JPS6050577B2 - Thermoplastic resin foam manufacturing method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for producing a thermoplastic resin foam.

There are various methods for producing thermoplastic resin foam, but when the foam has an unchanging cross-sectional shape, such as a sheet, it is best to make it by extrusion molding. It's normal.

However, making foams by extrusion is not as simple as making non-foams by extrusion. This is because when a foam is made by extrusion molding, immediately after the resin comes out of the die, it is greatly deformed due to foaming, making it difficult to form it into a desired cross-sectional shape. Therefore, when making a thermoplastic resin foam, in addition to the die, a passage for adjusting the shape of the foam is used, and this passage is attached to the extrusion hole of the die, so that the foamed resin extruded from the die is passed through the passage. Foaming was performed and the shape of the foam was adjusted.

The purpose of the passage in this case is to prevent the resin extruded from the die from being unduly deformed during foaming. On the other hand, the resin has the possibility of freely flying out in all directions other than the extrusion direction. Therefore, the passage was often surrounded on all sides and had a cylindrical shape. In order to adjust the shape of the foam to a desired shape using the above-mentioned shape adjustment passage, the passage must be sufficiently filled with the resin extruded from the die before proceeding.

To this end, conventional measures have been taken to constrict the end of the passage to provide resistance to the resin at the end of the passage, or to slow down the take-up speed of the molded body after exiting the passage. However, although giving resistance to the resin at the end of the passage seems to work in theory, in reality, the big problem is how to determine the squeezing ratio, and even if this problem is solved, Fluctuations in extrusion speed, resin temperature, expansion ratio, etc. cause pulsations in the resin coming out of the passages, sometimes causing large cracks in the foam. Furthermore, it is difficult to slow down the take-up speed of the molded product because it is difficult to adjust the speed and the resin is likely to be deformed after leaving the passage. For these reasons, it is difficult to obtain a foam with a desired shape, and a more suitable method has been desired. This invention was created in response to the above-mentioned demand.

The inventor used a shape-adjusting passageway with a non-tapered structure, and set this as the first passageway, and separately established a second passageway.
The second passage is separated from the first passage and attached to the tip of the first passage, and the second passage is constituted by only a pair of opposing plates to open the sides and prevent the movement of resin between the opposing plates. Attempts were made to provide resistance and to pool resin into the first passage through the second passage. That is, the inventor immediately put the foamable resin extruded from the extruder nozzle into the first passage, foamed it there, preliminarily shaped it, exposed it to the atmosphere, and then put it into the second passage. to provide resistance to the flow of resin in the second passage. An attempt was made to fill the first passage with resin. As a result, it was confirmed that a good foam could be easily obtained. This invention was made based on such confirmation. This invention uses a thermoplastic resin containing a blowing agent. The melt is extruded from a nozzle attached to the tip of the extruder into a shape that is wider than its thickness, and the extruded resin is immediately put into the first passage, where the cross-sectional shape of the foam is regulated from all sides. The foam is expanded in the width direction as well as the thickness direction, and then the foam is exposed to the atmosphere, and then the foam is introduced into the second passage, and the foam is released in the width direction in the second passage, and the foam is expanded in the thickness direction. The present invention relates to a method for producing a thermoplastic resin foam, which is characterized by providing low resistance to the movement of the foam and adjusting the shape of the foam.

Another invention related to the above invention is the invention of an apparatus used in the method.

The invention of the device is that a first passage is attached to the tip of the mouthpiece of the extruder, a second passage is attached at the end of the first passage with a gap,
A slit-shaped extrusion hole is bored in the nozzle, and a first passage is formed around the extrusion hole, forming a flat cylindrical structure that surrounds it on all sides. The shape expands in the width direction, and the second passage is configured with a pair of opposing walls along a flat surface to open the sides of the passage, and the thickness of the passage decreases as it advances or becomes equal in length. An apparatus for producing a thermoplastic resin foam, characterized by:
It is. Next, an embodiment of the method and apparatus of the invention will be described with reference to the drawings.

