JPH0628889B2 - Method for producing styrene resin foam sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a styrene resin foam sheet.

(Prior Art) An extrusion molding method is widely used for producing a foamed sheet made of a styrene resin. In the extrusion molding method, a resin melt containing a foaming agent is made in an extruder, and the melt is extruded through a hole of a die attached to the tip of the extruder to continuously produce a molded product having a constant cross section. Is the way. According to the extrusion molding method, a molded body having a constant cross-section can be continuously and efficiently manufactured, so that the foamed sheet seems to be easily manufactured.

However, in practice, it is not easy to manufacture a wide sheet foamed at a high magnification by an extrusion molding method. The reason is that the resin containing the foaming agent foams immediately after it comes out of the die, resulting in a large distortion in the width direction. That is, immediately after extrusion, the expandable resin swells in each of the three-dimensional directions and increases the length in each of the three-dimensional directions.
Among them, only the length in the width direction does not have a means for easily absorbing the increase in the length, so that the length greatly undulates in the width direction, causing annoying deformation.

Further, even if the deformation in the width direction can be controlled by an appropriate means, the foamed sheet obtained by the extrusion method has a drawback that it is brittle as it is. That is, when the foamed sheet obtained by the extrusion method is used as it is, when it is bent, there is a drawback that the sheet is broken by a slight bending degree. However, it has been known that the above-mentioned drawbacks can be improved by allowing the thus foamed sheet to stand for a while under atmospheric pressure to be aged and then brought into contact with steam for secondary foaming.

Therefore, after the primary foaming by extrusion, steam was brought into contact with the foamed sheet to improve brittleness. However, it was said that the secondary foaming with water vapor had to be performed after leaving the primary foamed sheet in the atmosphere for a while. The reason for this is not clear, but it was thought that it was necessary for secondary foaming to occur after air, etc., penetrated into the bubbles created by the primary foaming and the air inside the bubbles reached equilibrium. Will. Therefore, conventionally, it was required to stand for a long time between the primary foaming and the secondary foaming, and for that reason, an aging step had to be provided. This is not an efficient manufacturing method. Therefore, it was necessary to do it more efficiently.

Japanese Unexamined Patent Publication (Kokai) No. 58-215328 proposes that styrene-based resin extruded from an extruder is first foamed and then immediately contacted with steam to carry out secondary foaming. However, the above publication states that the time for secondary foaming must be when the inside of the foam is at a high temperature and the surface portion is below the heat deformation temperature. The method taught in this publication is certainly effective in obtaining a foam having a large thickness. However, this method is not effective for a foam sheet having a small thickness. The reason is that in a sheet having a small thickness, the period in which the surface and the inside have different temperatures is short, and therefore it is difficult to capture the state where the inside is at a high temperature and the surface is below the heat deformation temperature. Further, since the above-mentioned publication is directed to a foam having a large thickness, it is necessary to extrude the foam in a shape having a desired cross-sectional shape as it is, and therefore, it cannot be directly applied to make a wide sheet having a small thickness. There wasn't.

(Problems to be Solved by the Invention) An object of the present invention is to efficiently obtain a foamed sheet that is uniformly foamed, has a small thickness, and has a wide width, and has improved brittleness.

(Means for Solving the Problem) The present inventor has to extrude a thin and wide foam sheet by
Do not extrude as a flat sheet, extrude into a cylindrical shape, and immediately after extruding, guide the cylindrical formed body onto a cylindrical mandrel, and expand the inner diameter while keeping the shape cylindrical, the width direction I found it convenient because it can prevent distortion. At the same time, the inventor cools the mandrel to forcibly cool the inner surface of the cylindrical resin, and when the cylindrical molded body is cut open to form a flat sheet, the inside of the sheet has a high temperature. It has been found that even if it does not occur, secondary foaming can be performed by contacting with steam immediately after the extrusion step, whereby the brittleness of the sheet is sufficiently improved.

