JP2012206462A - Method for producing plate-like foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plate-like foam restrained from warping and twisting.SOLUTION: This method for producing the plate-like foam 203 includes extrusion-foaming a polystyrene-based resin composition from a circular die 100 to form a cylindrical foam 200, then holding the foam 200 by pinch rollers 101 and thermally fusing the inner surface of the foam 200 to form the plate-like foam 203. Thin-walled parts Z thinned in wall thickness compared with the other part are formed at two parts facing with the center of the foam 200 placed in between, and the foam 200 is formed so that the thin-walled parts Z are continuous in an extruding direction. The thin-walled parts Z are thermally fused to each other to form a portion to be the width direction center part of the plate-like foam 203, thus forming the plate-like foam 203 with the thickness of the width direction center part being thinner compared with both ends in the width direction.

Description

  The present invention relates to a method for producing a plate-like foam, and more specifically, after a polystyrene resin composition is extruded and foamed from a circular die to form a cylindrical foam, the foam is formed with a pinch roll. The present invention relates to a method for producing a plate-like foam, in which a plate-like foam is formed by heat-sealing the inner surface of the foam.

Conventionally, after a polystyrene resin composition is extruded and foamed from a circular die to form a cylindrical foam, the inside of the foam is not completely cooled, and is sandwiched between pinch rolls to thermally bond the inner surfaces. A plate-like foam is formed.
Since this type of plate-like foam is lightweight and excellent in strength, it is widely used, for example, as a forming material for a mount or folding box of an exhibition panel (see Patent Document 1 below).

  This plate-like foam is required to have a smooth surface without warping or twisting, but this type of plate-like foam may be warped or twisted due to changes over time after production. In some cases, the cause has not been sufficiently determined, and no countermeasure has been established, so that it has been difficult to satisfy the demand.

JP 2009-221365 A

  This invention makes it a subject to satisfy the above requests, and makes it a subject to provide the plate-shaped foam by which curvature and the twist were suppressed.

  In order to solve the above-mentioned problems, the present inventors have intensively studied and found that a plate-like foam is a foam in which the inner surface of the foam is heat-sealed by sandwiching the tubular foam with a pinch roll. The film is stretched in the circumferential direction (width direction of the plate-like foam) and stretched in the length direction by taking-up on the downstream side of the pinch roll, and this stretching is relaxed over time and the plate It has been found that a dimensional change is caused in a foam.

  In addition, the present inventor conducted an investigation of the behavior of this dimensional change and studied the suppression measures, and it has become particularly easy to be stretched particularly at a location corresponding to the central portion in the width direction of the plate-like foam. As described above, when the thickness of the plate-like foam is manufactured uniformly, the thickness of the central portion to which this stretching is applied later is thicker than other regions and deformation such as warpage occurs, thereby completing the present invention. Has been reached.

  That is, the present invention relating to a method for producing a plate-like foam for solving the above-mentioned problems is that the polystyrene-based resin composition is extruded and foamed from a circular die to form a cylindrical foam, and then the foam is obtained. A method for producing a plate-like foam in which the inner surface of the foam is heat-sealed by pinching rolls to form a plate-like foam, and there are other two locations opposite to each other across the center of the foam. Forming a thin-walled portion thinner than the portion, forming the foam so that the thin-walled portion is continuous in the extrusion direction, and thermally bonding the thin-walled portions to each other to obtain a width of the plate-like foam By forming a portion that becomes a central portion in the direction, a plate-like foam is formed in which the thickness of the central portion in the width direction is thinner than that at both ends in the width direction.

  According to the present invention, since the plate-like foam is formed so that the thickness of the central portion in the width direction becomes thinner than both ends, the thickness of the central portion of the plate-like foam becomes thicker than other regions after manufacturing. This can be prevented, and deformation such as warpage can be prevented from occurring in the plate-like foam.