In that case, FIG. 1 is a longitudinal sectional view when the method of the invention is being carried out, and FIG. 2 is a horizontal sectional view of the same. That is, FIG. 1 corresponds to a sectional view taken along line I-1 in FIG. 2, and FIG. 2 corresponds to a sectional view taken along line 1--2 in FIG. Further, FIG. 3 is a partially cutaway vertical cross-sectional view showing another embodiment of the method of the present invention, and FIG. 4 is a cross-sectional view taken along the line -■ in FIG. In Figures 1 and 2, 1 is an extruder, 2 is a screw of the extruder, 3 is a mouthpiece, 4 is a resin melt containing a foaming agent, 5 is an extrusion hole, and 6 is a nozzle. 1 passage, 7 is a gap, 8 is a second passage, 9 is an upper and lower inner wall surface of the first passage, 10 is a left and right inner wall surface of the first passage, and 11 is an upper and lower inner wall surface of the second passage.

In order to understand the method of this invention, it is thought that it is easier to understand if the apparatus is explained first, so the apparatus will be explained below.

In FIGS. 1 and 2, the base 3 is provided with a slit-shaped extrusion hole 5 at its tip. A first passage 6 is attached to the cap 3. The first passage 6 is in close contact with the mouthpiece 3, and the resin discharged from the extrusion hole 5 immediately enters the first passage 6. The first passage 6 is limited by an inner wall surface 9 on the top and bottom, and is limited on the left and right by an inner wall surface 10, and is of a four-sided enclosed type. Among them, the interval between the upper and lower inner wall surfaces 9 is gradually increased along the direction in which the resin travels. On the other hand, the distance between the left and right inner wall surfaces 10 is only slightly increased along the resin traveling direction. In other words, the first passage 6 has a structure in which it expands largely in the thickness direction along the direction in which the resin travels, but does not expand very much in the width direction. Second
The passage 8 is provided apart from the first passage 6, and a gap 7 is formed therebetween.

The second passage 8 is composed of only two upper and lower plates for regulating the flat surface. That is, although there is an inner wall surface 11 in the vertical direction, there is no inner wall surface in the left-right direction, and it is in an open state. The distance between the inner wall surfaces 11 is gradually narrowed or equal along the direction in which the resin travels. The distance between the inner wall surfaces 1 on the inlet side of the second passage 8 is larger than the distance between the inner wall surfaces 9 on the outlet side of the first passage 6. Further, the distance between the inner wall surfaces 11 on the exit side of the second passage 8 is close to the thickness of the foam to be obtained. In this invention method, extrusion molding is performed as follows using the above-mentioned apparatus.

The foamable resin extruded from the extrusion hole 5 of the mouthpiece 3 is guided into the first passage, where it is foamed. The first passage does not expand very much in the width direction, but it expands greatly in the thickness direction, so the resin traveling through it will naturally foam gradually, and the passage will change its shape to the resin. Don't give it a big bulge that can be compressed from the outside. Therefore, the resin progresses smoothly in the first passage while being foamed. but,
If this continues, the first passage will not be filled with resin.
There is a possibility that it will pass through here. In order to avoid this, the present invention provides a second passage after the first passage.
In this invention, a gap 7 is provided between the first passage and the second passage. The gap 7 serves as a resin reservoir between the first passage and the second passage. That is, the amounts of each resin passing through the first passage and the second passage should always be equal in theory.
Although the amounts of each resin are supposed to be approximately constant, in reality, the amounts of each resin tend to fluctuate over time. In this way, when there is an instantaneous fluctuation in the amount of resin on one side, the gap 7 always stores resin there, so it increases or decreases the stored resin to soften the fluctuation. do. In addition, the gap 7 serves here to volatilize excess gas generated from the foam. This prevents the formation of cavities and deterioration of the surface due to vaporized gas in subsequent steps. In the method of the invention, the flat surface depth of the foam is restricted within the second passage.