Further, the present inventor, when enlarging the inner diameter as described above, sets the enlargement ratio to 1.2 times or more of the third root of the expansion ratio of the molded body, and then brings it into contact with water vapor and then taking it off after cooling. The rate is 1.01-1.3 compared to the rate before it was taken as a flat sheet before contact with steam.
It was found that when doubled, a good quality foamed sheet with particularly improved brittleness can be obtained. The present invention was made based on such knowledge.

This invention, a molten styrene resin containing a foaming agent is molded into a cylindrical shape under pressure and extruded into a low-pressure region, while advancing the foaming molded body while contacting with a cooled mandrel, The inner surface is cooled and the inner diameter of the molded product is expanded, and the expansion ratio is determined by the third root of the expansion ratio of the molded product.
1.2 times or more, then make a cut in the extrusion direction and develop it into a flat sheet for the first take-up, while continuing to proceed in a flat state, contact steam on both sides of the sheet, then cool. A method for producing a styrenic resin foam sheet, characterized in that the sheet is taken back again, and the subsequent take-up speed is set to 1.01 to 1.3 of the initial take-up speed.

An example of the implementation of the method of the present invention will be described below with reference to the drawings. FIG. 1 is a model diagram showing the method of the present invention together with an apparatus. In FIG. 1, 1 is an extruder, 2 is a die, 3 is a mandrel, 4 is a mandrel support, 5 is a knife, 6 is a primary foam sheet, 7 is a first take-up roll, 8 is a steam tank, and 9 is Second take-up roll, 1
0 is a secondary foam sheet.

In FIG. 1, the method of the present invention is performed as follows.
First, a melt of a styrene resin containing a foaming agent is made in the extruder 1, the melt is formed into a cylindrical shape in the die 2, and extruded into the atmosphere. The extruded cylindrical molded body immediately foams. Further, the molded body advances while contacting the mandrel 3. Since the outer diameter of the mandrel 3 is larger than the inner diameter of the cylindrical molded body, the inner diameter of the molded body is enlarged while the molded body travels along the mandrel. The expansion rate is 1.2 times or more the third root of the expansion ratio of the molded product. Further, since the mandrel 3 is cooled, the inner surface of the molded body is forcibly cooled and the outer surface is exposed to the atmosphere to be cooled. Thus, the molded body is prevented from being distorted in the width direction and uniformly foams.

The molded body, which has been foamed and whose inner surface has been cooled, is scored in the axial direction by the knife 5 and is spread flat to become the primary foamed sheet 6. The sheet 6 is taken up by the first take-up roll 7, and thereafter advances as a flat sheet as it is. The sheet is put into the steam tank 8 at the tip of the sheet, and steam is applied from both front and back sides in the tank 8 to cause secondary foaming. The sheet exiting from the tank 8 is cooled by the atmosphere and is heated to a temperature equal to or lower than the heat distortion temperature to become a secondary foamed sheet, which is then taken up by a second take-up roll 9 and then taken up by a take-up roll for secondary foaming. It becomes the product of sheet 10. At this time, the take-up speed by the second take-up roll 9 is 1.01 to 1.3 times the take-up speed by the first take-up roll 7.

(Effect of the Invention) According to the method of the present invention, the melt of the styrenic resin containing the foaming agent is molded into a cylindrical shape under pressure and extruded into the low-pressure region, so that a foamed cylindrical molded body is continuously produced. be able to. Next, since the cylindrical molded body thus produced is advanced while being brought into contact with the cooled mandrel, the inner surface of the molded body can be forcibly cooled, and the inner diameter of the molded body can be expanded to increase the width direction of the foam. Deformation can be prevented. At that time, the expansion ratio of the inner diameter is 1.2 of the third root of the expansion ratio of the molded product.
Since the number is twice or more, the extruded foam sheet is greatly expanded in the direction perpendicular to the extrusion direction, and therefore the deformation in the width direction is reduced. In this way, it is possible to easily produce a cylindrical molded body having a large diameter and uniform diameter and no distortion.

