JP3958751B2 - Dies for resin foam sheet molding equipment - Google Patents

Description

  The present invention relates to a die for a resin foam sheet molding apparatus capable of producing a foamed sheet of a thermoplastic resin excellent in appearance without causing a rough surface of the sheet and no adhesion of a resin decomposition product to the sheet surface. It is.

  As a method for producing a foamed sheet in a thermoplastic resin, an extrusion foaming method has been used conventionally. In brief, the thermoplastic resin is melt-kneaded in the extruder, the foaming agent is dissolved in this, and the molten resin is melted by the gap between the core of the molding die and the outer ring disposed downstream of the extruder. The foamed sheet is extruded from the formed resin flow path to the low pressure region and foamed. As a die applied to this, a T die or a round die is generally used depending on the target foaming ratio of the sheet or the sheet thickness.

As the foaming agent, a thermal decomposition type organic foaming agent such as an azo compound or a reactive organic foaming agent such as an isocyanate compound is often used as a chemical foaming agent. On the other hand, organic foaming agents such as aliphatic hydrocarbons such as butane and petane, and organic physical foaming agents represented by Freon are also frequently used.

However, various regulations have been enforced to protect the global environment and combat global warming. In chlorofluorocarbons, specific chlorofluorocarbons and alternative chlorofluorocarbons have been abolished. Yes. In addition, for butane and petane, the molding apparatus becomes large and it is necessary to use explosion-proof equipment.

  Under such circumstances, chemical foaming agents and inorganic physical foaming agents that use carbon dioxide and nitrogen gas are also starting to be used, especially for inorganic physical foaming agents, the amount of gas can be easily controlled. Since it is possible, application to a foamed product with a high foaming ratio and a foamed product with fine cells has attracted attention.

In particular, a round die is generally used for forming a sheet with a high expansion ratio. In order to achieve good foaming, a foaming agent is uniformly mixed in the molten resin in an extruder and a chemical reaction is performed on the pellet as a master batch. Many reactive organic foaming agents that generate carbon dioxide and nitrogen are also used.

Such cracked gas foaming is known to create a thermodynamically unstable state due to rapid pressure release near the die exit, and the foaming nuclei grow and foaming begins. The sheet is thickened in the thickness direction and guided to a mandrel disposed on the downstream side of the die while being in contact with the wall surface of the lip located at the downstream end of the die and cut at one or more locations around the mandrel. Molded.

  Therefore, since the sheet is pushed out while contacting the wall surface of the die lip, the surface of the foam sheet is rubbed against the wall surface, and the surface of the foam sheet is easily damaged depending on the planar accuracy of the wall surface and the slipping condition. In particular, this phenomenon appears remarkably in a round die that is frequently used in sheet molding with a high expansion ratio. The higher the expansion ratio, the more the resin is pushed out against the lip wall at the tip of the die, and the resin is pushed out.If the frictional resistance of this part is large, it becomes scratches and grows into a lump of resin called grains. Therefore, it adheres to the vicinity of the die lip and flows out to the inner and outer surfaces of the sheet or forms a streak line, thereby deteriorating the surface quality of the entire sheet.

In order to improve this phenomenon, in order to improve the surface accuracy of the wall surface of the round die and to reduce the sliding resistance to the wall surface during cooling and solidification in the molten resin, a sliding material is mixed in the molten resin and the contact surface is mixed. It is also used as a means to improve the smoothness of the.

As a method for improving the surface accuracy of the wall surface, the surface that contacts the melt of the outer ring of the round die is chrome-plated, and the surface that contacts the melt of the core is zirconia, alumina, titania, or two or more A technique for forming a mixture is disclosed (for example, see Patent Document 1).

  Also, the core body is coated with titanium nitride or tungsten carbide, and the outer ring body is coated with titanium nitride or tungsten carbide, or nitriding is performed to reduce the roughness of the sheet surface, and the resin decomposition product is used. A technique for preventing a certain spear from adhering has been disclosed (see, for example, Patent Document 2).

  Furthermore, a technique for anodizing the surface of an aluminum plug that is disposed downstream of the die and cools the foamed sheet is disclosed (for example, see Patent Document 3).

