JP2021014529A - Foamed sheet production method - Google Patents

Abstract

To provide a foamed sheet production method in which the tension of each portion in the process of taking off a resin sheet does not become excessive in extrusion foam molding using a T-die.SOLUTION: A production method for foamed sheets includes an extrusion process of extruding the expandable resin sheets from an extruder equipped with a T-die and a cooling process of cooling the resin sheet. In the cooling process, the resin sheet is cooled by a first chill roll (A) disposed just after a die exit and having a drive mechanism, a take-up speed decision roll arranged rearward the first chill roll and deciding a resin sheet take-up speed, and one or more chill rolls (group)(B) arranged between the first cooling roll and take-up speed decision roll, and the resin sheet is taken off in such a state that a tension of the resin sheet does not become excessive.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a foam sheet. Specifically, a foaming ratio larger than 2.1 times and 20 Vol. The present invention relates to a method for producing a foamed sheet containing a foamed layer having an open cell ratio lower than%. More specifically, the present invention relates to a method for producing a foamed sheet, which includes an extrusion step of extruding a foamable resin sheet by an extruder equipped with a T-die and a cooling step of cooling the resin sheet.

In extrusion foam molding of a thermoplastic resin, a T die or a circular die is generally used. When an excellent appearance is required, extrusion foaming using a T-die is widely used because transfer by a roll and smoothing of the surface are easy.

In particular, when a thermoplastic resin having crystallinity such as polypropylene is foam-molded by an extruder equipped with a T-die, the surface characteristics of the sheet can be improved by forming fine closed cells. In order to improve the surface properties of the sheet, in addition to the material properties, a cooling step when the molten resin discharged from the die is taken over and the sheet is molded is important. It has been reported that special cooling equipment and cooling methods are used to cool and stop the growth of generated bubbles in a fine state. Furthermore, it has been reported that a special cooling facility or cooling method is used to eliminate the wavy phenomenon in the width direction of the foamed sheet, which is called corrugated.

For example, Patent Document 1 discloses a method for manufacturing a sheet in which a take-up roll is installed at a position close to a die outlet and a cooling roll is installed after the take-back roll. Patent Documents 2 and 3 disclose an apparatus provided with a multi-stage cooling roll in the vicinity of the die outlet. Patent Document 4 discloses a method in which a pre-cooling roll is provided after the die outlet and a cooling medium is sprayed on the sheet. Patent Document 5 discloses a method of manufacturing a sheet by an apparatus including a plurality of interlocking cooling rolls.

Patent No. 3597266 Patent No. 6171717 Patent No. 6232832 JP 2001-347560 Patent No. 5457077

As described above, it is possible to enhance the cooling of the molten resin by a device provided with a cooling roll at a position close to the die outlet. Further, by using the above-mentioned multi-stage cooling roll, both surfaces of the resin sheet can be quickly cooled, and the appearance of the sheet can be greatly improved.

However, especially when the foaming ratio is large, it is difficult to achieve both a good open cell ratio and an excellent appearance by the conventional method. In addition, it is difficult to adjust the conditions, and it depends largely on individual experience.

That is, in T-die extrusion foaming, in order to enhance the cooling of the molten resin and improve the appearance, it is possible to cool both sides of the resin sheet with a first cooling roll close to the die and a subsequent cooling roll group. is important. In this cooling process, the volume of the sheet expands due to foaming and the volume of the sheet decreases due to cooling and solidification. Therefore, it is necessary to maintain a good state of taking over the resin sheet at each stage of the cooling process. If the resin sheet is not in good condition, the following problems may occur.

First, when the volume of the sheet expands in the process of foaming the molten resin discharged from the die, if the tension generated by taking over the resin sheet is too strong, the resin sheet is excessively stretched and becomes large. Tension is generated, and foaming defects such as crushing of bubbles and rupture of bubbles occur. On the contrary, if the tension generated by taking over the resin sheet is too weak, the above-mentioned corrugation becomes remarkable and the appearance is deteriorated.

Secondly, even in the process of cooling and solidifying the resin sheet, if the tension applied to the resin sheet becomes too large, foaming defects such as crushing of bubbles and rupture of bubbles occur. On the contrary, if the force for pulling the resin sheet is made too weak in order to relax the tension of the sheet, the sheet will be wrinkled and the appearance will be poor. Further, since the resin sheet and the cooling roll do not adhere well, the cooling efficiency is lowered and the open cell ratio becomes excessively high.

That is, since the volume of the resin sheet increases or decreases in each process during sheet molding, if an excessive tension is generated in the resin sheet, the above-mentioned foaming failure occurs.

However, it is very difficult to find suitable sheet pick-up conditions when equipment equipped with a multi-stage cooling roll is used. In particular, as the expansion ratio increases, the expansion and contraction of the volume of the resin sheet described above increases. In addition, the growth of bubbles in the foaming process becomes faster, and the ratio of bubbles to the sheet volume increases. As a result, the resin sheet is liable to be crushed, and bubbles are liable to coalesce and rupture. In such a case, it becomes more difficult to adjust the conditions for picking up the resin sheet with an appropriate tension.

Regarding this point, for example, Patent Document 1 describes that a cooling roll is brought close to the outlet of the die. Further, it is described that the distance between the die and the cooling roll and the angle θ in the direction in which the cooling roll picks up the resin sheet are adjusted. However, Patent Document 1 does not describe controlling the tension of the resin sheet. Moreover, the importance of the roll driving method is not described.

Further, Patent Document 1 describes only examples in which the foaming ratio is up to 2.1 times. Therefore, when the foaming ratio is further increased, it is not always possible to mold the sheet well. In practice, when the foaming ratio becomes large, it is good to adjust the first cooling roll and the subsequent cooling rolls (groups) to control the tension of each part in the cooling process of the resin sheet. It is very important to get the sheet.

Further, in the case of a facility having a plurality of cooling rolls, it is necessary to individually adjust the speed of each of the plurality of cooling rolls in order to make the tension of the resin sheet between the cooling rolls appropriate from the same viewpoint. .. However, for example, even if the speed of each cooling roll is controlled independently, it is difficult to visually confirm the state of the resin sheet being taken over. For this reason, the molded resin sheet is sampled to measure the expansion ratio, open cell ratio, and the like. Also, observe the bubble morphology of the cross section of the resin sheet. Based on these results, the state of the resin sheet is evaluated, and the work of changing the roll speed or the like based on the evaluation results is repeated. As described above, it takes a long time to adjust the speed of each roll to a suitable range. If the time required for adjusting the conditions becomes long, the material loss during the production of the foamed sheet increases. In addition, it is necessary to adjust the speed condition of each roll as described above every time the foaming state is changed by changing the foaming ratio or the material composition. For this reason, a method capable of easily adjusting the tension of the sheet and producing a good foamed sheet is desired.

As described above, in the extrusion foam molding using the T die, the foaming ratio is larger than 2.1 times and 20 Vol. Easily obtaining a foamed sheet having an open cell ratio lower than% and having an excellent appearance has been an unsolved problem.

In view of such circumstances, it is an object of the present invention to provide a method for producing a foamed sheet in which the tension of each part in the process of taking over the resin sheet is not excessive in extrusion foam molding using a T-die. Another object of the present invention is to provide a method for producing a foamed sheet, which has an excellent appearance and can easily obtain a foamed sheet having a high foaming ratio and a low open cell ratio.

In extrusion foam molding using a T-die, the present inventors can easily obtain a foamed sheet having an excellent appearance and a high foaming ratio by taking the sheet in a state where the tension of the sheet is not excessive. I found that. Specifically, the first cooling roll (A), which is arranged immediately after the die outlet and has a drive mechanism, and the first cooling roll (A), which is arranged behind the first cooling roll, determines the take-up speed of the resin sheet. The sheet is cooled by one or more cooling rolls (groups) (B) arranged between the roll and the first cooling roll and the take-up speed determination roll, and the tension of the sheet is not excessive. We have found that a good foamed sheet can be easily obtained by taking over the sheet, and have reached the present invention.

That is, the present invention includes the following.
[1]
A method for manufacturing a foam sheet made of a thermoplastic resin.
The foamed sheet has a foaming ratio greater than 2.1 times and 20 Vol. Contains a foam layer with an open cell ratio of less than%
It includes an extrusion step of extruding a foamable resin sheet by an extruder equipped with a T-die and a cooling step of cooling the resin sheet.
In the cooling step, the first cooling roll (B) having a drive mechanism, which is arranged immediately after the die outlet, and the first cooling roll (B), which is arranged behind the first cooling roll, determines the take-up speed of the resin sheet. The resin sheet is cooled by one or more cooling rolls (groups) (B) arranged between the roll and the first cooling roll and the take-up speed determination roll, and the tension of the resin sheet does not become excessive. A method for manufacturing a foamed sheet, which comprises taking over a resin sheet in a state.