The distance between the flat surfaces on the inlet side of the second passage (thickness of the passage) is wider than that on the outlet side of the first passage. Moreover, the second passage has a structure in which the thickness is made equal in length or the thickness is decreased along the traveling direction of the resin. The second passageway thus provides resistance to the foam moving therein and serves to fill the first passageway with resin. In this case, it seems that the second passage will provide a large resistance to the advancement of the resin, but in reality,
It doesn't offer much resistance. This is because both sides of the second passage are in an open state, so if a situation where it is likely to cause a large amount of resistance occurs, the resin will protrude to both the left and right sides, thereby reducing the resistance. thus,
The second passage will always provide a moderately low resistance to the flow of the resin without providing excessive resistance. Therefore, in the second passage, the resin fills the first passage appropriately.
It works well enough to flow without pulsation. Further, the thickness of the second passage is regulated to the thickness of the foam to obtain the passage shape on the exit side.

The second passageway also cools the foam passing therethrough. Thus, the foam that has exited the second passage has a flat shape with a desired thickness. The foam that has passed through the second passage is then further cooled and taken up by a take-up roll to become a product.

In FIGS. 1 and 2, the case indicated by the number 12 is
It is cooled there and taken up by a take-up roll indicated by number 13 to become a product. Incidentally, a through hole 14 is provided in the wall constituting the first passage and the second passage, and a heating or cooling medium is circulated within the through hole 14 to heat or cool the inner wall. It is desirable that The purpose and effect of heating or cooling are:
The first passage and the second passage are different. For example, by changing the temperature of the first passage, the structure of the foam can be changed. In more detail, the through hole 1 of the first passage
By circulating a cooling medium through the passageway and lowering the wall temperature of the passage, a low-foaming skin can be formed on the surface of the foam.
On the other hand, if the wall temperature is raised, the skin can be removed and the surface can be foamed well. However, lowering the wall temperature too much is undesirable because it impairs the flow of the resin, and conversely, raising the wall temperature too much is undesirable because it causes the destruction of bubbles and shrinkage of the foam. Therefore, the wall temperature should be appropriately adjusted depending on the type of resin and the expansion ratio. Generally, the wall temperature is ±5 based on the resin temperature when it exits the tip of the nozzle.
Preferably, the temperature is maintained within the range of 0°C. On the other hand, the second passage serves to fix the shape of the foam here, so it is desirable to cool it as much as possible. The second passage circulates water, which is normally at room temperature, to cool it. The apparatus used in the method of this invention is not limited to that shown in FIGS. 1 and 2.

For example, it may be as shown in FIGS. 3 and 4. 3 and 4 show a method for extruding the resin 24 into the first passage 26 from a flat extrusion hole 25 provided in the base 23, passing through the gap 27, and guiding it to the second passage 28. . In this case, the opposing inner wall surfaces in the thickness direction within the first passage 26 gradually open in the half 29 on the base side, and then become parallel to each other in the half 30 on the gap side. However, when looking at the inner wall surfaces 29 and 30 as a whole, the inner wall surfaces are opened with a larger ratio of the hole width at the outlet end to the hole width at the inlet end. On the other hand, the opposing inner wall surfaces in the width direction in the first passage 26 are opened at a large angle on the base side half 31, and are parallel to each other on the gap side half 32, so that they appear to be wide open as a whole. However, when looking at the inner wall surfaces 31 and 32 as a whole, the inner wall surfaces are only opened at a small ratio of the hole width at the outlet end to the hole width at the inlet end. Therefore, in the first passage, the entire inner wall surfaces 29 and 30 are
Compared to the entirety of the inner wall surfaces 31 and 32, it is wide open. Therefore, the first passage shown in FIGS. 3 and 4 meets the requirements of the present invention. It goes without saying that the second passage meets the requirements of the present invention. Of the devices shown in FIGS. 3 and 4, the first passage 26 is
It may be constructed from two parts by dividing the line A-A into two.