The schematic side view which shows the example of an apparatus for enforcing the manufacturing method of a plate-shaped foam. The schematic plan view which shows the example of an apparatus for enforcing the manufacturing method of a plate-shaped foam. (A) The schematic plan view which shows a punching apparatus, (b) The schematic side view of a punching apparatus. The top view which shows the evaluation sample collection location of the plate-shaped foam produced in the Example.

Embodiments according to the present invention will be described below.
First, the apparatus for enforcing the manufacturing method of the plate-shaped foam concerning this embodiment is demonstrated.
1 to 3, an arrow X indicates an extrusion direction, that is, a traveling direction of the foam.
1 and 2, reference numeral 100 denotes a circular die, and description of an apparatus such as an extruder on the upstream side of the circular die 100 is omitted.

As also shown in this figure, the plate-like foam manufacturing apparatus according to the present embodiment has a polystyrene-based resin composition extruded and foamed to form a cylindrical foam 200 (hereinafter “cylindrical foam 200”). The circular die 100 is arranged so as to form a circular discharge hole in the horizontal direction.
That is, the circular die 100 is arranged to extrude and foam the cylindrical foam 200 so as to have a cylindrical shape centered on a horizontal imaginary line passing through the center of the discharge hole.

Further, the circular die 100 has a radial width (slit width) of the discharge hole changed in the circumferential direction, and the upper and lower regions of the cylindrical foam 200 are compared with the side region. It is formed so that it can be extruded and foamed in a thinned state.
More specifically, the ejection hole in the front view is formed so that the slit widths at the upper end and the lower end in the front view are narrower than the left and right slit widths. After gradually increasing the slit width to the position of 3 and gradually decreasing the slit width to the position of 6 o'clock with the 3 o'clock position as a maximum, the slit width was similarly increased to the position of 9 o'clock to 12:00 The slit width is decreased over the position of.

That is, the circular die 100 is formed in the tubular foam 200 in the form of a strip in which the thinned region (hereinafter referred to as “thin portion”) is continuous in the extrusion direction X, and the thin portion is It is configured to be formed in two upper and lower bands.
Here, in FIG. 2, for convenience, the thin portion is clearly indicated by the hatched portion (Z), but in reality, a clear boundary is not formed between the thin portion Z and the other portions. The circular die 100 is configured to increase the thickness in an inclined manner as it is away from the central portion in the width direction of the thin-walled portion Z as described above, and can be configured to form a clear boundary with other regions. It is not what has been done.

  The plate-like foam manufacturing apparatus according to the present embodiment sandwiches the cylindrical foam 200 extruded from the circular die 100 from the top and bottom in front of the circular die 100 in the extrusion direction, and the upper half 201 of the foam 200 ( A pair of pinch rolls 101 that are heat-sealed on the inner surfaces of the lower half 202 (hereinafter also referred to as “lower sheet 202”) and a single plate-like foam 203; It further has a take-up device 104 that takes the plate-like foam 203 formed by the pinch roll 101 on the downstream side of the pinch roll 101.

The plate-shaped foam manufacturing apparatus according to this embodiment includes an air ring 103 for air-cooling the outer surface of the cylindrical foam 200 immediately after being extruded from the circular die 100, and the air ring 103. A plurality of upper and lower guide rollers 102 for guiding the air-cooled cylindrical foam 200 to the pinch roll 101 are provided.
Furthermore, the plate-like foam manufacturing apparatus according to this embodiment allows the gas inside the cylindrical foam 200 to escape to the outside when the inner surface of the cylindrical foam 200 is heat-sealed by the pinch roll 101. Is provided with a punching device 106 for punching the gas vent holes on the left and right sides of the cylindrical foam 200, and the punching device 106 is provided between the pinch roll 101 and the guide roller 102.

  As shown in FIG. 3, the punching device 106 includes a plurality of needle-like objects 106b provided around a rotatable roller 106a. In the present embodiment, the punching device 106 has a driving force. The needle-shaped object 106b that protrudes radially outward from the roller 106a is pressed against the side surface of the cylinder-shaped foam 200 that proceeds in the extrusion direction X. The degassing hole can be formed in the side surface of the cylindrical foam 200 while co-rotating with progress.