Also disclosed is a technique of coating the inner surface of the resin passage through which the resin of the die flows with a ceramic material (for example, see Patent Document 4).
JP-A-7-323458 JP 2000-246782 A JP 2000-254955 A JP-A-8-112857

However, the prior art is limited to a specific resin.
For example, a polyester resin is a crystalline resin that melts rapidly upon heating and becomes a low clay liquid. Therefore, it is necessary to increase the extrusion speed of the molten resin for molding. However, when the extrusion speed is increased, the frictional resistance between the wall surface and the molten resin flowing at a high speed becomes excessively large, and heat is generated, and a crack that is a decomposition product of the resin is generated to deteriorate the appearance of the sheet. Therefore, in order to reduce the frictional resistance, the surface of the round die that contacts the melt of the chrome is chrome plated, and the surface of the core that contacts the melt of zirconia, alumina, titania, or two or more However, since a high-viscosity resin has a large frictional resistance and generates heat, the high-viscosity resin cannot be foamed as intended.

  Also, in order to smoothly slide the foam sheet of polystyrene, polyester, polyethylene resin, the core body is coated with titanium nitride or tungsten carbide, and the outer ring body is coated with titanium nitride or tungsten carbide, or is nitrided. However, since the nitride coating is processed by vapor deposition, shrink fitting, etc., the surface is hard and processing time is required, which makes it difficult to apply.

  In addition, it is possible to eliminate black streaks and horizontal stripes on the foam sheet by making the plug aluminum and anodizing the surface, but it is possible to improve the surface accuracy and glossiness of the foam sheet and to reduce the eyes. Can't do it.

  Furthermore, by coating the inner surface of the resin passage of the die with a ceramic material, in the spiral resin passage, it has the effect of improving the fluidity of the resin in the spiral portion and preventing stagnation. It is not intended to improve the surface accuracy or reduce eye sag.

As described above, in the surface treatment of the mold specifying the material of the molded product in the conventional technique, the target is limited, and the narrow application range due to the difficulty of the surface treatment, particularly carbon dioxide gas etc. Correspondence to high expansion ratio due to is insufficient. Therefore, it is necessary to apply die surface accuracy that can cope with supercritical fluid foaming with a physical foaming agent with a high foaming ratio such as carbon dioxide or nitrogen instead of only with a foaming agent with a low foaming ratio. ing. Furthermore, there is a demand for surface accuracy that can handle not only low-viscosity resins to high-viscosity resins but also low-speed extrusion to high-speed extrusion.
Further, if the material of the coating surface of the mold is soft, wear may be accelerated, and if the coating layer is weakly bonded, peeling may occur.

  The present invention provides a mold die lip (core) to harden the coating layer and reduce the friction coefficient against the pressing wear on the die wall surface due to the foaming of the resin to increase the slipping property and prevent the occurrence of spears. And blasting on the surface of the outer ring), and more preferably, in this state, the upper surface is subjected to chromium nitride treatment, or chromium nitride treatment is applied to hard chrome plating to leave blast treatment traces on the surface, It is an object of the present invention to provide a die for a molding apparatus for a resin foam sheet having a surface coating that is well-fitted with a base of a plating layer, has improved surface lubricity, and has a low frictional resistance with a resin.

  The die for a resin foam sheet molding apparatus of the present invention is subjected to blasting treatment with appropriate roughness on both the core and the outer ring of the mold, and then nitrided over chromium nitride treatment or hard chrome plating treatment. By applying chrome treatment, smoothness is improved, and even if the pressure of the resin on the die wall surface is high, no creaking or streaking occurs at the lip, making it possible to form a foam sheet with good surface quality. it can. Furthermore, after blasting, the hard chrome plating and the chromium nitride treatment are more slippery than those with only the chromium nitride treatment, and the surface quality of the foam sheet can be further improved. it can.

  Further, since the frictional resistance of the molten resin to the die wall surface when discharged from the die is small and the extrusion pressure is reduced, the extrusion speed can be set fast.

  Moreover, since there is little frictional resistance, it can respond to a wide range of resin from high viscosity resin to low viscosity resin.