[2]
When the take-up speed of the resin sheet by the first cooling roll (A) is R1 and the take-up speed of the resin sheet by the take-back speed determination roll is R2, the relationship of R2 × 1.10 ≧ R1 ≧ R2 × 0.90 is satisfied. , [1]. The method for producing a foam sheet.

[3]
The method for producing a foam sheet according to [1] or [2], wherein the outer diameter of the first cooling roll (A) is 300 mm or less.

According to the method for producing a foamed sheet of the present invention, it is possible to adjust the conditions so that the tension of the sheet does not become excessive. Further, even if the foaming ratio is high, the crushing of air bubbles during molding is reduced, and a foamed sheet satisfying good foaming characteristics and excellent appearance can be obtained.

Further, the molded product using the foamed sheet of the present invention is excellent in impact resistance, light weight, rigidity, heat resistance, heat insulating property, oil resistance and the like. The molded product using the foam sheet of the present invention includes trays, plates, food containers such as cups, automobile door trims, automobile trunk mats and other vehicle interior materials, and building materials that can be heated by a microwave oven and filled with hot beverages. , Packaging, stationery, etc. can be suitably applied.

An example of the configuration of the entire facility for picking up the resin sheet is shown. An example of the configuration of the entire facility for picking up the resin sheet is shown. An example of the configuration of the entire facility for picking up the resin sheet is shown. An example of the configuration of the entire facility for picking up the resin sheet is shown.

Hereinafter, embodiments of the present invention will be described in detail.

1. 1. First cooling roll (A)
Hereinafter, the first cooling roll (A) of the present invention will be described.
The first cooling roll (A) needs to be placed immediately after the die outlet. The term "immediately after the die outlet" as used herein means that the shortest distance between the die outlet and the surface of the first cooling roll (A) is greater than 0.01 mm and 50 mm or less. Within this range, the distance between the die outlet and the surface of the first cooling roll (A) can be adjusted according to the thickness of the resin sheet and the foamed state of the resin. In general, this distance increases as the thickness of the sheet of interest increases. From the viewpoint of suppressing corrugation and cooling the sheet in a short time, it is desirable to arrange the first cooling roll (A) closer to the die as long as the appearance is not affected. On the other hand, if the first cooling roll (A) becomes too close to the die, the first cooling roll (A) bends due to the load from the sheet during molding of the sheet, and the first cooling roll (A) becomes a die. Contact may cause molding defects or damage to the equipment. Therefore, the distance between the die and the first cooling roll is more preferably greater than 0.1 mm and more preferably 50 mm or less.

The arrangement of the first cooling roll (A) in the direction perpendicular to the extrusion direction is not particularly limited and can be freely selected according to the foamed state of the molten resin. By adjusting the height of the first cooling roll (A), it is possible to prevent the volume of the resin sheet from expanding excessively while rapidly cooling the molten resin discharged from the die. As a result, it is possible to suppress the occurrence of corrugations in the produced foam sheet.

The first cooling roll (A) needs to be provided with a drive mechanism capable of controlling the speed independently of the other rolls or a mechanism capable of controlling the tension. Such a mechanism is necessary to adjust the tension of the sheet during molding of the sheet. The drive mechanism of the first cooling roll (A) is not particularly limited as long as the roll speed can be controlled. A general inverter motor, an AC servo motor, or the like can be applied to the drive mechanism of the first cooling roll (A). The first cooling roll (A) can be driven by transmitting the power of the motor to the first cooling roll (A) by using a gear, a belt, or the like.

By independently controlling the speed of the first cooling roll (A), it is possible to make a difference between the take-up speed determined by the take-up speed determination roll and the speed of the first cooling roll (A). Is. This makes it possible to adjust the tension of the sheet in the entire cooling roll (group). By adjusting the tension of the sheet, it is possible to form a sheet having an excellent appearance while suppressing bubble crushing in the cooling process of the resin sheet. Adjusting the difference between the speed of the first cooling roll (A) and the speed of the take-up speed determining roll is very important for adjusting the tension of the resin sheet during molding, especially when the foaming ratio is large. Is important to.

The outer diameter of the first cooling roll (A) is preferably 300 mm or less, more preferably in the range of 30 to 300 mm. When the outer diameter of the first cooling roll (A) is 300 mm or less, the arrangement of the first cooling roll (A) can be finely adjusted. Further, even when the first cooling roll (A) is brought close to the die, the angle between the surface of the first cooling roll (A) and the resin sheet to be taken can be reduced. As a result, it is possible to reduce the tension generated in the sheet in the foaming process, and it is possible to suppress the crushing of air bubbles in the sheet cooling process. Further, when the take-up speed is the same and the arrangement of the roll and the sheet is the same, the smaller the outer diameter of the first cooling roll (A), the shorter the time is to guide the sheet to the subsequent second cooling roll. be able to. As a result, both surfaces of the resin sheet can be cooled quickly. Further, since the contact time between the first cooling roll and the resin is shorter than when the outer diameter of the roll is large, the first cooling is performed in a state where the first cooling roll (A) is sufficiently cooled. The roll (A) can be used continuously. If the outer diameter of the first cooling roll (A) becomes too large, cooling on the surface of the sheet that is not in contact with the first cooling roll (A) is delayed, so that insufficient cooling tends to cause foaming defects. Further, when the first cooling roll (A) is close to the die, the angle between the extrusion direction of the molten resin from the extruder and the take-up direction of the resin sheet becomes large, so that bubbles are crushed in the sheet cooling process. It becomes easy and foaming failure is easy to occur. On the contrary, if the outer diameter of the first cooling roll (A) becomes too small, the strength of the first cooling roll (A) becomes insufficient, so that the roll bends or bends due to the tension of the resin sheet. Is prone to malfunction.

The structure of the first cooling roll (A) is not particularly limited. It is desirable that the first cooling roll (A) has a structure for controlling the temperature by passing a cooling medium such as water inside in order to stably cool the sheet. For example, the first cooling roll (A) may have a single tube structure inside. In order to further improve the cooling efficiency, the first cooling roll (A) may have a double pipe structure, a jacket structure, or the like.

The temperature of the cooling medium used for the first cooling roll (A) is not particularly limited as long as it is a temperature suitable for cooling the resin sheet. The temperature of the cooling medium used for the first cooling roll (A) is preferably 5 to 40 ° C. in order to sufficiently cool the sheet. If the temperature of the cooling medium used for the first cooling roll (A) is too high, the resin is not sufficiently cooled, and the bubbles may become coarse. In addition, the bubbles may coalesce to increase the open cell ratio. In addition, corrugations may occur prominently. If the temperature of the cooling medium used for the first cooling roll (A) is too low, water is generated on the surface of the roll due to dew condensation, and this water may deteriorate the appearance of the sheet.

Further, it is desirable that the first cooling roll (A) is provided with a mechanism for keeping the distance from the die constant during extrusion foam molding. Specifically, for example, it is preferable that the die and the first cooling roll (A) are fixed by a common support. Alternatively, when the die and the first cooling roll (A) are installed on separate pedestals, it is preferable that the pedestals are fixed to each other. By keeping the distance between the first cooling roll (A) and the die constant during extrusion foam molding, stable extrusion molding becomes possible.

2. 2. Cooling roll (group) (B)
The cooling rolls (groups) of the present invention will be described below.
The cooling rolls (group) (B) of the present invention are installed behind the first cooling roll (A) arranged immediately after the die outlet. The cooling rolls (group) (B) of the present invention include one or more rolls. The cooling rolls (group) (B) of the present invention are equipment for cooling the resin sheet.

By cooling the resin sheet with the first cooling roll (A) and the cooling rolls (group) (B), both surfaces of the resin sheet can be sufficiently cooled even when the expansion ratio of the resin sheet increases. It will be possible. In addition, the appearance and smoothness of the sheet are improved, and a good foamed sheet having a low open cell ratio can be obtained.

The cooling rolls (group) (B) are placed behind the first cooling roll (A) placed immediately after the die. The cooling rolls (group) (B) are arranged in front of the take-up speed determination roll described later, which determines the take-up speed of the resin sheet.

The cooling rolls (group) (B) may be one roll or a plurality of rolls. It is preferable that the cooling rolls (group) (B) are provided with a mechanism capable of suitably adjusting the tension balance of the resin sheet before and after each cooling roll.