In the plate-like foam manufacturing apparatus according to the present embodiment, one punching device 106 is disposed on each of the left and right sides of the cylindrical foam 200, and the distance between the paired left and right punching devices is adjusted. By doing so, it is comprised so that the width | variety of the plate-shaped foam produced can be adjusted.
If the thickness of the needle-like object 106b of the punching device 106 is excessively small, it may be difficult to remove the gas from the cylindrical foam 200, and the plate-like foam 203 is adjusted to a desired width. It becomes difficult to do.
On the other hand, when the thickness of the needle-like object 106b is excessively large, the pressure inside the cylindrical foam 200 is excessively decreased, and it becomes difficult to make the plate-like foam 203 have a desired width.
Accordingly, the thickness (diameter) of the needle-like object 106b is preferably 0.5 to 5 mm, and more preferably 0.8 to 3 mm, in that the width of the plate-like foam 203 can be easily adjusted.

In addition, the tip shape of the needle-like object 106b is, for example, conical so that it is advantageous for the formation of the gas vent hole. However, if the needle-like object 106b has an excessively long shape, it may be bent or bent. Have
From such a viewpoint, the angle of the tip shape of the needle-like object 106b is preferably 10 to 45 degrees, and more preferably 10 to 30 degrees.

The perforating apparatus 106 preferably has an outer diameter of 50 to 200 mm indicated by a symbol A in FIG.
Moreover, 15-80 mm is preferable and the length of the needle-like object 106b shown with the code | symbol B in FIG.3 (b) is more preferable 30-70 mm.
Furthermore, the number of needles 106b of the punching device 106 is preferably 6-18.

Moreover, it is preferable to arrange | position the punching apparatus 106 on the right and left of the cylindrical foam 200 so that the needle-shaped object 106b may be located on the horizontal surface which passes along the center of the cylindrical foam 200, and it was drilled by the needle-shaped object 106b. It is desirable to arrange the gas vent holes so that they are located in the folded portions 2011 and 2012 of the cylindrical foam 200.
In order to obtain a product, the folded portions 2011 and 2012 are cut and removed by the cutter 105. However, the folded portions 2011 and 2012 can be provided with gas vent holes by the above-described method. The part that needs to be removed with a cutter can be kept to a minimum.

As described above, the punching device 106 is disposed in front of the pinch roll 101. However, if the distance between the pinch roll 101 and the punching device 106 is too close, the needle-like object 106b may come into contact with the pinch roll 101 and be separated. If it is too large, it will be difficult to stabilize the product width. Specifically, the distance from the surface connecting the central axes of the pinch rolls 101 paired up and down to the tip of the needle-like object 106b of the punching device 106 is 10 to 150 mm. It is desirable to install in.
In addition, in this position, the cylindrical foam 200 is normally cooled moderately and it is suitable also in the point which is easy to open a vent hole.

  The plate-like foam 203 produced using the production apparatus having such a perforating device 106 is different depending on the use of the plate-like foam 203 and the like. For example, a polystyrene resin and a bubble regulator And a plate-like foam having a thickness of 1 mm or more and 15 mm or less and having a thickness of 1 mm or more and 15 mm or less, which is foamed with a foaming agent so that the expansion ratio is 2 times or more and 30 times or less. It is done.

The polystyrene resin is not particularly limited, and examples thereof include styrene, α-methyl styrene, vinyl toluene, ethyl styrene, i-propyl styrene, t-butyl styrene, dimethyl styrene, bromostyrene, chlorostyrene, and the like. A homopolymer of a styrene monomer or a copolymer thereof can be used.
The polystyrene resin may be a copolymer of a vinyl monomer copolymerizable with the styrene monomer and the styrene monomer, and such a vinyl monomer. As, for example, alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cetyl (meth) acrylate, (meth) acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl In addition to fumarate and ethyl fumarate, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate are exemplified.
Furthermore, in this embodiment, a copolymer containing monomers other than these monomers can be employed as a raw material for forming the plate-like foam.

