JPH074828B2 - Method and apparatus for manufacturing polyolefin resin crosslinked foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a manufacturing method and a manufacturing apparatus of a polyolefin resin crosslinked foam for non-contact and free foaming by heating.

(Prior Art and Problems) As a method for producing a crosslinked foamed polyolefin resin, a rigid foaming method and a horizontal foaming method are known, which are roughly classified according to the transport direction when foaming of a foamable resin composition sheet occurs.

As the rigid foaming method, for example, in Japanese Examined Patent Publication No. Sho 55-48974, a foamable resin composition sheet is transferred horizontally in a preheating chamber in a heating furnace, and after preheating, the sheet is provided vertically. There is disclosed a method of hanging in a heating foaming chamber and performing heating foaming in a non-contact manner. In the rigid foaming method, non-contact free width foaming is performed in heated air, so it is possible to obtain a smooth and beautiful foam with no scratches or irregularities on the surface and a good appearance, but due to the weight of the sheet during heat foaming. Since a large amount of tension is applied, there is a drawback that the molding strain remaining in the foamed sheet is large, and the difference in the residual strain in the flow direction and the width direction is large. Reducing such residual strain and ensuring uniformity in the width and flow directions stabilizes the dimensions during heating or heat drawdown during thermoforming (vacuum, pressure chamber, press molding, etc.). This is an important technical problem in order to make the resin uniform and to prevent wrinkles and the like, but the known rigid foaming method cannot sufficiently deal with it.

As a horizontal foaming method, for example, Japanese Examined Patent Publication No. 52-18232 discloses a method in which a foamable resin composition sheet is supported on a transfer belt made of a wire mesh and heated and foamed in a heating furnace. According to this method, the tension applied to the foam is small, so the molding strain is small, but since foaming is performed on the support, there are scratches and irregularities on the foam surface, and there are differences between the front and back of the foam. However, it is extremely difficult to obtain a foam having a good appearance.

Further, as a horizontal foaming method, Japanese Examined Patent Publication (Kokoku) No. Sho 43-22674, a foaming resin composition sheet is supported by a supporting belt in a preheating stage in a heating furnace, and is separated from the belt immediately before or after the start of foaming to be in a free state. Alternatively, a method of foaming in a state close to that is disclosed. In this method, unlike the method of heating and foaming on the supporting belt, the occurrence of scratches, front and back differences, etc. is considerably improved, but the foamable resin composition sheet and the supporting belt are in a melt-bonded state by heating. , Detachment from the belt does not occur smoothly, and scratches or irregularities may occur. Moreover, since the transfer to the heat-foaming stage depends only on the tension for pulling the foamed sheet, it cannot be said that the tension applied to the foam is sufficiently small, and in particular, the residual molding strain in the flow direction becomes large.

Japanese Patent Publication No. 42-10749 discloses a method in which a foamable resin composition sheet is floated on a liquid bath heated to a foaming temperature for heat foaming. According to this method, the residual molding strain can be reduced, but since a heated liquid or a residue floating on the liquid adheres to the foam, a treatment step for cleaning the foam is required, and at the time of foaming. Since the medium that comes in contact with the liquid is different from that of the gas on the front and back sides, the foam has a difference in appearance.

(Problems to be Solved by the Invention) As a result of research to overcome the problems of the above-described conventional techniques, the present inventors have found that a foamable polyolefin-based resin composition sheet is used in a foaming furnace such as a belt conveyor. On the air float bed with the hot air discharge porous membrane placed in the heating and foaming zone after the preheated sheet is transferred from the transfer device and preheated, and then the preheated sheet is released from the transfer device by blowing air from the release air nozzle. In addition, it is possible to smoothly separate the sheet from the transfer device by heating and free-foaming without blowing while blowing it up with hot air, and a transfer driving force is applied to the foamable resin composition sheet, which is applied to the foam. It was found that the tension can be significantly reduced and the residual strain and the strain difference between the width direction and the flow direction can be minimized.

