moldability)
From each of the styrene-based resin foam sheets left for 14 days and 40 days after extrusion foaming, a square test piece having a side of 30 cm was cut out.
[0086]
Then, each test piece is thermoformed using a thermoforming machine, and is obliquely outward in the upward direction from the four edges of the bottom surface of the horizontally long rectangular shape having a length of 10.5 cm and a width of 20.5 cm. A dish-shaped molded body having a peripheral wall extending was obtained. The corners of the obtained molded body were visually observed and judged according to the following criteria.
・ ・ ・: All the corners were formed according to the mold of the thermoforming machine.
×: One of the corners was not formed in accordance with the mold of the thermoforming machine.
[0087]
[Table 1]

[0088]
【The invention's effect】
In the method for producing a styrene-based resin foam sheet of the present invention, a styrene-based resin and a foaming agent are supplied to an extruder, melted, kneaded, and then extruded into a cylindrical shape from a circular mold attached to the tip of the extruder. In the method for producing a styrenic resin foam sheet obtained by cutting and expanding a cylindrical foam to form a sheet, the blowing agent comprises 80 to 98% by weight of butane and 2 to 20% by weight of carbon dioxide, and the butane is isobutane. 55 to 100% by weight and 0 to 45% by weight of normal butane, and the outlet area (S₀  ) And the cross-sectional area of a portion 5 mm from the outlet in the molten resin flow path of the circular mold in the direction opposite to the resin flow direction (S₁  ) And the ratio (S₁  / S₀  ) Is 1.25 to 2.25, and butane and carbon dioxide are mixed at a predetermined ratio to complement each other's drawbacks and to realize the advantages while extruding foaming stability is excellent. The obtained styrene-based resin foam sheet has fine bubbles, has excellent mechanical strength, has a short aging period until the foaming agent amount is suitable for molding, and has a foaming agent amount suitable for molding. For a long period of time and an excellent effect such as a long molding life.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a circular mold.
FIG. 2 is a front view showing an outlet shape of a molten resin flow path of a circular mold.
FIG. 3 is a front view showing a portion 5 mm from an outlet in a molten resin flow path of the circular mold in a direction opposite to a resin flowing direction.
[Explanation of symbols]
1 circular mold
2 Outer base
3 Inner base
4 molten resin channel

Claims (1)

A styrene resin and a foaming agent are supplied to an extruder, melted and kneaded, and then extruded and foamed into a cylindrical shape from a circular mold attached to the tip of the extruder.The cylindrical foam is cut and expanded to form a sheet. In the method for producing a styrenic resin foam sheet, the foaming agent comprises 80 to 98 wt% of butane and 2 to 20 wt% of carbon dioxide, and the butane is 55 to 100 wt% of isobutane and 0 to 45 wt% of normal butane. And the cross-sectional area (S ₀ ) of the exit area (S ₀ ) in the molten resin flow path of the circular mold and the portion 5 mm from the outlet in the molten resin flow path of the circular mold in the direction opposite to the resin flow direction. _A method for producing a styrene-based resin foam sheet, wherein the ratio (S ₁ / S ₀ ) to ₁ ) is from 1.25 to 2.25.

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