As the polystyrene resin used in the present embodiment, either an impact-resistant polystyrene resin (hereinafter also referred to as “HIPS”) or a general-purpose polystyrene resin (hereinafter also referred to as “GPPS”) is suitable.
The impact-resistant polystyrene resin (HIPS) contains a rubber component such as butadiene in addition to the styrene monomer. For example, the rubber component is copolymerized with the styrene monomer. Copolymers and those commercially available as blend resins of the copolymer and other homopolymers or copolymers may be employed.
Further, the general-purpose polystyrene resin (GPPS) is a resin component substantially composed of only a styrene monomer except for additives and the like.
Many of these polystyrene resins are commercially available, and are suitable not only because they are easily available but also relatively inexpensive.

As the polystyrene-based resin, when the cylindrical foam extruded from the discharge hole of the circular die is sandwiched between pinch rolls, the cylindrical foam is easily expanded with an internal gas mainly composed of a foaming agent. In this case, a resin exhibiting excellent elongation at a foaming suitable temperature is preferable.
By selecting such a resin, the maximum diameter of the cylindrical foam (the width of the plate-like foam) can be increased, and the ratio of the plate-like foam width to the circular die diameter can be increased.

For example, if the melt flow rate (MFR) of the polystyrene resin is too small, it is difficult to expand the cylindrical foam extruded from the circular die with gas pressure, and it is difficult to increase the ratio. .
On the other hand, if the MFR is excessive, the shape of the cylindrical foam becomes unstable, and it becomes difficult to stabilize the width of the produced plate-like foam.
Therefore, the MFR measured by JIS K7210 (Method B, 200 ° C., 49.03 N) is 0.00 in that the ratio can be ensured to be large and a wide plate-like foam can be stably produced. It is preferable to employ a 5 to 10 g / 10 min polystyrene resin, and it is particularly preferable to employ a 2.0 to 8.0 g / 10 min polystyrene resin.

The bubble regulator is not particularly limited as long as it is generally used as a bubble regulator. For example, talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide , Magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, inorganic compounds such as glass beads, and organic compounds such as polytetrafluoroethylene.
Among them, talc is particularly preferable as the bubble adjusting agent.
In addition, a bubble regulator may be used independently or may use 2 or more types together.

As the blowing agent, hydrocarbons such as propane, normal butane, isobutane, normal pentane, and isopentane can be used, and water, dimethyl ether, methyl chloride, ethyl chloride, nitrogen, carbon dioxide, argon, etc. are usually used. It is also possible to do.
As the foaming agent, it is also possible to employ compound particles that generate gas by thermal decomposition. Examples of the compound particles include azodicarbonamide, sodium hydrogen carbonate, a mixture of sodium hydrogen carbonate and citric acid, and the like. Can be used.

  In addition, if necessary, the polystyrene-based resin composition used for forming the plate-like foam can further contain a compounding agent used for forming a general resin foam molded article. Various stabilizers such as anti-aging agents, processing aids such as lubricants, slip agents, antifogging agents, pigments, fillers and the like can be appropriately added as additives.

  The plate-like foam according to the present embodiment can be produced by supplying a polystyrene-based resin composition containing the above components to the production apparatus, and is an extruder provided on the upstream side of the circular die 100. After melt-kneading the polystyrene-based resin composition and extruding and foaming the melt-kneaded product from the annular discharge hole of the circular die 100 to form the cylindrical foam 200, the inner surface of the cylindrical foam 200 is It can be produced by adopting a method in which the inner surface of the cylindrical foam 200 is heat-sealed by being pinched from above and below by a pinch roll 101 while it is not completely cooled.