  Further, since the chromium nitride treatment is performed after the blast treatment, the chromium nitride treatment layer is surely coated, the wear resistance is reduced, and it can be used for a long time without peeling. Also, in the case of foaming with a supercritical fluid, especially when the foaming ratio is high, the foamed and thick resin layer is pressed against the core and the wall surface of the outer ring, especially the lip part. Can withstand use.

  Furthermore, even in the case of only the satin-like surface where only the blast treatment is applied, the surface accuracy of the foamed sheet is improved when a soft and low-viscosity resin is used.

  As described above, in the foam sheet molding, the surface accuracy and glossiness of the foam sheet are wide ranging from high foaming ratio to low foaming ratio, from low viscosity resin to high viscosity resin, and from low speed extrusion to high speed extrusion. It becomes possible to form a foamed sheet that does not cause streak-like patterns, as well as improvement, reduction in eyes.

  Blasting of the die lip (core and outer ring) of the mold is performed with a slightly rough finish, and more preferably, in this state, chromium nitride treatment is applied to the upper surface or chromium nitride treatment is superimposed on hard chrome plating. As a result, the blast treatment of the base remained on the surface, the plating layer was well blended with the base, the surface slipperiness was improved, and the surface coating with low frictional resistance with the resin was realized.

A first embodiment of the present invention will be described with reference to FIG.
This is an example and is not necessarily limited to this form.
The foam sheet forming apparatus of Example 1 includes an extruder (not shown) that melts and kneads a resin, and a resin passage 7 that is disposed on the downstream side of the extruder and that can discharge the resin mixed with the foaming agent to the outside. A round die 11 having a core 1 and an outer ring 2 that form a ring, a mandrel 9 that is disposed on the downstream side of the round die 11 and guides the foamed sheet 10 extruded from the round die 11, and a lower portion of the mandrel 9 And a cutter or an air knife (not shown) capable of cutting the foam sheet 10.

Next, the round die 11 will be described in detail.
The round die 11 includes a core 1 and an out ring 2, and a resin passage 7 is formed between the core 1 and the out ring 2. The resin passage 7 has a resin passage restricting portion 8 in which the width of the passage is narrowed so that the pressure of the resin rapidly increases due to the flow resistance of the molten resin when the molten resin flows in and passes through. The resin passage 7 has a passage from the end of the resin passage restricting portion 8 toward the end of the resin passage 7 so that the pressure is suddenly released after the pressure reaches the top at the end of the resin passage restricting portion 8. Lips 3 and 4 are formed in a tapered shape so that the width is gradually increased.

  The surface of the core 1 and the outer ring 2 on which the resin passages 7 are formed is blasted to form a blast layer 5, and the blasting is preferably roughened as a base treatment for plating, and the surface roughness (Ra) Is preferably in the range of 0.8a to 6.3a. If the surface roughness of the blast layer 5 is 0.8a or less, the plating is poor, and if it is 6.3a or more, the surface of the blast layer 5 is too rough and scratches may occur on the foam sheet 10. There is sex. Therefore, when the range passes through the lips 3 and 4 of the resin, traces of blasting remain, the contact area is low, an air layer is formed on the concave surface, the lubricity is improved, the contact resistance is lowered, and the surface quality is good. A foam sheet can be formed.

  After the blast treatment, the core 1 and the outer ring 2 are preferably subjected to chromium nitride treatment, more preferably chromium nitride treatment over the hard chrome plating treatment, and the surface treatment layer 6 is formed. The surface roughness (Ra) of the surface treatment layer 6 is preferably in the range of 0.4a to 3.2a. When the surface treatment layer 6 is 0.4a or less, the contact area of the sheet is increased and the extrusion resistance of the resin is increased. On the other hand, when the surface roughness is 3.2a or more, the surface uniformity of the sheet at the lips 3 and 4 may be lacking and streaky lines may be generated, which affects the surface accuracy.

Next, the manufacturing method of a foam sheet is demonstrated.
Foaming agents include pyrolytic organic foaming agents and reactive organic foaming agents, but in recent years, inorganic physical foaming agents such as carbon dioxide and nitrogen gas, which are less affected by global warming, are also used. In particular, when the purpose is to control foamed cells or to achieve a high foaming ratio, a physical foaming agent using carbon dioxide or nitrogen gas is preferred. More preferably, in the case of high foaming, it is preferable to dissolve carbon dioxide gas or nitrogen gas in the molten resin in the extruder in a supercritical state.