Further, a glass fiber cloth coated with a polytetrafluoroethylene resin, by using a tilted air float bed having a porous film for hot air discharge adjusted air permeability, without causing any degree of foaming unevenness, A foam with a uniform degree of foaming can always be obtained, and further, there is no clogging of the porous membrane,
It has been found that foam molding can be performed under constant conditions even after long-term operation.

As described above, it is possible to provide a cross-linked foam having a smooth appearance, a uniform degree of foaming, and no molding residual strain.
It has become possible to overcome the drawbacks of the rigid foaming method and the horizontal foaming method and to bring out the advantages of both. However, in this method, since the foam is freely foamed in the air float state, there is no one that regulates the width of the foam, and the width of the foam that is obtained varies due to variations and distortions in the molding step of the expandable resin composition sheet. To do. Also, due to the air flow of the air float in the foaming stage, the sheet in the foaming process slightly moves left and right, causing the sheet to meander, and when the foam sheet is taken up and wound, the side surface becomes uneven. .

Therefore, an object of the present invention is to provide a preheating zone provided with a transport device for transporting a foamable polyolefin resin composition sheet, a release air nozzle for releasing the preheated sheet from the transport device, and a hot air discharge porous hole. In a method and a manufacturing apparatus for producing a crosslinked foam by a heating foaming zone provided with an air float bed having a membrane, (1) there is no variation in the width direction of the foam, and a constant width can be secured continuously, (2) ) When there is no meandering, the winding shape is uniform, and when the obtained foam is used for processing such as pasting with other materials, there is no need for operations such as meandering correction, and processing can be performed efficiently. Is to provide a manufacturing method and a manufacturing apparatus of a polyolefin resin crosslinked foam capable of being processed in-line after foaming.

As a result of further research by the present inventors, it was found that immediately before or after the end of free expansion foaming in the heating foaming zone,
It was found that the above object can be achieved by placing a guider equipped with a suction mechanism and introducing the guider into the take-up roll before the introduction.

The present invention has been completed based on these findings.

(Means for Solving the Problems) According to the present invention, a resin composition containing a polyolefin-based resin and a pyrolytic foaming agent is molded into a foamable resin composition sheet at a temperature lower than the decomposition temperature of the foaming agent. In the method for producing a continuous crosslinked foam in which foaming is performed and then crosslinked, the sheet is introduced into a foaming furnace having at least a preheating zone and a heating and foaming zone, and the preheating zone is transferred by a conveying device to preheat the sheet. After that, the preheated sheet is released from the conveying device by blowing air from the detaching air nozzle, guided to the air float bed having the porous membrane for discharging hot air, and blown with hot air to perform free foaming without contact and foaming. Provided is a method for producing a polyolefin resin crosslinked foam, which comprises passing a guider equipped with a suction mechanism near the end point. To be done.

Further, according to the present invention, a foaming furnace having at least a preheating zone and a heating foaming zone, the preheating zone is provided with a conveying device for transferring the expandable polyolefin resin composition sheet, At the terminal end, a separation air nozzle for separating the preheated sheet by blowing air from the conveying device is arranged, and in the heating and foaming zone, an air float bed having a porous membrane for hot air discharge is arranged, further, Provided is a device for manufacturing a polyolefin resin crosslinked foam, characterized in that a guider having a suction mechanism is arranged adjacent to the heating foaming zone.

Hereinafter, the present invention will be described in detail.

Specific examples of the method and apparatus of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view of a heating furnace according to the apparatus of the present invention. In FIG. 1, 1 is a preheating zone, 2 is a separation zone, 3 is a heating and foaming zone, 4 is a transport support belt, 5 is an air float bed having a porous membrane for discharging hot air, 6 is a heating device, and 7 is a separation. Air nozzle, 8,8 'is a resin composition sheet, 8 is a foamable resin composition sheet before foaming, 8'
Is a crosslinked foam, 9 is a guider equipped with a suction mechanism, 11, 1
1'is a take-up roll.

The foamable resin composition sheet 8 is carried on the carrying and supporting belt 4 and carried, and introduced into the preheating zone. In the preheating zone, the heating device 6 heats the preheating zone to a temperature just before the start of foaming at the end stage of the preheating zone.