At this time, it is preferable that the foaming is performed while blowing air from the air ring 103 to cool the surface of the cylindrical foam 200 extruded from the circular die 100.
The cylindrical foam 200 can be appropriately cooled by this air cooling, a skin layer is formed by cooling and solidification on the surface of the cylindrical foam, and it is possible to suppress excessive expansion by the internal gas and the cylindrical shape. It can also suppress that the bubble inside a foam expands too much.
Therefore, the maximum diameter of the cylindrical foam 200 can be adjusted by the air cooling, and the ratio of the product width to the circular die diameter can be adjusted.
However, since the excessive elongation is performed cooled tubular foam 200 is lost wide plate-like foam becomes difficult to obtain, the air cooling, the outer surface 1 m ² per 0 of the cylindrical foam 200. It is preferable to carry out by blowing air of 30 to 40 ° C. at a rate of 01 to 0.2 m ³ .
By carrying out such air cooling, the ratio (W / D) of the width (W) of the plate-like foam 203 and the diameter (D) of the circular die can be made 2 to 8 times. .

In this embodiment, since the punching device 106 is provided on the left and right of the cylindrical foam 200, the width (W) of the plate-like foam 203 can be adjusted by adjusting the interval between the punching devices 106. it can.
Further, by changing the position of the punching device 106 from the state in which the plate-like foam 203 is manufactured with a predetermined width, the width of the obtained plate-like foam 203 can be changed. Adjustment of the width | variety of the body 203 can be implemented by the following methods, for example.
That is, after measuring the total width (width before cutting both ends) of the plate-like foam 203 before the change, the left and right punching devices 106 are adjusted between the punching devices while adjusting their movement distances. Change the distance to match the plate-like foam width required after the change.
Next, the take-up speed of the plate-like foam is calculated by the following formula from the ratio of the total width (W ₀ ) of the foam sheet before the change and the full width (W ₁ ) after the change, and is adjusted to the speed.

Take-up speed after change = Take-up speed before change x (W ₀ / W ₁ )

The take-up speed is usually 5 m / min to 30 m / min, although it depends on the size of the plate-like foam to be produced.

Note that when the tubular foam 200 is sandwiched between the pinch rolls 101, the cross-sectional shape is crushed so as to be an elliptical shape extending in the width direction of the product while being pulled in the extrusion direction X by the take-up device 104. In addition, the cylindrical foam 200 has a stretching stress not only in the extrusion direction X (hereinafter also referred to as “MD direction”) but also in the width direction (hereinafter also referred to as “TD direction”). Will join.
Accordingly, the molecular orientation generated by the stretching stress is deformed in a direction that relaxes with time, and as a result, the plate-like foam is deformed such as warping or twisting.

Therefore, in the present embodiment, in order to prevent such deformation, extrusion foaming is performed so that the central portion of the upper sheet 201 and the central portion of the lower sheet 202 become the thin-walled portion Z. The plate-like foaming is performed such that the thin part Z of 201 and the thin part Z of the lower sheet 202 are overlapped at the central part in the width direction with the pinch roll 101 and the thickness of the central part is thinner than both ends. Form the body.
That is, in the present embodiment, it is important to form the thinned portion Z, which is thinner than the other portions, at two locations facing each other across the center of the cylindrical foam 200 in a continuous belt shape in the extrusion direction. Further, it is possible to heat-bond the thin-walled portions Z to form a portion that becomes the central portion in the width direction of the plate-like foam 203 so as to be thinner than both end portions, so that there is no risk of warping or the like. It becomes an important requirement in manufacturing the.

The thickness of the central portion is reduced because the stretching stress is most easily applied to the central portion, and when the plate-like foam is manufactured to a uniform thickness, the plate-like foam is visible in a time-dependent change (for example, after 5 days). This is because the body may be deformed, and the central portion may increase the thickness of the body more than other regions and cause deformation such as warpage in the plate-like foam.
In the point that such an increase in thickness can be absorbed more reliably, the thickness of the central portion of the plate-like foam immediately after its manufacture (for example, within 3 hours immediately after the manufacture) is 0 as compared with the thickness of both ends. The thickness is preferably 0.05 to 0.8 mm, and particularly preferably 0.1 to 0.5 mm.
The reason why the difference in thickness is preferably within the above range is that if it is less than the above range, an increase in the thickness of the central portion cannot be absorbed and the plate-like foam may be warped.
In addition, the upper limit as described above is provided for the preferable thickness difference, and if the difference exceeding the above range is provided, the thickness of the central portion increases, and conversely, the central portion is This is because there is a possibility of being in a depressed state.
In addition, about the difference of the thickness of the center part of this plate-shaped foam, and both ends, it can measure according to the method as described in the Example mentioned later, The thickness of the said center part is the thickness of the said both ends. When set to 100%, it is preferably 80% (-20%) to 99.5% (-0.5%), and 85% (-15%) to 99% (-1%). Is particularly preferred.