Next, a cut is made in the width direction of the obtained cylindrical molded body, and a flat sheet is developed and taken out, so that a wide sheet can be easily obtained. Further, since the sheet is unfolded, the mandrel and the cutting tool can be supported from the unfolded side, so that the mandrel and the like can be easily attached.
In addition, since the sheet is expanded and continuously advanced in a flat state, it is possible to evenly contact the water vapor on both the front and back surfaces of the sheet, and because of its thin thickness, secondary foaming can be easily performed subsequent to primary foaming. It can be carried out. In this way, the secondary foamed sheet is taken off after cooling, and the take-up rate after cooling is 1.01 to 1 of the take-up rate of the flat sheet before contact with steam.
Since it is set to 3 times, it is possible to easily and efficiently make a foamed sheet having a uniform width and a high degree of foaming and having improved brittleness and having a thin width. The present invention provides such advantages.

(Explanation of each requirement) Excluding the enlargement ratio of the inner diameter of the cylindrical molded body from the first half step of the present invention, and removing the proportion of the take-up speed from the latter half step, if these are separated and viewed separately, which step Is also known. That is, the process itself of obtaining a tubular foam by extrusion molding and expanding the tubular foam to obtain a flat primary foam sheet is known. The step of contacting the thus obtained primary foam sheet with steam to obtain a secondary foam sheet is also known per se. However, in the known method, the primary foaming step and the secondary foaming step are performed separately. Moreover, at least several days of aging, that is, aging, is required between the primary foaming step and the secondary foaming step. However, the present invention is unique in that the primary foaming step and the secondary foaming step are continuously performed. Moreover, according to the present invention, by performing the above-mentioned two steps continuously, and by further specifying the above-mentioned inner diameter expansion ratio of the cylindrical molded body and the ratio of the take-up speed of two times, it is possible to efficiently obtain a good quality foamed sheet It brings a great advantage that it can be obtained easily and easily.

In this invention, a styrene resin is used as the resin. The styrene-based resin is not limited to a homopolymer of a styrene-based monomer, but includes a copolymer. For styrene-based monomers,
In addition to styrene, methylstyrene and ethylstyrene are also included. Further, the copolymer includes a copolymer containing 50 mol% or more of a styrene-based monomer. Examples of the counterpart monomer of the copolymer include methyl methacrylate, acrylonitrile, maleic anhydride and the like. Among them, preferred resins are polystyrene, styrene-acrylonitrile copolymer, and styrene-maleic acid copolymer.

The blowing agent used in the method of the present invention is a caustic aliphatic hydrocarbon or a halogenated aliphatic hydrocarbon having a boiling point lower than the heat distortion temperature of the styrene resin. The aliphatic hydrocarbon is, for example, a saturated aliphatic hydrocarbon such as propane, butane, pentane and hexane, and an unsaturated aliphatic hydrocarbon such as propylene and butylene. The halogenated aliphatic hydrocarbon is, for example, methyl chloride, methylene chloride, dichlorodifluoromethane or the like. These may be used alone or in admixture of two or more.

The location where the resin contains the foaming agent may be before the resin is supplied to the extruder or in the middle of the extruder. The extruder may be a single screw type or a twin screw type. The resin is melted under pressure in the extruder.

When extruding, it is necessary to mold the foamable resin into a cylindrical shape and extrude it. For this purpose, a die is attached to the tip of the extruder, an annular slit is provided in the die, and the resin is extruded from this slit.