Next, the foamable resin composition sheet is sent to the separation zone in which the separation nozzle 7 is arranged, and the foamable resin composition sheet is blown up by the ejection of air from the separation nozzle to be continuously separated from the transport support belt. To do. After that, it is guided to the air float bed 5 having a porous membrane for hot air discharge, where it is blown up by the hot air discharged through the porous membrane and heated to achieve free foaming without contact with solids. Then, the crosslinked foamed sheet 8'is formed.

The carrier usually comprises an endless carrier support belt. Examples of the support belt include a net made of metal and a net made of a heat-resistant resin such as polytetrafluoroethylene or a silicone resin. Considering the releasability, the net made of polytetrafluoroethylene is suitable.

The heating devices 6 in the preheating zone 1 and the heating and foaming zone 3 are
The apparatus is not particularly limited as long as it can raise the temperature of each zone to a desired temperature, but generally, an apparatus capable of performing radiant heating such as infrared rays and far infrared rays, heating with hot air, and the like is favored.

The separation of the expandable resin composition sheet from the transport support belt is smoothly achieved by blowing air uniformly in the width direction by the separation air nozzle, and no scratches or irregularities are generated on the surface of the sheet. The jetting speed and the jetting amount of the blown air are appropriately adjusted depending on the weight (width and thickness) of the foamable resin composition sheet. Further, the temperature of the jetted air is preferably equal to or higher than the decomposition temperature of the foaming agent so as to promote foaming. For example, when Azone Carbonamide is used as the foaming agent, it is preferably 160 to 300 ° C. In order to facilitate the detachment from the conveyance support belt, the detachment air nozzle is disposed at the end of the preheating zone and on the back surface of the support belt as shown in FIG. It is preferable that the preheated expandable resin composition sheet is released by jetting.

An air float bed having a porous membrane for discharging hot air includes, for example, a porous membrane made of glass fiber cloth coated with polytetrafluoroethylene resin and capable of uniformly discharging hot air. When the air float bed is a tilt type, the inclination angle thereof is usually 5 to 75 degrees, preferably 15 to 45 degrees, and the air float bed is arranged so as to be tilted downward according to the sheet transport direction. The porous film of the air float bed is arranged so as to face the back surface of the sheet separated from the transport device. The amount and speed of the hot air discharged from the porous film are adjusted by the weight (width is thickness) of the sheet. The temperature of the hot air is preferably 20 ° C. or more higher than the decomposition start temperature of the foaming agent in order to promote foaming. When azodicarbonamide is used as the foaming agent, 180 to 300 ° C is suitable. If the temperature is less than 180 ° C, the entire foaming does not become a complete foaming, the degree of foaming decreases, and if it exceeds 300 ° C, the surface deterioration of the polyolefin-based resin composition sheet occurs, and the surface bubbles may be broken.
It causes what is called an array. Since the foamable resin composition sheet is heated and foamed in a state of being completely floated (floating) by hot air, it does not cause scratches on the foam, and
Since air is discharged obliquely from the detaching nozzle and the porous film, a force that pushes up the sheet in the moving direction is generated at the same time as the sheet is blown up, and the tension applied to the sheet at the time of foaming is greatly reduced. The difference in molding strain in the width direction and the lateral direction can be extremely reduced. Also, in the air medium,
Since foaming is performed with low tension by heating, there is no difference between the front and back of the foam appearance.

FIG. 2 is a schematic plan view showing a state in which the expandable resin composition sheet 8 is freely expanded and expanded in the width direction and the thickness direction in a non-contact manner on the inclined air float bed 5 having the porous film for hot air discharge. It is a figure. The foam sheet 8'in the foam growth stage is passed through a guider 9 (disposed at the left and right ends of the sheet) having a suction mechanism near the end of foaming. The guider 9 includes a suction mechanism 10 connected to a suction device such as a vacuum pump (not shown).

The manufacturing method of the present invention is characterized in that a smooth foam having no molding distortion is obtained by free-foaming on an air float without contact and with almost no restriction. Limiting the width during the foaming process in the zone impairs these characteristics.
Therefore, a device (guider) for controlling the width and meandering is arranged near the foaming end point.