As described above, in the molding of the resin sheet, the volume of the sheet expands or contracts when the sheet is picked up. Therefore, when all the cooling rolls (groups) are driven at the same speed, the tension of the sheet becomes non-uniform before and after each cooling roll. In this case, the tension of the sheet becomes excessively large, and problems such as crushing of air bubbles, a decrease in the foaming ratio, and deterioration of the appearance of the sheet are likely to occur.

In particular, in order to produce a foamed sheet having a high foaming ratio, a low open cell ratio, and an excellent appearance, it is necessary to take the sheet before and after each cooling roll so that the tension of the sheet is not excessive. As this method, for example, a method of independently controlling the speed of each cooling roll while measuring the tension of the resin sheet before and after each cooling roll can be considered. However, when the number of cooling rolls is large, it is difficult to adjust the speed of each roll individually. Also, it takes a lot of time to adjust the speed of each roll. Further, every time the foaming state changes, it is necessary to fine-tune the roll speed. For this reason, it is practically difficult to easily obtain a good foam sheet.

As a method other than adjusting the speed of each roll individually, there is a method in which the cooling rolls (group) (B) are freely driven without providing an electric drive mechanism. By freely driving the cooling rolls (group) (B), the speed of the roll changes according to the volume change of the resin sheet, so that the tension of the resin sheet before and after the roll can be naturally adjusted. According to this method, the tension between each roll contained in the cooling rolls (group) (B) is local only by adjusting the speed of the first cooling roll (A) and the speed of the take-up speed determining roll. It can be prevented from becoming excessive. That is, where the volume of the resin sheet expands due to the foaming of the resin, the rotation of the cooling roll becomes faster in accordance with the expansion. On the contrary, where the volume of the resin sheet shrinks due to the cooling and solidification of the resin, the rotation of the cooling roll slows down in accordance with the shrinkage. By changing the speed of the roll in this way, the tension of the sheet is locally adjusted.

Another method is to control the torque of each cooling roll in order to adjust the tension of the sheet between the rolls. According to this method, all the cooling rolls can be rotated with an appropriate torque, and the tension of the resin sheet before and after the cooling rolls can be controlled.

A powder clutch or a hysteresis clutch can be provided to adjust the tension of the sheet between the rolls. This method is particularly preferably applicable when a large number of cooling rolls are provided in order to enhance the cooling of the sheet. When the number of cooling rolls is large, even when the cooling roll group (B) is driven freely, the resistance generated by the rotation of each cooling roll increases by the amount of the increase in the number of rolls. As a result, the tension of the sheet between each roll tends to increase. In such a case, it is more preferable to control the tension with a powder clutch or the like.

The cooling rolls (group) (B) include one or more cooling rolls, but the number is not limited. Any number of cooling rolls can be arranged according to the appearance of the resin sheet and the cooling state. For example, in the following cases (1) to (4), it is preferable to arrange a large number of cooling rolls (groups).
(1) The temperature of the discharged resin is high.
(2) High foaming ratio.
(3) The take-up speed of the resin sheet is high, and the contact time with one cooling roll is short.
(4) The thickness of the resin sheet is large.
In these cases, it is difficult to cool the resin sheet, so it is preferable to arrange more cooling rolls to enhance the cooling capacity.

The outer diameter of the cooling rolls (group) (B) is not particularly limited. An appropriate outer diameter can be selected according to the discharge amount of the resin, the cooling state, or the take-up speed. When two or more cooling rolls are arranged, the outer diameter of each cooling roll may be the same or different. If the outer diameter of the cooling rolls (group) (B) is too large, the rotational resistance of the rolls increases as described above. In this case, even when the roll is driven freely, the resin sheet is liable to be crushed or loosened. In addition, foaming defects are likely to occur. Further, the cooling of the surface not in contact with the roll is delayed, and the foaming property may be deteriorated. Therefore, the outer diameter of the cooling rolls (group) (B) is preferably 300 mm or less.

The structure of the cooling rolls (group) (B) is not particularly limited. It is desirable that the cooling rolls (group) (B) have a structure in which a cooling medium such as water is passed through the inside to control the temperature in order to stably cool the sheet. For example, the cooling rolls (group) (B) may have a single tube structure inside. In order to further improve the cooling efficiency, the cooling rolls (group) (B) may have a double pipe structure, a jacket structure, or the like.

The surface temperature of the cooling rolls (group) (B) is not particularly limited as long as it is a temperature suitable for cooling the resin sheet. The temperature of the cooling medium used for the cooling rolls (group) (B) is preferably 5 to 40 ° C. in order to sufficiently cool the sheet. If the temperature of the cooling medium used for the cooling rolls (group) (B) is too high, the resin is not sufficiently cooled, and the bubbles may become coarse. In addition, the bubbles may coalesce to increase the open cell ratio. In addition, corrugations may occur prominently. If the temperature of the cooling medium used for the cooling roll group (B) is too low, water is generated on the surface of the roll due to dew condensation, and this water may deteriorate the appearance of the sheet.

3. 3. Pick-up speed determination roll The take-back speed determination roll of the present invention will be described below.
The take-up speed determining roll of the present invention is a roll that determines the take-up speed of the resin sheet. The take-up speed determining roll is arranged behind the first cooling roll (A) and the cooling rolls (group) (B) described above. The take-up speed determination roll has a role of determining the take-back speed of the resin sheet.

As the take-up speed determining roll, for example, a general nip roll can be used. Alternatively, a roll having a suction mechanism and determining the take-up speed by sucking the resin sheet can be used.

When the equipment for picking up the resin sheet is provided with a plurality of nip rolls or suction rolls, the roll that first nip or suck the resin sheet behind the cooling rolls (group) (B) corresponds to the pick-up speed determining roll.

Examples of the configuration of the entire equipment for taking over the resin sheet are shown in FIGS. 1 to 4. The present invention is not limited to the configurations shown in FIGS. 1 to 4.

In the example shown in FIG. 1, the equipment for picking up the resin sheet S is a first cooling roll (A) arranged immediately after the outlet of the die 12 and a pick-up speed determining roll for determining the picking speed of the resin sheet S. A cooling roll (B) arranged between the 14 and the first cooling roll (A) and the take-up speed determining roll 14 is provided. In this example, the first cooling roll (A) has a drive mechanism. The cooling roll (B) does not have a drive mechanism and is free. The take-up speed determination roll 14 has a drive mechanism, and is a nip roll in which the resin sheet S can be sandwiched between a pair of upper and lower rolls.

In the example shown in FIG. 2, the equipment for picking up the resin sheet S is a first cooling roll (A) arranged immediately after the outlet of the die 12 and a pick-up speed determining roll for determining the picking speed of the resin sheet S. It is provided with 14 and two cooling roll groups (B) arranged between the first cooling roll (A) and the take-up speed determination roll 14. In this example, the first cooling roll (A) has a drive mechanism. The cooling roll group (B) does not have a drive mechanism and is free. The take-up speed determination roll 14 has a drive mechanism, and is a nip roll in which the resin sheet S can be sandwiched between a pair of upper and lower rolls.

In the example shown in FIG. 3, the equipment for picking up the resin sheet S is a first cooling roll (A) arranged immediately after the outlet of the die 12 and a pick-up speed determining roll for determining the picking speed of the resin sheet S. A group of four cooling rolls (B) arranged between the first cooling roll (A) and the take-up speed determining roll 14 is provided. In this example, the first cooling roll (A) has a drive mechanism. The cooling roll group (B) does not have a drive mechanism and is free. The take-up speed determination roll 14 has a drive mechanism, and is a nip roll in which the resin sheet S can be sandwiched between a pair of upper and lower rolls.
In the example shown in FIG. 3, the cooling roll group (B) may have a drive mechanism instead of a free roll. Further, the cooling roll group (B) may be a powder clutch roll having a drive mechanism.

In the example shown in FIG. 4, the equipment for picking up the resin sheet S is a first cooling roll (A) arranged immediately after the outlet of the die 12 and a pick-up speed determining roll for determining the picking speed of the resin sheet S. A group of four cooling rolls (B) arranged between the first cooling roll (A) and the take-up speed determining roll 14 is provided. In this example, the first cooling roll (A) has a drive mechanism. The cooling roll group (B) does not have a drive mechanism and is free. The take-up speed determination roll 14 has a drive mechanism, and is composed of a suction roll having a mechanism for sucking the resin sheet S. The resin sheet S picked up by the pick-up speed determining roll 14 is guided by two guide rolls 16.

The take-up speed determining roll has a drive mechanism different from that of the first cooling roll (A) described above. As a result, the take-up speed determination roll can be driven at a take-back speed different from that of the first cooling roll (A).