A mandrel is attached to the tip of the base, and the mandrel has a columnar side close to the base. Mandrel
It is preferable that the side closer to the base is thin and the side away from the base is thicker, but it may have the same diameter. The mandrel may be shaped so that it gradually expands into a flat surface on the side away from the base. In any case, the outer diameter of the mandrel on the side away from the die is much larger than the outer diameter of the circle in the gap of the die, and is larger than the outer diameter after the cylindrical molded body extruded from the die is expanded by natural foaming. Has also been made larger. The mandrel is attached to the extension of the inner mold forming the annular gap in the base. Therefore, the cylindrical molded body extruded from the slit is
The mandrel will be surrounded by bubbles. During this process, the shaped body comes into contact with the outer surface of the mandrel and is enlarged in its inner diameter by the outer surface of the mandrel and is therefore always kept taut in the circumferential direction. As a result, the molded body is prevented from being distorted in the circumferential direction, that is, the width direction.

The outer surface of the mandrel is cooled. Cooling can also be performed by supplying and discharging the cooling medium from the die side, but in the method of the present invention, the cylindrical molded body is cut open at the tip of the mandrel, so the cooling medium is supplied from the cut end. And, as discharging, cooling can be performed. In the first place, the mandrel and the knife can be attached by fixing them to the mouthpiece side, but they can also be installed by supporting the molded body on the cut open side.

The cylindrical molded body has its inner surface cooled and its inner diameter enlarged while advancing on the mandrel. Meanwhile, the outer surface of the cylindrical molded body is brought into contact with the atmosphere and is naturally cooled from the outer surface. In this way, the cylindrical molded body becomes a cooled foamed tube having a large inner diameter.

The foam tube is axially scored, unfolded and taken up as a flat sheet. The take-up is performed by being sandwiched between a pair of take-up rolls or a belt attached thereto. In this way, a sheet having primary foaming is obtained. The first take-up roll takes out the primary foamed sheet.

After passing through the first take-up roll, the primary foamed sheet continues to proceed in a flat state and enters the steam tank for secondary foaming. The steam tank is, for example, a rectangular parallelepiped box, steam tubes are attached along the ceiling and the bottom, and holes are bored in the tank at some places of the steam tubes. It is designed to be filled with water vapor. A pair of opposed side walls in the tank are provided with horizontally extending slits, through which the primary foam sheet enters the tank,
In addition, it goes through the slit and goes out of the tank. The inside of the tank may be divided into several parts, and water vapor may be ejected in each area.

Water vapor that should come into contact with the primary foam sheet is 80 ° C to 1
It is preferably 20 ° C. For this, use gauge pressure
It is desirable to supply steam of about 0.1 to 0.02 kg / cm ² to the steam pipe. The time during which the primary foam sheet should contact the water vapor is appropriately set within the range of 10 seconds to 300 seconds. Since the purpose is to foam the primary foam sheet with steam in the tank, the sheet must be held so that it can be freely foamed in the tank. For this purpose, it is desirable to stop supporting the sheet over a large area and only lightly support the sheet from the bottom at a largely hanging portion. In this way, the primary foam sheet is secondary foamed in the tank.

The secondary foamed sheet exits the steam tank and is exposed to the atmosphere to be cooled. When cooled to a temperature below the heat distortion temperature of the resin, the sheet is taken up by the second take-up roll. After that, the sheet is wound on a winding roll to be a product.

In this invention, the inner diameter of the tubular molded body is enlarged by the mandrel, and the enlargement ratio at that time is represented by the ratio of the maximum diameter of the mandrel and the inner diameter of the annular gap in the die, which is referred to as the blow-up ratio. I'm calling.
Blow-up ratio is abbreviated as BUR. In the present invention, the third root of the expansion ratio of the BUR cylindrical molded body is 1.
18 times or more. Further, in the present invention, the take-up speed by the second take-up roll is set to the take-up speed by the first take-up roll.
Set to a range of 1.01 to 1.3 times.

These things were decided based on the result of the experiment. That is, in the present invention, the BUR is 1.2 times or more the cube root of the expansion ratio of the primary foam sheet, so that the primary foam sheet is greatly expanded in the direction perpendicular to the extrusion direction (hereinafter referred to as the axial direction). Become. The reason why the take-up speed of the second take-up roll is 1.01 to 1.3 times the take-up speed of the first take-up roll is 1.01 times or less. On the contrary, the above take-up speed ratio
This is because if it is 1.3 times or more, the sheet is too strongly pulled in the extrusion direction in the steam chamber, and the effect of improving brittleness is reduced.