In FIG. 3, the line A-A is a line passing through the boundary between the inner wall surface 29 and the inner wall surface 30, and in FIG. 4, it is a line passing through the boundary between the inner wall surface 31 and the inner wall surface 32. In this way, dividing one passage into several parts does not depart from the scope of the present invention. In the method of the present invention, foam is preformed in a first passageway, and in order to complete the preformation, resistance is provided to the movement of the foam in a second passageway, and the first passageway is filled with resin. I have to.

Therefore, the preforming in the first passage takes place satisfactorily. Also, since there is a gap between the first passage and the second passage,
By accumulating the resin in the gap, fluctuations in the amount of resin flowing from the first passage to the second passage are alleviated, making the operation easier and making it easier to obtain a uniform product. Furthermore, since the generated gas escapes through the gaps, it is possible to prevent the formation of "stains" within the product and the deterioration of the surface condition. Moreover, since the foam is cooled and fixed in the second passage by contacting only the flat surfaces, it is possible to easily obtain a desired product of constant thickness at all times. Further, according to this method, a uniform foamed product having uniform and round cells can be obtained. Further, according to the method of the present invention, pulsations in the resin flow, cracks, and hard skin on the surface do not occur as in the conventional method. In this respect, the method and apparatus of the present invention are superior. Next, matters relating to the method and apparatus of the present invention will be individually explained in more detail.

In the method of this invention, various conventionally used blowing agents can be used as the blowing agent.

That is, it is possible to use either a solid compound that decomposes to generate gas when heated, or a liquid or gaseous compound that is impregnated into a resin under pressure and vaporizes in the resin when heated. Examples of the former include sodium bicarbonate and azodicarbonamide, while examples of the latter include aliphatic hydrocarbons such as carbon dioxide, butane, and pentane, and halogens such as methyl chloride, trichloromonofluoromethane, and dichlorodifluoromethane. There are carbonated hydrocarbons. Various thermoplastic resins can be used in the method of this invention.

As the resin, any of homopolymers, copolymers, mixtures of polymers, graft polymers, etc. can be used. From the viewpoint of the properties of the resin, those composed of monomers such as ethylene, propylene, vinyl chloride, styrene, and methyl methacrylate are preferred. Among these, the most preferred are polyethylene, polypropyne, polyvinyl chloride, etc., which are graft-polymerized with styrene or methyl methacrylate. This is preferable in terms of foam molding characteristics and quality characteristics in that it has both the characteristics of polyolefin, polyvinyl chloride, etc. and polystyrene or polymethyl methacrylate. Furthermore, partially crosslinked resins that have thermoplasticity can also be used. The blowing agent may be added to the thermoplastic resin either before or after the thermoplastic resin is introduced into the extruder.

That is, a thermoplastic resin may be impregnated with a blowing agent in advance and then placed in an extruder, or a thermoplastic resin that does not contain a blowing agent may be placed in an extruder and softened by heating. A blowing agent may then be included in the extruder. In addition to the blowing agent, various auxiliary agents can also be mixed with the thermoplastic resin in the method of this invention. As an adjuvant,
These include bubble control agents, flame retardants, colorants, fillers, etc. The foam control agent is, for example, something like finely powdered talc. In this invention, a conventionally known die having a flat linear extrusion hole can be used as it is.

That is, any types of caps conventionally called T-die, fan die, etc. can be used. In this case, "flat" means something that is wide relative to its thickness, such as what is called a sheet, board, board, etc.
This does not particularly mean that the absolute value of the thickness is small. As already mentioned, the first passage is where the sheet-like extrudate extruded from the extrusion hole of the nozzle, when foaming, flies out in the wrong direction and is later deformed to the extent that it is difficult to straighten it. The purpose is to prevent

That is, the first passage only has a preforming purpose. Therefore, although the shape of the outlet of the first passage does not need to exactly match the cross-sectional shape of the product to be obtained, it is preferable that the shape match as much as possible. The length of the first passage is
It is desirable that the distance be within a range of several centimeters to 20 centimeters along the direction of travel. The shape and size of the mouthpiece side of the passage are as follows:
The shape and size roughly match the extrusion hole of the die. It is desirable that the passage expands by 10 to 5 times in the thickness direction and 1.2 to 3 times in the width direction. 1st
The gaps provided between the passage and the second passage are in numerical order of 5,077,177! along the direction in which the resin travels. The range shall be .