By adjusting the speed (ratio) of the first cooling roll (A) and the take-up speed determining roll, it is possible to adjust the tension generated in the resin sheet. By this adjustment, it is possible to suppress the crushing of air bubbles during molding of the resin sheet, particularly even when the foaming ratio is high. In addition, it is possible to achieve both good foaming characteristics and excellent appearance.

The specific adjustment method is as follows, for example.
When the speed of the take-up speed determining roll is made higher than the speed of the first cooling roll (A), a larger tension is generated in the resin sheet.
Adjusting the speed in the opposite direction reduces the tension of the resin sheet.

When the take-up speed of the resin sheet by the first cooling roll (A) is R1 and the take-up speed of the resin sheet by the take-back speed determining roll is R2, it is preferable to satisfy the following relationship.

R2 × 1.10 ≧ R1 ≧ R2 × 0.90
More preferably, R2 × 1.05 ≧ R1 ≧ R2 × 0.92

When the take-up speed of the resin sheet by the first cooling roll (A) is higher than the above range, wrinkles and slack are likely to occur in the resin sheet, and the appearance is deteriorated.

When the take-up speed of the resin sheet by the first cooling roll (A) is smaller than the above range, the tension generated in the resin sheet tends to be excessive. Further, when the resin sheet is molded, the foaming ratio is significantly reduced due to the crushing of air bubbles and the release of gas from the resin sheet. Further, as the gas escapes from the resin sheet, the surface of the sheet swells and then the portion is crushed by roll pressure bonding, so that the appearance is deteriorated (flame swelling phenomenon).

There are no particular restrictions on the outer diameter and shape of the take-up speed determination roll. The take-up speed determining roll preferably has an outer diameter and a shape capable of stably taking up the resin sheet.

The take-up speed determining roll is composed of, for example, a pair of upper and lower metal rolls. In this case, it is preferable that the take-up speed determining roll has a nip mechanism capable of sandwiching the resin sheet by moving one of the metal rolls up and down with an air or hydraulic cylinder. The take-up speed determining roll may be composed of a rubber roll having a similar mechanism. Alternatively, the take-up speed determining roll may be composed of a suction roll having a mechanism for sucking the resin sheet from the inner surface of the porous metal roll by a blower.

The take-up speed determination roll may have a function of determining the take-up speed of the resin sheet. The pick-up speed determination roll may also have other functions. For example, when the cooling capacity of the first cooling roll (A) and the cooling rolls (group) (B) is insufficient, the take-up speed determining roll may have a function for cooling the resin sheet.

4. Extruder The extruder of the present invention will be described below.
As the extruder for molding the resin sheet of the present invention, a general single-screw or twin-screw extruder having a T-die at the tip can be applied. Further, it is preferable to use an extruder having a sufficient resin cooling unit. “Sufficient resin cooling unit” means having a cooling unit having a screw length / screw diameter (L / D) of 10 or more.

As an example of such an extruder, an extruder having a single shaft, having a cooling zone having an L / D of 10 or more, and capable of cooling the resin in the cooling zone after the plasticization and kneading of the raw materials are completed. Can be mentioned.

Another example is an extruder that is a tandem type in which two extruders are connected, in which the first stage extruder plasticizes and kneads the raw material, and the second stage extruder cools the resin. be able to. This second stage extruder has a cooling zone with an L / D of 10 or more.

Another cooling facility may be provided between the extruder having a cooling section having an L / D of less than 10 and the die. An example of this cooling equipment is a static mixer whose temperature can be adjusted. In this case, it is preferable that the total length of the cooling unit and another cooling facility satisfies 10 or more in L / D.

In extrusion foam molding, it is important to adjust the temperature of the resin discharged from the die in order to adjust the viscosity of the molten resin to a range suitable for foaming. In particular, when the discharge amount of the extruder is large, the calorific value due to the shearing of the resin increases. When the calorific value increases, the resin temperature tends to rise, making it difficult to cool the resin. In such a case, as described above, it is preferable to use an extruder having a resin cooling zone having a higher capacity than usual.

5. Foamed Sheet The foamed sheet of the present invention will be described below.
The foamed sheet of the present invention may be a single layer or a multi-layered sheet. From the viewpoint of improving the appearance and thermoforming property, it is preferable to have multiple layers. Examples of multi-layers include:
Two-kind two-layer configuration such as non-foaming layer / foaming layer Two-kind three-layer configuration such as non-foaming layer / foaming layer / non-foaming layer

The foam sheet may be a multi-layer including another resin layer. Examples of such a multi-layer include the following.
Three-kind three-layer configuration such as non-foam layer / foam layer / other resin layer, three-kind five-layer configuration such as non-foam layer / foam layer / other resin layer / foam layer / non-foam layer

The foamed sheet may include a layer having a function according to the purpose. The foamed sheet may include, for example, a gas barrier layer and an impact resistant layer.

A printing layer, a decorative layer, or the like can be provided on the outside of the non-foamed layer as long as the effects of the present invention are not impaired. Further, for example, an adhesive layer can be provided between the layers.

The thickness of the foamed sheet of the present invention is not particularly limited. The thickness of the foamed sheet is preferably 0.3 mm to 5.0 mm, more preferably 0.5 mm to 4.0 mm, and even more preferably 0.5 mm to 3.5 mm. When the thickness of the foamed sheet is within this range, a foamed sheet having practical strength and excellent physical characteristics can be obtained. In addition, molding defects such as the resin sheet breaking at the bent portion during foam molding are unlikely to occur.

The surface of the foamed sheet of the present invention may be subjected to surface treatment such as corona discharge treatment, flame treatment, and plasma treatment in order to improve printability and paintability.

When the foamed sheet has a multi-layer structure including a non-foamed layer, the thickness of the non-foamed layer is preferably 0.1 to 50%, more preferably 0.1 to 20% of the total thickness of the multi-layer foamed sheet. When the thickness of the non-foamed layer is in this range, a foamed sheet having a good appearance and practical strength and light weight can be obtained.

The foaming ratio of the foamed layer contained in the foamed sheet is larger than 2.1 times, preferably 2.5 times or more, from the viewpoint of reducing the environmental load, light weight, and improving the heat insulating property. When the foaming ratio of the foamed layer is 2.1 times or less, the advantages of the foamed sheet such as light weight and heat insulating property are likely to be impaired.

The open cell ratio of the foam layer contained in the foam sheet is 20 Vol. From the viewpoint of good heat insulation and sheet characteristics. Must be lower than%. When the open cell ratio of the foam layer is 20 Vol.% Or more, defects are likely to occur during thermoforming. For example, defects such as air bubbles floating on the surface of the sheet during thermoforming are likely to occur. Alternatively, the surface of the sheet swells due to heating, and defects such as leaving marks on the surface of the sheet after molding are likely to occur. Further, when the open cell ratio of the foamed layer is 20 Vol.% Or more, the heat insulating property and rigidity of the foamed sheet may decrease.

6. Thermoplastic resin 6.1. Thermoplastic resin for foam layer The thermoplastic resin of the present invention will be described below.
The thermoplastic resin in the present invention is not particularly limited, and is generally used for polyolefin resins such as polyethylene and polypropylene, styrene resins, polyester resins, polyvinyl chloride resins, polycarbonates, polyamides, and acrylic resins. Resins can be used, and even if it is one of these, two or more of them can be used. Among them, it is preferable to use a polyolefin-based resin having high chemical resistance and light weight, and a polypropylene-based resin having heat resistance of 100 ° C. or higher and highly suitable for a wide range of applications is more preferable.

Since the polypropylene-based resin having crystallinity generally has a linear molecular structure and a standard molecular weight distribution, the melt tension is low and extrusion foam molding is difficult. By the production method of the present invention, a foaming ratio larger than 2.1 times can be obtained even when a linear polypropylene resin is used, but a polypropylene resin having a high melt tension and the production method of the present invention are combined. However, it is effective for obtaining a foamed sheet having a higher foaming ratio. Examples of polypropylene-based resins with high melt tension include polypropylene having an ultra-high molecular weight component by two-stage polymerization (see Tokusho 3-755562) and polypropylene-based resin obtained by a method of producing an ultra-high molecular weight polyethylene component by prepolymerization. A macromonomer having a terminal unsaturated bond is produced by polymerizing a monomer using a resin (see JP-A-2000-143858) and a metallocene catalyst having a specific structure, and the long chain is produced by copolymerizing it with propylene. Polypropylene produced by a method for forming a branch (see Patent No. 6171717, Patent No. 6232832, Patent No. 05027353, Patent No. 045539366) and polypropylene obtained by generating a radical and introducing a long-chain branch. (See Special Fairness 07-045551, Patent No. 0434715) and the like are exemplified. Among these, a polypropylene-based resin composition based on a specific long-chain branched polypropylene and a specific impact copolymer, which has a balance between melt tension and ductility suitable for extrusion foam molding, is preferable from the viewpoint of improving foaming characteristics.