As a specific example of the guider, as shown in a schematic sectional view in FIG. 3, the foam sheet has a U-shaped cross section at both left and right ends, and the foam can be passed while being guided, Moreover, a device having a suction mechanism 10 connected to a suction device such as a vacuum pump can be mentioned. The suction mechanism guides while sucking both side surfaces of the foam sheet. Further, by sucking, the sheet deformed by the blowing of hot air in the air float bed can be flattened.

In addition, a porous body or a chain belt 12 can be arranged in front of the suction mechanism 10 to prevent the crosslinked foam sheet from being sucked into the suction mechanism 10. Furthermore, when a chain belt is used, if it is driven along the moving direction of the crosslinked foam sheet at almost the same speed as that of the crosslinked foam sheet, even if the crosslinked foam sheet comes into contact with the chain belt, smooth movement is achieved. Can be moved to.

Normally, it is desirable that the distance between the left and right guiders 9 and 9 is set to about 1.002 to 1.05 times that of the foam body designed when the free foaming is performed. If this interval is set too large, the foam sheet will be stretched in the width direction, causing residual molding strain. If it is set too small, the action and effect of width stabilization is reduced.

Positioning is performed near the end point of foaming by the guider, and then the film is taken up by the take-up roll and wound, so that the meandering is corrected and the winding side surface is not uneven. Also, free-width foaming is not hindered.

Thus, it is possible to obtain a foam that is suitable for aging molding (vacuum, compressed air, press molding, etc.) and has a beautiful appearance and that is free from scratches, irregularities, and front / back differences without fluctuations in width or meandering.

The polyolefin resin used in the method of the present invention is not particularly limited, and examples thereof include polyethylene (low density,
Medium to high density, linear low density), ethylene and vinyl acetate,
Acrylic acid, acrylates, copolymers with propylene, etc., homo- or copolymerized polypropylene, chlorinated polyethylene and the like can be mentioned, and these are each alone,
Alternatively, two or more kinds are mixed and used.

As the thermal decomposition type foaming agent, there are various kinds such as azodicarbonamide, oxybenzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, etc., but azodicarbonamide is generally used. The amount of foaming agent added is
Although appropriately adjusted depending on the desired expansion ratio, it is generally 2 to 25 parts by weight with respect to 100 parts by weight of the resin.

Further, a flame retardant, a colorant, an antioxidant, a filler, a foaming aid, a lubricant and the like can be optionally added to the foamable resin composition.

Crosslinking is generally carried out by a method in which an electron beam is applied by radiation or an organic peroxide such as dicumyl peroxide, but a method in which a crosslinking reactive vinylmethoxysilane or the like is grafted or copolymerized with a resin is also applied. it can. Also,
Various crosslinking methods may be used in combination. When cross-linking by irradiating ionizing radiation such as electron beam or radiation,
Usually, an irradiation step is provided before introducing the foamable resin composition sheet into a heating furnace, and the resin is crosslinked to obtain the viscoelasticity required for foaming. When heat-crosslinking in the presence of an organic peroxide, usually, the foamable resin composition sheet is cross-linked while being transferred through a preheating zone of a heating furnace.

(Example) Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Example 1] Low-density polyethylene (density 0.921, melt index
2.0) 100 parts by weight of azodicarbonamide as a foaming agent
15 parts by weight, zinc stearate as foaming aid and lubricant
Add 1.5 parts by weight and 1.0 parts by weight of titanium oxide as a pigment, premix with a Henschel mixer, put the mixture into a 90φ uniaxial extruder (L / D25), and keep the resin temperature below 150 ° C so that the foaming agent does not decompose. The temperature was adjusted, the mixture was kneaded and extruded, and then discharged from a T die to form a foamable resin composition sheet having a thickness of 1.75 mm and a width of 410 mm.

This sheet was irradiated with a dose of 4.8 Mrad using an electron beam irradiator (750 kv) to crosslink.