Among these, preferred is about 10 mm. If this gap does not exist, the surface of the foam will not be clean. vice versa,
This gap should be avoided if it is too large, as this will tend to solidify the resin before it enters the second passageway. The second passage provides resistance to the flow of resin in order to fill the first passage with resin, and is used to ultimately determine the shape of the foam.

Therefore, it is desirable that the thickness of the second passage be slightly larger on the inlet side than on the outlet side of the first passage, and that the desired cross-sectional shape be obtained on the outlet side. The length of the second passage along the resin flow is preferably long, and is usually preferably 300 to 1000 WL. When the inner wall surfaces of the first passage and the second passage are coated with fluororesin, the foam sheet can easily slide on these surfaces.

Next, the details of the method of the present invention will be further explained with reference to Examples. Hereinafter, parts simply mean parts by weight. Example 1 Polystyrene was used as the thermoplastic resin and butane was used as the blowing agent.

The die used had an extrusion hole with a thickness of 1W$L1 and a width of 100TrIm. The first passage has a passage shape that is equal to the shape of the extrusion hole on the inlet side, and has a thickness of 25Tr7t and a width of 120mm on the outlet side, and is gradually expanded in the meantime, and has a length along the resin traveling direction of 50Tr7t.
1 was used. The second passage is 10Wf1 from the first passage.
It was placed at a distance. The length of the second passage is 300Tf0T
It was constructed by opposing two plates of L width or 500 T$L, and between them a passage of 28 TWL was formed on the inlet side and 30 cylinders and the outlet side. Therefore, the second passage had a length of 300 WTL along its traveling direction.
In addition, the inner walls of both the first passage and the second passage were coated with fluororesin to make them slippery. Mix 0.05 part of finely powdered talc as a bubble regulator with 1 part of polystyrene, put this mixture into an extruder, and press butane into the extruder so that the butane accounts for 1% by volume in the above mixture. west,
Set the resin temperature to 10 rC at the tip of the extruder, and
It was extruded at a rate of 23 kg per hour.

Oil at 130° C. was circulated within the walls of the first passage to heat the inner wall surface of the first passage. Moreover, the outer periphery of the second passage was cooled with air. In this way, the thickness is 30wn1 width is 240
? , it was possible to easily obtain a foam. This foam uniformly produced round, uniform cells, had a smooth and beautiful surface, had a density of 0.037 yIcc, and had the desired shape. Example 2 A thermoplastic resin obtained by graft polymerizing styrene monomer to polyethylene was used as described below.

Polyethylene 5CB was dispersed in water, 1 (4) parts of styrene monomer, 11 parts of benzoyl peroxide, and 0.8 parts of dicumyl peroxide were added thereto, and a polymerization reaction and a crosslinking reaction were carried out under heating. In this way, a graft polymer containing 25% by weight of ethylene and 75% by weight of styrene was obtained. The extruder and die were the same as those used in Example 1, and butane was press-injected into the resin in the extruder to give a butane content of about 11%.

A resin temperature cooling device is interposed between the extruder and the die,
The resin temperature was set at 108°C and the extrusion hole of the die was heated for 1 hour.
It was extruded at a rate of k9. As for the first passage, the shape of the passage on the resin inlet side is substantially equal to the shape of the extrusion hole of the base, and the thickness of the passage on the resin outlet side is 33 mm. , the width was 160 TWL, the width was gradually expanded, and the length along the resin traveling direction was 200 TWL.

A second passage was provided in a gap of 10 TWL from the exit of the first passage. The width of the second passage is 500Tf0! Two flat plates each having a length of 500T0n were placed opposite each other, and the distance between the plates was 35Tf$L on the inlet side and 30Tr0n on the outlet side. The inner walls of both the first passage and the second passage were coated with fluororesin to make them slippery. Inside the passage wall of the first passage,
A heating medium circulation channel was provided within a range of 50 Twt from the inlet side, and oil at 80'C was circulated through this channel.