Further, a filler may be added to the thermoplastic resin for the purpose of improving rigidity or the like. Typical examples are talc, calcium carbonate, silica, diatomaceous earth, alumina, titanium oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, calcium silicate, glass beads, bentonite, glass flakes, glass fiber, carbon fiber, aluminum powder. , Molybdenum sulfide, boron fiber, potassium titanate, calcium titanate, hydrotalcite, carbon fiber, pomegranate powder, mica, calcium phosphate, aluminum phosphate and other inorganic fillers, PMMA beads, cellulose fiber, polyamide fiber, Examples thereof include organic fillers such as aramid fiber, polyester fiber, paddy husk, wood flour, and kenaf fiber. Among these, the inorganic filler is preferable from the viewpoint of improving physical properties, handling, odor, and price, and has little influence on the foaming characteristics, and talc and calcium carbonate are preferable from the viewpoint of improving physical properties, price, and odor. The amount of these fillers added can be arbitrarily selected according to the desired physical characteristics.

Further, the thermoplastic resin of the present invention includes antioxidants, neutralizers, light stabilizers, ultraviolet absorbers, blocking inhibitors, lubricants, antistatic agents, metal deactivators, colorants, crystal nucleating agents and the like. Various additives can be blended within a range that does not impair the object of the present invention. The blending amount of these additives is not particularly limited, and an amount that exhibits the desired performance can be added. The blending amount of the additive is generally 0.0001 to 30% by weight, preferably 0.001 to 10% by weight.

6.2. Thermoplastic resin for non-foamed layer The thermoplastic resin used for the non-foamed layer when the foamed sheet has a multi-layer structure is not particularly limited, and a polyolefin resin such as polyethylene or polypropylene, a styrene resin, etc. General resins such as polyester resin, polyvinyl chloride resin, polycarbonate, polyamide, and acrylic resin can be used. One of these may be used, or two or more of them may be used. Above all, it is preferable to use a polyolefin resin having high chemical resistance and light weight.

Among the polyolefin resins, polypropylene and propylene-α-olefin copolymers are preferable from the viewpoints of recyclability, adhesiveness, heat resistance, oil resistance, rigidity, appearance and the like. The propylene-α-olefin copolymer includes an impact copolymer obtained by multi-step polymerization of a propylene (co) polymer and an ethylene-propylene random copolymer using a plurality of or single-tank polymerization tanks.

In order to improve the rigidity of the foamed sheet or the container made of the obtained foamed sheet, it is preferable to provide a non-foamed layer on the surface side of the foamed layer. In addition, an inorganic filler can be added to the non-foaming layer. When an inorganic filler is added to the non-foamed layer, the rigidity can be further effectively improved.

When the inorganic filler is blended in the non-foamed layer, it is desirable to blend 50 parts by weight or less of the inorganic filler with respect to 100 parts by weight of the thermoplastic resin used. If the amount of the inorganic filler compounded exceeds 50 parts by weight, shavings may occur at the outlet of the die and the appearance of the foamed sheet may be deteriorated. A non-foaming layer containing no inorganic filler may be provided on the surface of the non-foaming layer containing the inorganic filler. By further providing a non-foaming layer containing no inorganic filler, the appearance of the foamed sheet can be improved in addition to improving the rigidity of the foamed sheet.

Examples of preferable inorganic fillers contained in the non-foaming layer include talc, calcium carbonate, silica, hydrotalcite, zeolite, aluminum silicate, magnesium silicate and the like.

7. Method for Producing Foam Sheet The foam sheet of the present invention can be produced by using an extruder to which a T-die is connected. The method for producing a foamed sheet of the present invention includes an extrusion step of extruding a foamable resin sheet by an extruder equipped with a T-die, and a cooling step of cooling the resin sheet. In the extrusion step, for example, after kneading the thermoplastic resin and the foaming agent, the resin sheet is extruded from the T-die connected to the extruder. In the cooling step, for example, the resin sheet is taken up by the first cooling roll (A) arranged immediately after the T-die and the subsequent cooling rolls (group) (B). By taking over the resin sheet, the resin sheet is stretched while being cooled. At this time, the take-up speed of the resin sheet is determined by the above-mentioned take-up speed determination roll.

The foamed sheet of the present invention may be a multilayer foamed sheet. The multilayer foam sheet can be produced by general coextrusion molding. Specifically, the foamed layer and the non-foamed layer made of a thermoplastic resin can be simultaneously molded by coextrusion molding. For example, it is possible to form a multilayer foam sheet by using a plurality of extruders equipped with a feed block and a multi-die. The multi-layer foam sheet can have various layer configurations described above. The non-foamed layer may be provided on any surface of the foamed layer. The multilayer foamed sheet may have a structure (sandwich structure) in which a foamed layer exists between two non-foamed layers.

The type of foaming agent used in producing the foam sheet is not particularly limited, and a known foaming agent used for plastics, rubbers and the like can be used. Further, microcapsules containing a physical foaming agent, a decomposable foaming agent (chemical foaming agent), a thermal expansion agent and the like can be used. One of these may be used, or a plurality of types may be used in combination.

Specific examples of the physical foaming agent include aliphatic hydrocarbons such as propane, butane, pentane and hexane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane and dichloro. Difluoromethane, chloromethane, dichloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, trichlorotrifluoroethane, dichlorotetrafluoroethane , Halogenized hydrocarbons such as chloropentafluoroethane and perfluorocyclobutane, inorganic gases such as water, carbon dioxide, and nitrogen, and the like can be exemplified. These compounds may be used alone or in combination of a plurality of compounds.

Of these, aliphatic hydrocarbon gases such as propane, butane, and pentane, and carbon dioxide are preferable because they are inexpensive and have high solubility in polypropylene resins. When carbon dioxide gas is used, supercritical conditions of 7.4 MPa or more and 31 ° C. or higher are more preferable because they are in a state of excellent diffusion and solubility in the resin.

Specific examples of the degradable foaming agent (chemical foaming agent) include a mixture of sodium bicarbonate and an organic acid such as citric acid, an azo foaming agent such as azodicarboxylic amide and barium azodicarboxylic acid, and N, N'-dinitrosopentamethylene. Nitroso-based foaming agents such as tetramine, N, N'-dimethyl-N, N'-dinitrosoterephthalamide, sulfohydrazide-based foaming agents such as p, p'-oxybisbenzenesulfonyl hydrazide, p-toluenesulfonyl semicarbazide, tri Hydrazinotriazine and the like can be mentioned. The blending amount of the foaming agent is preferably in the range of 0.05 to 10 parts by weight with respect to 100 parts by weight of the polypropylene-based resin composition constituting the foam layer.

When a physical foaming agent is used, a bubble adjusting agent can be used, if necessary. By adding the bubble adjusting agent, the number of bubble nuclei generated can be increased even under the same molding conditions, so that the desired bubble diameter can be adjusted. Examples of bubble conditioners include inorganic degradable foaming agents such as ammonium carbonate, baking soda, ammonium bicarbonate and ammonium nitrite, azo compounds such as azodicarboxylic amide, azobisisobutyronitrile and diazoaminobenzene, N and N. ′ -Dinitrosopentane methylenetetramine and nitroso compounds such as N, N'-dimethyl-N, N'-dinitrosoterephthalamide, benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p, p'-oxybisbenzenesulfonyl semicarbadide, Degradable foaming agents such as p-toluenesulfonyl semicarbadide, trihydrazinotriazine, bariumazodicarboxylate, inorganic powders such as talc and silica, acidic salts such as polyvalent carboxylic acid, polyvalent carboxylic acid and sodium carbonate or sodium bicarbonate. The reaction mixture of the above can be exemplified. These bubble modifiers may be used alone or in combination of two or more.

If the blending amount of the bubble adjusting agent is too small, the bubbles cannot be sufficiently refined, and it becomes difficult to adjust the bubble diameter. If the blending amount of the bubble adjusting agent is too large, the bubbles are excessively finely divided, so that the formation of open cells is promoted, the gas escape becomes remarkable, and as a result, foaming defects are likely to occur. For this reason, the blending amount of the bubble modifier is preferably in the range of 0.005 to 5 parts by weight in terms of pure content with respect to 100 parts by weight of the polypropylene resin composition for the foam layer. The term "pure content" as used herein means, for example, the amount of an effective component as a bubble adjusting agent contained in the master batch when a master batch is used as the bubble adjusting agent.