Here, the cube root of the expansion ratio in the foam molded article is 3, for example, if the foam molded article is foamed 27 times. Therefore, in this case, the expansion rate is 3.6.
It must be above.

Thus, by limiting the expansion ratio of the cylindrical molded body by the mandrel, and also by limiting the ratio of the subsequent take-up speed and the initial take-up speed, it is possible to obtain a foamed sheet in which brittleness is particularly well improved. it can.

The details of the method of the present invention will be described below with reference to Examples and Comparative Examples, and the reason why the method of the present invention is excellent will be clarified. The flexural flexure amount, flexural strength, and flexural modulus at the time of flexion were measured in Examples and Comparative Examples.
It was measured by the method defined by IS K 7203-1973. However, the test piece had an original fabric thickness × width (50 mm) × length (150 mm) and a span interval of 50 mm.

Example 1 In this example, two extruders having 90 mm and 150 mm caliber were connected as an extruder, polystyrene was used as a resin, and 0.5% by weight of talc was compounded as a nucleating agent and supplied to the extruder. did. Butane was used as the foaming agent.

As the die, one having an annular gap having a gap width of 0.75 mm and a diameter of 105 mm was used. A cylindrical mandrel having an outer diameter of 312 mm and a length of 420 mm was used. As the steam tank, only one steam chamber having a length of 3 m was used.

The polystyrene resin having the above composition was fed to an extruder, butane was contained in the extruder at a ratio of 4.7% by weight to the resin, the die temperature was maintained at 145 ° C., and the resin was extruded at a rate of 90 kg / hour. A cylindrical molded body was prepared by advancing it on a mandrel, cooling the mandrel surface while maintaining it at 40 ° C., expanding the diameter, and performing primary foaming at a take-up speed of 10.9 m / min by the first take-up machine. . Thus, the thickness
1.60 mm, width 975 mm, basis weight 140 g / m ² , foaming ratio 12.0
A double primary foam sheet was obtained. At this time, the BUR was 1.30 times the cube root of the expansion ratio of the primary foam sheet.

Secondary foaming was performed subsequent to the above primary foaming. In the secondary foaming, 0.08 kg / cm ² of steam is sent at a gauge pressure to the steam pipe arranged in the steam tank having a length of 3 m, and the steam tank is filled with 100 ° C. steam to form a primary foamed sheet. After heating, the secondary take-up speed was 11.2 m / min for secondary foaming. Thus, the thickness is 2.90 mm, the width is 993 mm, and the basis weight is 1.
A secondary foam sheet having 37 g / m ² and an expansion ratio of 22.2 was obtained. When the brittleness of this sheet was measured, the amount of bending and bending when it was broken by bending was 3.89 mm in the extrusion direction,
9.62 mm in width direction, bending strength is 20.0 kg / cm ² in extrusion direction,
5.9 kg / cm ^{2 in} width direction, flexural modulus 910 kg in extrusion direction
/ Cm ² and 160 kg / cm ² in the width direction, it was confirmed that the brittleness was improved. Moreover, the bending strength and the bending elastic modulus were improved.

Comparative Example 1 This comparative example was carried out in much the same way as in Example 1, except that the mandrel diameter was reduced to a BUR of 2.8 and the take-up speed before and after was slightly increased. It was

That is, the same resin was put into the same extruder as in Example 1, and the same foaming agent was press-fitted and extruded and foamed from the same die. However, the mandrel had an outer diameter of 312 mmφ and a length of 420 mm.
The primary foaming was performed at a first take-up speed of 9.5 m / min. Thus, a primary foam sheet having a thickness of 2.17 mm, a width of 975 mm, a basis weight of 172 g / m ² , and a foaming ratio of 13.2 was obtained. The conditions of the steam tank at the time of secondary foaming were the same, but the second take-up rate was 13.0 / min. Thus, the thickness
2.98 mm, width 934 mm, basis weight 133 g / m ² , foaming ratio 23.5
A secondary foam sheet of was obtained.