Hereinafter, this case will be described as an example.
The molten resin melt-kneaded in the extruder reaches the downstream round die 11 while the supercritical fluid is dissolved in the molten resin, is guided to the resin passage 7 and flows further downstream. At this time, when the molten resin passes through a narrow portion of the resin passage restricting portion 8, the resin pressure rapidly increases due to the flow resistance of the molten resin, and the pressure reaches the apex at the end of the resin passage restricting portion 8. Thereafter, when flowing through the lips 3 and 4 where the width of the resin passage 7 is widened toward the end of the round die 11, the molten resin is released from the pressure while being depressurized, and becomes a thermodynamically unstable state. Foaming of the supercritical fluid diffused into the molten resin begins, and the number of cells and cell density increase, and the cell diameter gradually grows and reaches the end faces of the lips 3 and 4.

  At this time, if the cooling of the foam sheet 10 and the outer surface in the vicinity of the end faces of the lips 3 and 4 is given by some means, the skin layer is quickly solidified, and the gas can be prevented from escaping to the outside. A foam sheet having a high or high expansion ratio can be obtained. On the other hand, if the gas escapes at this time, the sheet surface is rough and, in an extreme case, becomes a streak and remains on the sheet surface.

  At the tips of the lips 3 and 4, the foamed cells are pushed out while being grown and solidified and pressed against the tips of the inner and outer lips 3 and 4, and drawn along the outer periphery of the mandrel 9 on the extension line of the tapered portion. Taken downstream. At the lower part of the mandrel 9, the cylindrical foam sheet 10 is cut by an air knife or a cutter to form one or a plurality of foam sheets 10 and taken up by a winder (not shown).

  In this step, the contact pressure with respect to the surfaces of the lips 3 and 4 increases as the foaming ratio increases. Therefore, since the sheet surface quality varies depending on the surface roughness values of the lips 3 and 4, the range of the surface roughness becomes important.

  Further, when the passage resistance of the lips 3 and 4 is reduced, the temperature of the molten resin can be set to be low in accordance with the foaming conditions, so that the skin temperature of the molten resin is lowered and a thin skin layer can be formed. For this reason, gas escape from the sheet skin portion can be prevented, the number of foam cells is increased, the cell density is high, and a good foam sheet 10 that is not united with other cells is obtained.

  Considering these things, the resin passage resistance is small even at a low resin temperature in the lips 3 and 4, and the surface roughness of the core 1 and the outer ring 2 on which the resin passage 7 is formed and the lips 3 and 4 are suitable. It is important that the inner layer is in the inner side and the plating layer is not peeled off by the pressing force to the lips 3 and 4 at the time of foaming. From these facts, the surface treatment after the blast treatment and the surface roughness after the chromium nitride treatment have an important influence on the surface quality in sheet forming.

Next, FIG. 2 shows the result of an experiment using polystyrene for the difference in the quality of the surface of the foam sheet 10 due to the difference in the surface treatment between the core 1 and the outer ring 2.
Experimental example 1 is blasting only, Experimental example 2 is blasting and hard chrome plating, Experimental example 3 is blasting and chromium nitride treatment, Experimental example 4 is blasting, hard chrome plating and chromium nitride treatment Comparative Example 1 had no blasting or surface treatment, Comparative Example 2 had no blasting and only hard chrome plating, and Comparative Example 3 had no blasting and was subjected to hard chrome plating and chromium nitride treatment. Use things.

As a result, in Example 1, the surface of the foamed sheet 10 has a slight scratch on the basis of the eyes, but Examples 2 and 3 have no flaws such as streak, and in Example 4 There were no scratches such as streaks, and the surface of the foam sheet 10 was glossy.
On the other hand, Comparative Example 1 and Comparative Example 2 had scratches on the surface of the foamed sheet 10, and Comparative Example 3 had slight scratches starting from the eyes.