8. Applications The foamed sheet manufactured by the manufacturing method of the present invention has a high foaming ratio, an excellent appearance, and a light weight. Therefore, the foamed sheet manufactured by the manufacturing method of the present invention can be used for foamed food containers such as trays, cups, plates and cups, vehicle interior materials such as automobile door trims and automobile trunk mats, building materials, heat insulating materials, packaging, stationery and the like. It is preferably applicable.

In addition, the foamed sheet produced by the production method of the present invention has a high closed cell ratio and is also excellent in thermoformability. The term "thermoforming" as used herein generally means that a heat-softened plastic sheet is pressed against a desired mold for molding. An example of thermoforming is vacuum forming, in which air in the gap between the mold and the material is removed and the material is brought into close contact with the mold by atmospheric pressure. Further, as another example, there are pressure-pneumatic molding in which compressed air of atmospheric pressure or higher is used for molding, and vacuum pressure-pneumatic molding in which vacuum and pressure air are used in combination. Further, as another example, after arranging the sheet in a space larger than the thickness of the sheet provided between the mold having a concave shape and the mold having a convex shape, the sheet is evacuated from both sides of the mold. Double-sided vacuum forming to be performed.

The thermoforming method is not particularly limited, and for example, methods such as plug molding, match molding, and plug assist molding can be exemplified.

[Evaluation methods]
In Examples and Comparative Examples, the physical properties of the polypropylene resin, the multilayer foamed sheet, and the constituents thereof were measured and evaluated according to the following evaluation methods.
(1) MFR
The MFR complies with JIS K7210: 1999 "Plastics-Test Method for Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastics", Method A, Condition M (230 ° C, 2.16 kg load). Was measured.

(2) Apparent density and foaming ratio of the foamed layer A test piece was cut out from the foamed sheet according to JIS K7222. The apparent density of the foamed sheet was determined by dividing the weight (g) of the test piece by the volume (cm ³ ) obtained from the external dimensions of the test piece.

Next, a cross section in the width direction of the foam sheet was observed using an optical microscope equipped with a CCD camera, and an observation image was taken at a magnification of 5 times. Using the LAS image analysis software manufactured by Leica, the thickness of each of the target non-foamed layer and the foamed layer was measured at 5 points for each layer, and the average value was taken as the thickness of each layer. The apparent density of the foamed layer of the foamed sheet was calculated from the apparent density of the foamed sheet, the thickness of each of the foamed layer and the non-foamed layer, and the density of each layer. The density of the polypropylene resin used for the calculation 0.91 g / cm ^3, the density of a 50:50 mixture of PPF-1 and PP-5 used for the PP filler layer in the examples is 1.15 g / cm ³ ..

Further, the expansion ratio of the foamed layer was calculated by dividing the density of the polypropylene resin of 0.91 g / cm ³ by the apparent density of the foamed layer.
For the foamed sheet on which the non-foamed layer was not laminated, the foaming ratio of the foamed layer was calculated by dividing the polypropylene resin density of 0.91 g / cm ³ by the apparent density of the foamed sheet.

(3) Open cell ratio of foam sheet A test piece was cut out from the foam sheet. Using an air pycnometer (manufactured by Tokyo Science Co., Ltd.), the open cell ratio of the cut out test piece was measured according to the method described in ASTM D2856.

(4) Appearance evaluation of foamed sheet The appearance of the surface of the foamed sheet was evaluated. Specifically, the foam sheets obtained in each Example and each Comparative Example were visually evaluated according to the following criteria.
⊚: The surface of the foamed sheet is smooth with no visible unevenness.
◯: On the surface of the foamed sheet, slight unevenness due to air bubbles is visually observed, but no wrinkles or swelling are confirmed.
X: On the surface of the foamed sheet, poor appearance due to unevenness, wrinkles, or swelling is confirmed.

(5) Thermoforming property of foam sheet The foam sheet obtained in Examples and Comparative Examples is cut into 53 cm × 53 cm, and a container is vacuum-formed using a multipurpose thermoforming machine (manufactured by Asano Laboratories Co., Ltd.). Molded.
The procedure of vacuum forming is as follows. First, the above-mentioned cut foam sheet was set in the clamp frame. Next, after heating both sides of the foam sheet with the upper and lower heaters, the container was molded by vacuum compressed air molding using a circular container mold having an inner diameter of 22 cm and a depth of 3.8 cm at the upper part.

The molded container was visually evaluated according to the following criteria. When molding each sample, the heating time and the position of the mold were adjusted so that the container could be molded as clean as possible.
◯: No wrinkles or crushes were confirmed in the container after thermoforming, and a good container could be molded.
Δ: Slight wrinkles and crushing were confirmed on the container after thermoforming, but the container could be molded.
X: Significant crushing and wrinkles were confirmed in the container after thermoforming, and a good container could not be molded.

[Material used]
The following polypropylene resins PP-1 to PP-5 were used.
<Resin for foam layer>
(PP-1)
BC3HF (MFR = 6.2 g / 10 minutes) manufactured by Japan Polypropylene Corporation was used as PP-1. From ¹³ C-NMR measurement of PP-1, it was confirmed that there was no long chain branch in this polypropylene.
(PP-2)
As PP-2, WAYMAX EX4000 (MFR = 8.5 g / 10 minutes) manufactured by Japan Polypropylene Corporation, which has high strain curability, was used. From ¹³ C-NMR measurement of PP-2, it was confirmed that this polypropylene had a long chain branch.
(PP-3)
As PP-3, MA1B (MFR = 20.0 g / 10 minutes, MT = 4.2 g) manufactured by Japan Polypropylene Corporation was used. From ¹³ C-NMR measurement of PP-3, it was confirmed that there was no long chain branch in this polypropylene.
(PP-4)
As PP-4, WAYMAX EX6000 (MFR = 2.5 g / 10 minutes) manufactured by Japan Polypropylene Corporation, which has high strain curability, was used. From ¹³ C-NMR measurement of PP-4, it was confirmed that this polypropylene had a long chain branch.

<Resin for non-foamed layer>
(PP-5)
As PP-5, BC3BRF (MFR = 12 g / 10 minutes) manufactured by Japan Polypropylene Corporation was used.

<Resin for PP filler layer>
(PPF-1)
As PPF-1, a talc masterbatch TX1447MBN manufactured by Japan Polypropylene Corporation and BC3BRF (MFR = 12 g / 10 minutes) manufactured by Japan Polypropylene Corporation were dry-blended at a ratio of 50:50.

[Example 1]
1) Raw materials used The following materials were used as the polypropylene resin for the foam layer, the bubble conditioner, and the polypropylene resin for the non-foam layer.
-Polypropylene resin for foam layer: PP-1
-Polypropylene resin for non-foamed layer: PP-5
・ Bubble conditioner: Chemical foaming agent manufactured by Clariant Japan Co., Ltd. (trade name: Hydrocerol CF40E-J)

2) Manufacture of multi-layer foam sheet by T-die extrusion foam A multi-layer foam sheet was manufactured as follows.
2-1) A raw material was prepared by dry-blending 0.5 parts by weight of the above bubble adjusting agent with 100 parts by weight of polypropylene resin PP-1 for a foam layer. The prepared raw material was put into the raw material supply hopper of the single-screw extruder A. Carbon dioxide gas boosted by a high-pressure pump was injected as a physical foaming agent from an injection port opened in the cylinder of the extruder. While injecting carbon dioxide gas, the molten raw material was extruded from a T-die having a width of 750 mm and a lip gap of 0.4 mm via a feed block to form a resin sheet. At this time, the non-foamed layer was formed by co-extruding the resin PP-5 for the non-foamed layer using two single-screw extruders B and C for the non-foamed layer. A non-foamed layer was laminated on both surfaces of the foamed layer with a feed block to produce a multi-layer foamed sheet of 2 types and 3 layers.

The operating conditions of each extruder, the functions of each part of the extruder cylinder for the foam layer, and other molding conditions are as follows.