In addition, it is preferable that the plate-shaped foam which concerns on this embodiment is reducing thickness gradually as it goes to a center part from the width direction both ends, and when the total width of a plate-shaped foam is 100%, both ends It is preferable to form such that the region having a thickness of 1% or more with respect to the thickness of the part extends to a region of 25% or more (1/4 or more of the plate-like foam), and 50% or more (of the plate-like foam) It is preferably formed so as to cover a region of more than half.
In general, the upper limit is about 75%.

  Such a plate-like foam is less likely to be warped or twisted due to the passage of time immediately after production, and can be suitably used for display panels, food containers, etc., but the plate-like foam of the present invention Can be used for various applications as well as such applications.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

Example 1
To the extruder upstream of the tandem extruder connected with two extruders, 100 parts by mass of polystyrene resin (Toyo Styrene Co., Ltd., HRM-48N, MFR = 2.3 g / 10 min) and a bubble regulator As a foaming agent, 6.5 parts by weight of butane is press-fitted and melt-kneaded in the extruder, and the melt-kneaded product is continuously extruded on the downstream side. Then, the resin temperature was cooled to 145 ° C. by the downstream extruder, and extrusion foaming was performed from a circular die attached to the tip of the extruder to form a cylindrical foam.
The formed cylindrical foam was blown with air from an air ring immediately after extrusion to cool the outer surface and introduce it into a pinch roll.
In addition, the distance from the discharge port of the circular die to the pinch roll was set to 900 mm.
Also, the gap between the rolls of the pinch roll was set to 4.8 mm, and the cylindrical foam was sandwiched between the pinch rolls from above and below, and the inner surface was thermally fused to obtain a single plate-like foam.
A punching device 106 having a roller 106a with needles 106b as shown in FIG. 3 is arranged in front of the pinch roll (the distance between the surface connecting the central axes of the pinch rolls and the needle tip is 10 mm), and The degassing holes were drilled in the expanded cylindrical foam sheet placed at equal intervals from the central axis of the extrusion so that the distance between the central axes 1062 of the rollers of the left and right punching devices was 1045 mm.
The interval between the needle tip portions (needle tips) was about 950 mm.

At this time, the roller 106a on which the needle-like object 106b is arranged has a needle-like tip stuck in the cylindrical foam, continuously drilling holes on both sides while rotating smoothly, and in a stable state, the plate-like foam. I was able to get a body.
The total width of the obtained plate-like foam was about 970 mm.
About 25 mm at both ends including the portion where the vent holes were formed were removed from the plate-like foam by a cutter.
By the above manufacturing method, a plate-like foam 203 having a width of 920 mm and an expansion ratio of 18 was obtained.
At this time, thin plate portions were formed on the upper and lower sides of the cylindrical foam, and the plate-shaped foam was prepared such that the central portion in the width direction was thinner than both end portions.