The crosslinked foamable resin composition sheet was introduced into the foaming device (using an infrared heater for heating) shown in FIG. 1 and transferred while being transferred on a polytetrafluoroethylene mesh support belt.
Heated to 155 ° C. At the end of the preheating zone, the heating sheet is blown up with 180 ° C warm air from the detaching nozzle,
It was led on a tilted air float bed with a porous membrane for hot air discharge with an oblique angle of 30 degrees. As the hot-air discharging porous film, a glass fiber cloth porous film coated with a polytetrafluoroethylene resin was used.

Hot air at 230 ° C was blown up from this porous film to allow it to expand freely, and passed through a suction and chain belt drive type guider attached at a left and right spacing of 1275 mm, then taken up by a take-up roll, then wound up on a roll A crosslinked foam sheet having a foaming ratio of 4.6 mm and about 31 times was obtained.

The cross-linked foam sheet obtained was evaluated per roll (200 m), and as a result, the width was between 1275 and 1280 mm, the meandering step was within 1 cm, and there was no scratch, unevenness, front and back surface, etc. Met.

[Comparative Example 1] A crosslinked foamed sheet was prepared in the same manner as in Example 1 except that a guider was not used.

The obtained crosslinked foam sheet was evaluated per one roll (200 m), and as a result, the width was widely varied from 1265 to 1280 mm, and the meandering step was extremely large at 8.5 cm.

The appearance of the foam was a homogeneous foam without scratches and the like.

(Effect of the Invention) According to the production method and the production apparatus of the present invention, a smooth and beautiful polyolefin-based resin crosslinked foam having a good appearance without scratches and irregularities similar to the rigid foaming method and having no front and back surface. Can be stably obtained. Further, the tension applied to the foamable resin composition sheet during heat foaming can be extremely reduced to obtain an isotropic crosslinked foam having almost no molding strain.

Moreover, by passing the guider near the end of foaming, it is possible to obtain a foam having a constant width and very few occurrences of meandering and the like.

Therefore, it is possible to provide a crosslinked foam excellent in heat-molding type processing suitability for a molded heat insulating material, a vehicle interior material, and the like, which are main applications of the polyolefin-based crosslinked foam.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a heating furnace according to the apparatus of the present invention. FIG. 2 is a schematic plan view showing a state where the resin composition sheet is expanded and foamed freely on the tilted air float bed. FIG. 3 is a schematic sectional view showing a specific example of the guider. 1: preheating zone, 2: detachment zone, 3: heating foaming zone, 4: transport support belt, 5: inclined air float bed having a porous membrane for hot air discharge, 6: heating device, 7: detachment air nozzle,
8: foamable resin composition sheet before foaming, 8 ': crosslinked foam sheet, 9: guider, 10: suction mechanism, 11, 11': take-up roll, 12: porous body or chain belt.

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Claims (2)

[Claims] 1. A resin composition containing a polyolefin resin and a thermal decomposition type foaming agent is molded into a foamable resin composition sheet at a temperature lower than the decomposition temperature of the foaming agent, and then crosslinked, followed by heat foaming. In a continuous method for producing a crosslinked foamed product, the sheet is introduced into a foaming furnace having at least a preheating zone and a heating and foaming zone, and the preheating zone is transferred by a conveying device to preheat the sheet, and then air is blown up from a releasing air nozzle. The preheated sheet is released from the conveying device, guided to the air float bed having a porous membrane for hot air discharge, and blown with hot air to perform free foaming without contact, and a guider equipped with a suction mechanism near the end point of foaming. A method for producing a polyolefin resin crosslinked foam, which comprises passing through 2. A foaming furnace having at least a preheating zone and a heating and foaming zone, wherein the preheating zone is provided with a conveying device for transferring the expandable polyolefin resin composition sheet, and the preheating zone is provided with an end portion thereof. Is equipped with a separating air nozzle for blowing up air to separate the preheated sheet from the conveying device, an air float bed having a porous membrane for hot air discharge is arranged in the heating foaming zone, and further, a heating foaming zone. An apparatus for producing a crosslinked foamed polyolefin resin, characterized in that a guider having a suction mechanism is disposed adjacent to.