・ Single shaft extruder A (foam layer)
Diameter 65 mm, L / D = 50, carbon dioxide injection port is located between C4-C5 Introduced gas amount: 0.20 kg / h
Screw rotation speed: 75 rpm
Discharge rate: Approximately 65 kg / h
Extruder set temperature:
C1: 180 ° C
C2 to C4 (plasticization of resin, decomposition of bubble modifier): 240 ° C.
C5 (resin cooling, dispersion of physical foaming agent): 190 ° C
C6 to C9 (resin cooling, dispersion of physical foaming agent): 175 ° C
SC1, SC2 (screen changer, resin cooling): 180 ° C
H (head part, resin cooling): 180 ° C

・ Single-screw extruders B and C (non-foaming layer)
Caliber 40 mm, L / D = 32
Screw rotation speed: 50 rpm
Discharge rate: Approximately 5 kg / h
Preset temperature:
C1: 180 ° C
C2: 230 ° C
C3: 190 ° C
C4: 180 ° C
AD1, AD2: 180 ° C

・ Die feed block temperature from the confluence: 175 ℃
Die temperature: 175 ° C

・ Cooling roll specifications Number of cooling rolls: 5
First cooling roll specification: Roll diameter 60 mmΦ, with drive mechanism First cooling roll speed: 2.80 m / min
2nd to 5th cooling roll specifications: Roll diameter 100 mmΦ, no drive mechanism Cooling roll temperature (5 rolls): 15 ° C

・ Pick-up speed: 2.90 m / min

In extrusion foam molding using a T-die, it is important to adjust the tension of the sheet before and after each cooling roll so that excessive tension is not generated in order to obtain good foaming characteristics. In this embodiment, the tension of the sheet before and after the first cooling roll was adjusted by the speed ratio between the first cooling roll and the take-up speed determining roll. Further, the tension of the sheets before and after the second to fifth cooling rolls is automatically adjusted because each cooling roll is a free roll having no electric drive mechanism. The tension of the sheet before and after each cooling roll was confirmed by the tension of the resin sheet. That is, when the tension of the resin sheet before and after each cooling roll is about the same, it is judged that the tension adjustment of the sheet is good.

Table 1 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

[Comparative Example 1]
A multilayer foam sheet was produced in the same manner as in Example 1 except that the speed of the first cooling roll was 2.21 m / min and the take-up speed was 2.60 m / min. Table 2 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet. In this comparative example, the ratio of the speed of the first cooling roll to the take-up speed was excessively small, so that the tension of the resin sheet taken up between the first cooling roll and the second cooling roll became excessively high. Therefore, the tension of the resin sheet was stronger than that of Example 1. As a result, the open cell ratio increased, the foaming ratio decreased, and the appearance and thermoformability of the foamed sheet decreased.

[Example 2]
PP-2 was used as the polypropylene resin for the foam layer. The same bubble adjusting agent as in Example 1 was used. These were mixed in the same ratio as in Example 1 to prepare a raw material. Using the prepared raw materials, a single-layer foamed sheet was produced under the following conditions.
Introduced gas amount: 0.27 kg / h,
Speed of the first cooling roll: 4.40 m / min,
Pick-up speed: 4.60 m / min

In Example 2, a single-layer foam sheet was produced in the same manner as in Example 1 except that a single-screw extruder for a non-foam layer was not used. Table 1 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

[Example 3]
PP-2 was used as the polypropylene resin for the foam layer. The same bubble regulator and polypropylene resin for the non-foaming layer as in Example 1 were used. A two-kind three-layer foam sheet was produced under the following conditions.
Introduced gas amount: 0.27 kg / h,
First cooling roll speed: 4.50 m / min,
Pick-up speed: 4.70 m / min

In Example 3, a two-kind three-layer foam sheet was produced under the same conditions as in Example 1 except for the above. Table 1 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

[Example 4]
A two-kind three-layer foam sheet was produced under the same conditions as in Example 3 except that the speed of the first cooling roll was set to 4.80 m / min. Table 1 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

[Example 5]
A two-kind three-layer foamed sheet was produced under the same conditions as in Example 3 except that the speed of the first cooling roll was 3.25 m / min and the take-up speed was 3.50 m / min. Table 1 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

[Example 6]
As the resin for the foam layer, a resin obtained by dry-blending PP-2 and PP-3 at a ratio of 50:50 (weight ratio) was used. The speed of the first cooling roll was set to 7.45 m / min, and the take-up speed was set to 7.30 m / min. Except for these conditions, a multilayer foamed sheet was produced by T-die extrusion foaming in the same manner as in Example 3. The evaluation results of the obtained multilayer foamed sheet are shown in Table 1.

[Comparative Example 2]
A multilayer foamed sheet was produced in the same manner as in Example 3 except that the speed of the first cooling roll was 4.00 m / min and the take-up speed was 4.70 m / min. Table 2 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

In this comparative example, the ratio of the speed of the first cooling roll to the take-up speed was excessively small, so that the tension of the resin sheet taken up between the first cooling roll and the second cooling roll became excessively high. Therefore, the tension of the resin sheet was stronger than that of Example 1. As a result, the open cell ratio increased, the foaming ratio decreased, and the appearance and thermoformability of the foamed sheet decreased.

[Comparative Example 3]
A multilayer foam sheet was produced in the same manner as in Example 3 except that a free roll having no drive mechanism was used as the first cooling roll. Table 2 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

When a plurality of free rolls having no drive mechanism are arranged in front of the take-up rolls, the load required to rotate each free roll increases as the number of rolls increases. In addition, the tension at the time of picking up the resin sheet cannot be controlled by changing the difference between the speed of the first cooling roll and the picking speed. As a result, it was confirmed that the tension applied to the resin sheet became excessive, the open cell ratio increased, and the appearance and thermoformability deteriorated.

[Comparative Example 4]
A multilayer foamed sheet was produced in the same manner as in Example 3 except that the speed of the first cooling roll was set to 5.52 m / min. Table 2 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet.

In this comparative example, since the ratio of the speed of the first cooling roll to the take-up speed was too large, the tension when taking over the sheet became too small, the resin sheet was loosened, and wrinkles remained. In addition, the tension applied to the resin sheet became too small, resulting in poor adhesion between the resin sheet and the cooling roll. As a result, the resin sheet was not sufficiently cooled, the open cell ratio increased, and the appearance and thermoformability of the foamed sheet deteriorated.

[Example 7]
1) Raw materials used The following materials were used as the polypropylene resin for the foam layer, the bubble conditioner, and the polypropylene resin for the non-foam layer.
-Polypropylene resin for foam layer: PP-2
-Resin for PP filler layer: 50:50 (weight ratio) dry blend mixture of PPF-1 and PP-5-Polypropylene resin for non-foamed layer: PP-5
・ Bubble conditioner: Chemical foaming agent manufactured by Clariant Japan Co., Ltd. (trade name: Hydrocerol CF40E-J)

2) Manufacture of multi-layer foam sheet by T-die extrusion foam A multi-layer foam sheet was manufactured as follows.
2-1) A raw material was prepared by dry-blending 0.5 parts by weight of the above bubble adjusting agent with 100 parts by weight of polypropylene resin PP-2 for a foam layer. The prepared raw material was put into the raw material supply hopper of the single-screw extruder A. Carbon dioxide gas boosted by a high-pressure pump was injected as a physical foaming agent from an injection port opened in the cylinder of the extruder. While injecting carbon dioxide gas, the molten raw material was extruded from a T-die having a width of 750 mm and a lip gap of 0.4 mm via a feed block to form a resin sheet.
At this time, the dry blend mixture of PPF-1 and PP-5 was supplied to the single-screw extruder B (diameter 65 mmφ) for the PPF layer. Further, the non-foamed layer was formed by co-extruding the resin PP-5 for the non-foamed layer using two single-screw extruders C and D for the non-foamed layer. A non-foamed layer, a PPF layer, and a foamed layer were laminated in a feed block. As a result, a multi-layer foamed sheet of 3 types and 5 layers having a layer structure of non-foamed layer / PPF layer / foamed layer / PPF layer / non-foamed layer was obtained. Table 1 shows the evaluation results of the obtained 3 types and 5 layer foam sheets.

The operating conditions of each extruder, the functions of each part of the extruder cylinder for the foam layer, and other molding conditions are as follows.