<Thickness difference>
Five samples were collected from a region of 780 mm width 70 mm inside from both ends of the 920 mm width.
The sample collection location was as shown in FIG. 4, and 100 mm square samples were sampled at equal intervals (70 mm) in the width direction inside the 780 mm width.
Two samples were collected so as to be adjacent to each other in the MD direction, and two sets of five samples were collected.
Among them, a sample number of (1) to (5) is assigned to one set of samples in order from the end, a center line is drawn so as to be parallel to the width direction (TD direction) of each sample, and the center line is set to 4 The thickness at three equally divided points was measured with a thickness gauge having a minimum measurement unit of 0.01 mm, and the arithmetic average value was taken as the thickness of each sample.
Thus, when the thickness of the samples (1) and (5) at both ends and the sample (3) at the center was measured, both ends (1) and (5) in the width direction were thicker at 5.0 mm. It was confirmed that the central part (3) was 4.75 mm.
That is, it was confirmed that the difference in thickness between the both end portions and the center portion was 0.25 mm (the center portion was 5% thinner than both end portions).

<Diurnal change>
Moreover, the said sample was left still at normal temperature for 5 days, the thickness of each sample was measured by the same method as the above, and the secular change was observed.

<Heating deformation value>
Next, on the front and back of another set of samples ((1 ′) to (5 ′)) cut from a portion adjacent to the thickness measurement sample in the MD direction, a line segment of 100 mm is drawn in the TD direction. Was the length in the TD direction before heating.
And using a heating oven (manufactured by Yamato Scientific Co., Ltd., Fine Oven DH-41), quickly put a test piece in an oven set at 125 ° C. in advance, take it out quickly after 150 seconds, and measure the length of the line segment on both sides. The average value was the length in the TD direction after heating.
In addition, when the sample after heating was deformed and the line segment was bent or meandered to form a curve, the length of the line segment was measured along the curve, not the linear distance between both ends.
And the TD direction length [mm] after a heating was subtracted from the TD direction length [mm] before a heating, and it was set as the heating deformation value.
These evaluation results are shown in Table 1 below.

  As described above, it can be seen that the central portion (3) in the width direction of the plate-like foam is greatly deformed by heating and is likely to be deformed due to relaxation of molecular orientation.

(Example 2)
A plate-like foam was produced in the same manner as in Example 1. At that time, a gap between the rolls of the pinch roll was 6.6 mm, a plate-like foam having a width of 920 mm and a foaming ratio of 10 times was obtained. When the thickness of this plate-like foam was measured by the same method as described above, the width direction end portions (1) and (5) were thicker at 6.75 mm, and the center portion (3) was 6. It was confirmed that the thickness was 5 mm.
That is, it was confirmed that the difference in thickness between both end portions and the center portion was 0.25 mm (the center portion was 4% thinner than both end portions).
In addition, the heat deformation value and the thickness measurement after aging were measured by the same method as in Example 1. The results are shown in Table 2.

(Example 3)
A plate-like foam was produced in the same manner as in Example 2 except that the expansion ratio was set to 18, and the thickness and the like were measured.
As a result, as shown in Table 3 below, it was confirmed that the difference in thickness between the both end portions and the center portion was 0.25 mm (the center portion was 4% thinner than both end portions).

As described above, also in Examples 2 and 3, the widthwise central portion (3) of the plate-like foam is greatly deformed by heating, and is easily deformed due to relaxation of molecular orientation.
From the above, it can be seen that according to the present invention, a plate-like foam having a uniform thickness can be obtained, and warpage and twisting of the plate-like foam can be suppressed.

Claims (2)

After a polystyrene resin composition is extruded and foamed from a circular die to form a cylindrical foam, the foam is sandwiched between pinch rolls and the inner surface of the foam is thermally fused to obtain a plate-like foam. A method for producing a plate-like foam to be formed,
Forming the foam so that the thinned portion is thinner than the other portions at two locations facing each other across the center of the foam, and forming the foam so that the thinned portion is continuous in the extrusion direction, Forming a plate-like foam in which the thickness of the central portion in the width direction is thinner than that at both ends in the width direction by thermally fusing the portions together to form a portion that becomes the central portion in the width direction of the plate-like foam. A method for producing a plate-like foam characterized by the above.   The manufacturing method of the plate-shaped foam of Claim 1 which forms the said plate-shaped foam so that the thickness of the said width direction center part may become 0.5%-20% thin with respect to the thickness of both ends.

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