  As described above, by performing the blasting process, the surface roughness of the core 1 and the outer ring 2 is made to be in a suitable state, and further, by performing a surface process such as hard chrome plating or chromium nitride process, the above 0.4a-3 Good surface roughness in the range of .2a can be obtained. If the blast treatment is not performed, it can be said that a suitable surface roughness cannot be obtained even if the hard chrome plating or the chromium nitride treatment is performed as in Comparative Example 2 or Comparative Example 3.

  Therefore, the core 1 and the outer ring 2 are made of materials having a certain degree of thermal conductivity, and blasting is performed as a surface treatment. The effect of improving the surface accuracy of the sheet can be expected with only the blasted surface finish, but preferably, after the blasting treatment, chromium nitride treatment is applied, and more preferably, the chromium nitride treatment is overlaid on hard chrome plating. Install and keep the surface roughness within a suitable range. As a result, the blasting trace of the base remains, the frictional resistance is small, the slipperiness on the wall surface is increased, a stable flow of the molten resin is created, and a foam sheet with high surface accuracy is obtained.

  In addition, blasting is preferably performed using cinnabar sand, iron powder, glass beads, and the like, and if the trace is left on the chromium nitride construction surface to some extent, an air layer is formed between the resin contact surface and the lubricity is improved.

  Further, in order to improve the surface property, it is desirable that the flow rate of the resin at the lips 3 and 4 is not changed as much as possible, and the contact pressure to the lips 3 and 4 is almost the same and small. For this reason, in the lips 3 and 4, the angle and taper are appropriate and the flowability is good according to the extrusion pressure, extrusion speed and foaming ratio of the resin, and the shape capable of producing a stable flow is important along with the surface roughness. come.

  The supercritical fluid may be a subcritical fluid, or a simple gaseous material may be injected into an extruder, a chemical foaming agent may be used, or a reactive organic foaming agent may be used as a master batch. And may be mixed with the pellets and molded.

  Further, in the first embodiment, the round die 11 is used, but a considerable effect is produced even with the T die.

  In addition to foam molding, not only foaming but also ordinary sheet molding can be expected to improve sheet surface accuracy due to the lubricity of the resin passage surface.

2 is a cross-sectional view showing a round die of Example 1. FIG. It is a figure which shows the relationship between the surface precision of the contact surface with resin of a core and an out ring, and the surface quality of a foam sheet.

Explanation of symbols

  1 core, 2 out ring, 5 blast layer, 6 surface treatment layer, 7 resin passage, 10 foam sheet (sheet), 11 round die.

Claims (5)

A resin foam sheet molding apparatus for producing a foam sheet (10) in which a foaming agent is dissolved in a resin melt-kneaded in an extruder and extruded into a low pressure region through a mold disposed downstream of the extruder and foamed. Die for
The mold is a round die (11) having a resin passage (7) formed by a core (1) and an out ring (2), and the resin of the core (1) and the out ring (2). The surface on the side of the passage (7) is blasted ,
The surface roughness (Ra) of the blasted core (1) and the blast layer (5) of the outer ring (2) has a satin finish in the range of 0.8a to 6.3a,
Carbon dioxide gas or nitrogen gas inorganic gas is used as the foaming agent, the gas is dissolved in a molten resin in a supercritical state, and the pressure is released from the end of the resin passage restrictor (8) to the end of the resin passage. A die for a resin foam sheet molding apparatus, wherein the die is foamed. 2. The die for a resin foam sheet molding apparatus according to claim 1, wherein after the blast treatment, the blast layer (5) of the core (1) and the outer ring (2) is subjected to chromium nitride treatment . 3.   2. The resin foam according to claim 1, wherein after the blast treatment, the blast layer (5) of the core (1) and the outer ring (2) is subjected to a chromium nitride treatment process on a hard chrome plating. Die for sheet forming equipment.   The surface roughness (Ra) after the chromium nitride treatment of the blast layer (5) of the core (1) and the outer ring (2) is in the range of 0.4a to 3.2a. 2. A die for a resin foam sheet molding apparatus according to 2. The die for a resin foam sheet molding apparatus according to any one of claims 1 to 3, wherein any one of cinnabar sand, iron powder, and glass beads is used for the blast treatment.

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