・ Single shaft extruder A (foam layer)
Diameter 65 mm, L / D = 50, carbon dioxide injection port is located between C4-C5 Introduced gas amount: 0.18 kg / h
Screw rotation speed: 75 rpm
Discharge rate: Approximately 65 kg / h
Extruder set temperature:
C1: 180 ° C
C2 to C4 (plasticization of resin, decomposition of bubble modifier): 240 ° C.
C5 (resin cooling, dispersion of physical foaming agent): 190 ° C
C6 to C9 (resin cooling, dispersion of physical foaming agent): 175 ° C
SC1, SC2 (screen changer, resin cooling): 180 ° C
H (head part, resin cooling): 180 ° C

・ Single shaft extruder B (PPF layer)
Caliber 65 mm, L / D = 28
Screw rotation speed: 50 rpm
Discharge rate: Approximately 40 kg / h
Extruder set temperature:
C1: 180 ° C
C2: 230 ° C
C3: 200 ° C
C4: 180 ° C
SC1, SC2: 180 ° C
AD1, AD2: 180 ° C

・ Single-screw extruders C and D (non-foaming layer)
Caliber 40 mm, L / D = 32
Screw rotation speed: 50 rpm
Discharge rate: Approximately 5 kg / h
Preset temperature:
C1: 180 ° C
C2: 230 ° C
C3: 190 ° C
C4: 180 ° C
AD1, AD2: 180 ° C

・ Die feed block temperature from the confluence: 175 ℃
Die temperature: 175 ° C

・ Cooling roll specifications Number of cooling rolls: 5
First cooling roll specification: Roll diameter 60 mmΦ, with drive mechanism First cooling roll speed: 8.42 m / min
2nd to 5th cooling roll specifications: Roll diameter 100 mmΦ, no drive mechanism Cooling roll temperature (5 rolls): 15 ° C

・ Pick-up speed: 8.78 m / min

[Comparative Example 5]
A multilayer foamed sheet was produced in the same manner as in Example 7 except that the first cooling roll speed was set to 7.65 m / min. Table 2 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet. In this comparative example, since the ratio of the speed of the first cooling roll to the take-up speed is too small, the tension between the first cooling roll and the second cooling roll when taking over the resin sheet becomes too large, and the tension of the sheet becomes too large. The condition was also stronger than that of Example 7. As a result, the open cell ratio deteriorated. In addition, a decrease in thermoformability was confirmed.

[Example 8]
The first cooling roll speed was 4.58 m / min, the take-up speed was 4.72 m / min, and T-die extrusion foaming was performed in the same manner as in Example 7 except that the thickness ratio of each layer was changed. I got a sheet. Table 1 shows the evaluation results of the obtained multilayer foamed sheet.

[Comparative Example 6]
A multilayer foamed sheet was produced in the same manner as in Example 8 except that the first cooling roll speed was 4.15 m / min. Table 2 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet. In this comparative example, since the ratio of the speed of the first cooling roll to the take-up speed is too small, the tension between the first cooling roll and the second cooling roll when taking over the resin sheet becomes too high, and the tension of the sheet becomes too high. The condition was also stronger than that of Example 8. As a result, the open cell ratio deteriorated. In addition, the foaming ratio decreased and the thermoformability decreased.

[Comparative Example 7]
A multilayer foam sheet was produced in the same manner as in Example 8 except that the first cooling roll speed was set to 5.30 m / min. Table 2 shows the results of evaluation of the characteristics, appearance, and thermoformability of the obtained foamed sheet. In this comparative example, since the ratio of the speed of the first small-diameter roll to the pick-up speed became too large, the tension when picking up the sheet became too small, the resin sheet was loosened, and wrinkles remained. Further, since the tension applied to the sheet became too small, the sheet and the cooling roll did not sufficiently adhere to each other, and the sheet was not sufficiently cooled. In addition, the open cell ratio deteriorated, the appearance deteriorated, and the thermoformability deteriorated.

[Example 9]
1) Raw materials used The following materials were used as the polypropylene resin for the foam layer and the chemical foaming agent.
-Polypropylene resin for foam layer: PP-4
-Chemical foaming agent: Chemical foaming agent manufactured by Clariant Japan Co., Ltd. (trade name: Hydrocerol CF40E-J)

2) Manufacture of foamed sheet by T-die extrusion foaming An extruded foamed sheet was manufactured as follows.
2-1) A raw material was prepared by dry-blending 5.0 parts by weight of the above chemical foaming agent with 100 parts by weight of polypropylene resin PP-4 for a foam layer. The prepared raw material was put into the supply hopper of the single-screw extruder A. The molten raw material was extruded from a T-die having a width of 150 mm and a lip gap of 0.4 mm via a feed block to form a single-layer resin sheet. A single-layer foamed sheet was produced by cooling the resin sheet.
The evaluation results of the obtained single-layer foamed sheet are shown in Table 3.

The operating conditions of the extruder and other molding conditions are as follows.
・ Single shaft extruder A (foam layer)
Caliber 30 mm, L / D = 32
Screw rotation speed: 40 rpm
Discharge rate: Approximately 4 kg / h
Extruder set temperature:
C1-C3: 230 ° C
C4-AD: 185 ° C
Die temperature: 185 ° C

・ Cooling roll specifications Number of cooling rolls: 3
First cooling roll specification: Roll diameter 50 mmΦ, with drive mechanism First cooling roll speed: 1.00 m / min
2nd to 3rd cooling roll specifications: Roll diameter 100mmΦ, with drive mechanism, with powder clutch Powder clutch torque setting: 4%
Cooling roll temperature (3 rolls): 50 ° C

・ Pick-up speed: 1.00 m / min

[Example 10]
T-die extrusion foaming was performed in the same manner as in Example 9 except that the powder clutch torque was set to 7% to obtain a single-layer foamed sheet. The evaluation results of the obtained single-layer foamed sheet are shown in Table 3.

[Example 11]
PP-2 is used for the polypropylene resin composition for the foam layer, the amount of the chemical foaming agent added is 6.5 parts by weight, the extruder rotation speed is 60 rpm (discharge amount: about 6 kg / h), and the first cooling roll speed. A single-layer foamed sheet was obtained by T-die extrusion foaming in the same manner as in Example 9 except that the take-up speed was 1.50 m / min and the powder clutch torque was set to 5%. The evaluation results of the obtained single-layer foamed sheet are shown in Table 3.

[Example 12]
PP-2 is used for the polypropylene resin for the foam layer, the amount of the chemical foaming agent added is 6.5 parts by weight, the extruder rotation speed is 60 rpm (discharge amount: about 6 kg / h), the first cooling roll speed and the take-up speed. A single-layer foamed sheet was obtained by T-die extrusion foaming in the same manner as in Example 9, except that both were 1.50 m / min and the powder clutch torque was set to 10%. The evaluation results of the obtained single-layer foamed sheet are shown in Table 3.

[Example 13]
PP-2 is used for the polypropylene resin for the foam layer, the amount of the chemical foaming agent added is 6.5 parts by weight, the extruder rotation speed is 60 rpm (discharge amount: about 6 kg / h), the first cooling roll speed and the take-up speed. A single-layer foamed sheet was obtained by T-die extrusion foaming in the same manner as in Example 9, except that both were 1.50 m / min and the powder clutch torque was set to 15%. The evaluation results of the obtained single-layer foamed sheet are shown in Table 3.

[Comparative Example 8]
A single-layer foamed sheet was obtained by T-die extrusion foaming in the same manner as in Example 9 except that the first cooling roll speed was 0.87 m / min and the powder clutch torque setting was 0%. In this comparative example, since the ratio of the speed of the first cooling roll to the take-up speed is too small, the tension between the first cooling roll and the second cooling roll when taking over the resin sheet becomes too large, and the tension of the sheet becomes too large. The condition was also stronger than that of Example 9. The evaluation results of the obtained single-layer foamed sheet are shown in Table 4.

[Comparative Example 9]
PP-2 is used for the polypropylene resin for the foam layer, the amount of the chemical foaming agent added is 6.5 parts by weight, the extruder rotation speed is 60 rpm (discharge amount: about 6 kg / h), and the first cooling roll speed is 1. A single-layer foamed sheet was obtained by T-die extrusion foaming in the same manner as in Example 9 except that the take-up speed was set to 32 m / min, the take-up speed was set to 1.50 m / min, and the powder clutch torque was set to 0%. The evaluation results of the obtained single-layer foamed sheet are shown in Table 4.

Claims (3)

A method for manufacturing a foam sheet made of a thermoplastic resin.
The foamed sheet has a foaming ratio greater than 2.1 times and 20 Vol. Contains a foam layer with an open cell ratio of less than%
A method for manufacturing a foamed sheet, which comprises an extrusion step of extruding a foamable resin sheet by an extruder equipped with a T-die and a cooling step of cooling the resin sheet.
In the cooling step, the first cooling roll (A) having a drive mechanism, which is arranged immediately after the die outlet, and the first cooling roll (A), which is arranged behind the first cooling roll, determines the take-up speed of the resin sheet. The resin sheet is cooled by one or more cooling rolls (groups) (B) arranged between the roll and the first cooling roll and the take-up speed determination roll, and the tension of the resin sheet does not become excessive. A method for manufacturing a foamed sheet, which comprises taking over a resin sheet in a state. When the take-up speed of the resin sheet by the first cooling roll (A) is R1 and the take-up speed of the resin sheet by the take-back speed determination roll is R2, the relationship of R2 × 1.10 ≧ R1 ≧ R2 × 0.90 is satisfied. , The method for producing a foam sheet according to claim 1. The method for producing a foam sheet according to claim 1 or 2, wherein the outer diameter of the first cooling roll (A) is 300 mm or less.

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