In addition, room temperature water was circulated within the passage wall of the second passage to cool the passage. In this way, the extruded resin was guided into and passed through the first passage and the second passage. As a result, a plate-shaped foam having a thickness of (to) 2 (6) and a width of 2 (6) was obtained. This foam has a density of 0.028yIcc, foams uniformly,
It has the hardness of polyethylene and the softness of polyethylene, and the bubbles are spherical and fine.
The surface was smooth and had a beautiful appearance. Example 3 A thermoplastic resin obtained by graft polymerizing polyethylene monomers was used as described below.

Part A of polyethylene was dispersed in water, and stin monomer (12CiffI), 1 part of benzoyl peroxide, and 0.5 part of dicumyl peroxide were added thereto, and a polymerization reaction and a crosslinking reaction were carried out under heating. A graft polymer containing 4% by weight of ethylene and 6% by weight of styrene was obtained. This graft polymer was supplied to an extruder, and a blowing agent was pressurized into the extruder.

As the blowing agent, a mixture of dichlorodifluoromethane and methyl chloride was used in a ratio of 1:0.7. The foaming agent was press-fitted in an amount of 1% by volume of the total foaming agent. A resin cooling device was installed at the tip of the extruder, and the resin temperature was set at 105°C, and the extrusion hole was extruded at a rate of 58 kg for 1 hour through the extrusion hole of the die.
It was set to 0rfUn. As for the first passage, the shape of the passage on the inlet side is substantially equal to the extrusion hole, the shape of the passage on the outlet side is 50 mm thick, 16 mm wide, and the length along the direction of resin travel is 200 m. Tt was used.

The enlarged pattern of the passage in the first passage is 10cm from the entrance side. The maximum thickness is 507! 10 from the remaining exit side
For the part marked -, the thickness was 50 mm, the width was 160 mm, and the passage remained unchanged. A second passage was installed 20 times apart from the exit side of the first passage. As the second passage, the width is 50 mm.
C) Nrm, two boards with a length of 50mm are placed vertically facing each other, and the distance between them is 55T on the entrance side! UTL, exit side 52T
m! Tt was used. Both the first passage and the second passage,
The inner wall surface was coated with fluororesin to make it slippery. Oil at 75°C is circulated and heated within the walls of the first passage.
Room temperature water was circulated within the walls of the passage for cooling.

In this way, the thickness is 55T! Rm, width 300? A foam was obtained. This foam has a density of 0.027y1cc,
It foamed uniformly, the bubbles were spherical and fine, and the surface was smooth and beautiful in appearance. This foam was softer than the foam obtained in Example 2 and had performance suitable as a cushioning material.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing one embodiment of the method of the present invention, and FIG. 2 is a sectional view taken along the line ■--■ in FIG.

Claims (1)

[Claims] 1. A melted thermoplastic resin containing a foaming agent is extruded from a die attached to the tip of an extruder in a shape having a width larger than its thickness, and the extruded resin is immediately introduced into a first passage. Get in,
The cross-sectional shape of the foam is regulated from all sides in the first passage, expanded in the width direction as well as the thickness direction, then the foam is exposed to the atmosphere, and then the foam is put into the second passage. A method for producing a thermoplastic resin foam, which comprises releasing the foam in the width direction and pressing it in the thickness direction to provide resistance to the movement of the foam and to adjust the shape of the foam. 2. A first passage is attached to the tip of the extruder mouthpiece, a second passage is attached at the end of the first passage with a gap, a slit-shaped extrusion hole is bored in the mouthpiece, and the first passage is connected to the extrusion hole. The second passage has a flat cylindrical structure that surrounds it on all sides, and the passage expands in the thickness and width directions as it goes forward, and the second passage is formed by a pair of opposing walls along the flat surface. The passageway is characterized in that the sides of the passageway are opened, and the thickness of the passageway decreases or becomes equal in length as it advances. Thermoplastic resin foam manufacturing equipment.