When the brittleness of this sheet was measured, the flexural bending amount when breaking due to bending was 3.09 mm in the extrusion direction, 10.6 mm in the width direction, and the bending strength was 13.8 kg / cm ^{2 in} the extrusion direction and 3.3 kg in the width direction. / Cm ² , flexural modulus is 800 kg in extrusion direction
/ Cm ² and 70 kg / cm ² in the width direction, the brittleness was improved, but it was recognized that it was inferior to Example 1.

Comparative Example 2 This comparative example was carried out using the same extruder and the same resin as in Example 1, but changing the die, the mandrel and the steam tank.

As the die, an annular gap having a gap width of 1 mm and a diameter of 110 mm was used. A cylindrical mandrel having an outer diameter of 330 mm and a length of 420 mm was used.
As the steam tank, two steam chambers each having a length of 3 m were arranged in close contact with each other to have a total length of 6 m.

As in Example 1, a resin containing butane was melted in an extruder, extruded as a cylindrical molded body from the die, passed over the mandrel, and then taken by a first taker at a speed of 8.6 m / min to obtain a thickness. 2.30mm, width 1045mm, basis weight 176
A primary foam sheet having a g / m ² expansion ratio of 13.7 was obtained. This sheet was subsequently subjected to secondary foaming in a steam tank having a length of 6 m. At this time, steam with a gauge pressure of 0.05 kg / cm ² was introduced into the steam tank. The second take-up speed was 12.4 m / min. The secondary foam sheet thus obtained had a thickness of 3.30.
mm, width 965 mm, basis weight 130 g / m ² , foaming ratio 56.7
It was double.

Measurement of the brittle for this sheet, 3.40 mm deflection amount bending in the extrusion direction, 10.1 mm in width, bending strength 12.0 kg / cm ² in the extrusion direction, 3.10kg / cm ² in the width direction, bending elasticity modulus It was 570 kg / cm ² in the extrusion direction, and it was confirmed that the brittleness was improved, but the degree of the improvement was insufficient as compared with the examples.

As seen through Example 1 and Comparative Examples 1 and 2, the BUR of Example 1 is the cube root of the expansion ratio (hereinafter, referred to as E ₁ ) of the primary foam sheet, that is, The primary take-up speed is 1.30 times the primary take-up speed.
03 times, the BUR of Comparative Example 1 1.18 times, the secondary take-up speed is 1.25 times the primary take-up speed, and the BUR of Comparative Example 2 is 1.25, the secondary take-up speed is 1.44 times the primary take-up speed, and the BUR is Is 1.2 times or more, and the secondary take-up speed is 1.01-1.
It was confirmed that the brittleness and the physical properties of the obtained foamed sheet were further improved when it was in the range of 30 times.

[Brief description of drawings]

FIG. 1 is a model diagram of the method of the present invention. In the figure, 1 is an extruder, 2 is a die, 3 is a mandrel,
4 is a support base, 5 is a knife, 6 is a primary foamed sheet, 7 is a first take-up roll, 8 is a steam tank, 9 is a second take-up roll, and 10 is a wound secondary foamed sheet.

Claims (1)

[Claims] 1. A styrene-based resin melt containing a foaming agent is molded into a cylindrical shape under pressure and extruded into a low pressure region, and a foaming molded body is advanced while contacting with a cooled mandrel. The inner surface of the molded body is cooled and the inner diameter of the molded body is expanded.
1.2 times or more, then make a cut in the extrusion direction and develop it into a flat sheet for the first take-up, while continuing to proceed in a flat state, contact steam on both sides of the sheet, then cool. A method for producing a styrenic resin foam sheet, characterized in that the sheet is taken up again and the subsequent take-up speed is made 1.01 to 1.3 times the original take-up speed.