JP2020183470A - Method for foaming pet resin - Google Patents

Abstract

To provide a method for foaming a PET resin using a metal salt produced by a neutralization reaction of a benzoic acid and sodium hydrogencarbonate as a foaming nucleus agent, which prevent occurrence of water caused by a neutralization reaction in a foam extruder.SOLUTION: A mixed molten PET resin is obtained by charging a PET resin, a chain extruder MB and a dehydrated reaction product nucleus agent MB into a foam extruder, and melting the PET resin, the chain extruder MB and the reaction product nucleus agent MB. Nitrogen gas, carbon dioxide gas or mixed gas of the nitrogen gas and the carbon dioxide gas is press-fit into the mixed molten PET resin in a state where an intermediate part of the foam extruder is maintained to be equal to or higher than a critical temperature and a critical pressure of the carbon dioxide gas, then the mixed molten PET resin is extruded from a die, and the mixed molten PET resin is foamed by the nitrogen gas, the carbon dioxide gas or the mixed gas.SELECTED DRAWING: None

Description

The present invention relates to a method for foaming a PET resin foam used for a heat insulating cup, a bin-break prevention packaging material, etc., and more specifically, sodium hydrogencarbonate or carbonic acid as a foaming nucleating agent in a supercritical foaming method for nitrogen gas or carbon dioxide gas. The present invention relates to a method for foaming a PET resin in which a metal salt of an organic acid is produced by reacting sodium with an organic acid, and the metal salt is used as a foaming nucleating agent.

Foams such as foam films and foam sheets are used in many fields because they have excellent heat insulation and cushioning properties. Insulation cups, bottle breakage prevention packaging materials, fruit packaging materials, automobile ceiling and door interior materials. It is widely used for such purposes.

There are two methods for foaming such a foam, chemical foaming and physical foaming. Chemical foaming is performed by sodium hydrogen carbonate, an azo compound such as azodicarboxylic amide, or P-toluneshonyl azide. Azide compounds such as N, N'-dinitrosopentamethylene tetramine and the like, chemical foaming agents that generate decomposition gas by heating were used, and these chemical foaming agents were kneaded. The resin was formed into a sheet using an extruder, and then foamed by heating in a heating furnace (see, for example, Patent Document 1).

Physical foaming uses a physical foaming agent consisting of low-boiling organic substances such as butane, isobutane, and dichlorodifluoromethane, and the physical foaming agent is press-fitted under high temperature and high pressure in which a predetermined resin is melted and kneaded by an extruder. Then, after adjusting to the optimum foaming temperature, the foam was extruded and placed in a low pressure zone (atmospheric pressure) to foam (see, for example, Patent Document 2).

However, in chemical foaming, the residue of the chemical foaming agent always remains unfavorable, and in the case of azo compounds, azide compounds, nitroso compounds, etc., there is a risk of producing carcinogenic amine compounds, so it is safe.・ It was unfavorable in terms of hygiene. Further, in physical foaming, butane and isobutane have a risk of explosion, and chlorofluorocarbon gas such as dichlorodifluoromethane has a problem of depleting the ozone layer.

Therefore, a method using carbon dioxide gas or nitrogen gas, which has no risk of explosion and is excellent in safety and hygiene, has been proposed. According to this method, a molten thermoplastic resin and supercritical material are used in a continuous plasticizer. A thermoplastic resin foam is produced by forming a molten resin composition in a state of being compatible with carbon dioxide or nitrogen in a state and discharging the molten resin composition from a die connected to the tip of a continuous plasticizer. Further, in order to make the foaming uniform, an inorganic fine powder such as talc was used as the foaming nucleating agent (see, for example, Patent Document 3).

By the way, in such a foaming method of the thermoplastic resin foam, fine powder talc or the like is used in order to make the bubbles uniform, but since the diameter of the talc is large, a large amount of talc must be added. That is, the effervescent nucleating agent stimulates the dissolved CO ₂ and N ₂ when they become a gas, and considering that one bubbling nucleating agent creates one bubble, fine bubbles are generated. It is necessary to add a large number of foam nucleating agents to make a large amount. Therefore, if the diameter of the talc is large, the weight is naturally large, so that a large amount of talc must be added. Further, when the diameter of the talc is large, the foamed cells formed are also large, so that the foam is easily broken. In addition, when the number of talc is small, talc with a small amount of dissolved gas is used as a nucleus for foaming, and as the number of foam cells decreases, the size of the foam cell itself increases, so that the foam is easily broken. is there.

Therefore, the applicant has no problems in safety, hygiene, danger of explosion, destruction of the ozone layer, etc., and sodium hydrogen carbonate or carbonic acid so that fine bubble cells can be uniformly formed. A foaming method using a metal salt produced by reacting sodium and an organic acid as a foaming nucleating agent has been proposed (see Patent Document 4).

Japanese Unexamined Patent Publication No. 7-41589 Japanese Unexamined Patent Publication No. 2000-158537 Japanese Unexamined Patent Publication No. 10-76560 Japanese Unexamined Patent Publication No. 2016-160306

In the foaming method, sodium hydrogen carbonate or sodium carbonate is reacted with an organic acid to form a metal salt, but since this reaction is a neutralization reaction, water is always generated. Therefore, there is a problem that water is generated in the process of putting the PET resin into the extruder together with the PET resin and kneading and reacting the resin.

That is, the water content of the PET resin affects the intrinsic viscosity (IV value) of the PET resin, and is 0.1 dl / g inside and outside when the water content is 50 ppm or less, and 0.2 dl / g when the water content is 200 ppm. It decreased inside and outside the g.

Further, since the amount of sodium hydrogen carbonate or sodium carbonate added to the organic acid is small, it is difficult to uniformly knead the PET resin even if it is sprinkled with liquid paraffin and adhered.

The present invention solves the above problems so that there are no problems in safety, hygiene, explosion risk, ozone layer depletion, etc., and fine bubble cells can be uniformly formed. An object of the present invention is to provide a method for foaming a PET resin, which prevents water from being generated in a foam extruder and can uniformly add a reaction product nucleating agent in a small amount.

The present inventors have diligently studied to achieve the above-mentioned problems, put sodium hydrogen carbonate or sodium carbonate and an organic acid into a foam extruder, and a metal salt serving as a reaction product nucleating agent inside the foam extruder. A master batch of a metal salt dehydrated in advance (hereinafter referred to as "MB") is prepared, and this MB is put into a foam extruder to mix the metal salt into the PET resin. It can be used as a foam nucleating agent.

In the method for foaming the PET resin according to claim 1, the PET resin, the chain extender master batch, and the dehydrated reaction product nucleating agent MB are put into a foaming extruder, and the PET resin, the chain extender MB, and the reaction are carried out. The product nucleating agent MB is melted to obtain a mixed molten PET resin, and nitrogen gas, carbon dioxide gas, or nitrogen gas and carbon dioxide gas are maintained in the middle portion of the foaming extruder while maintaining the critical temperature and pressure of carbon dioxide gas or higher. It is characterized in that the mixed molten PET resin is press-fitted into the mixed molten PET resin, then the mixed molten PET resin is extruded from a die, and the mixed molten PET resin is foamed with the nitrogen gas, carbon dioxide gas or the mixed gas.

In the method for foaming the PET resin according to claim 2, the reaction product nucleating agent MB is a mixture of benzoic acid or citric acid, which is solid at room temperature, and sodium hydrogen carbonate or sodium carbonate, which is solid at room temperature, in an equivalent relationship. The mixed powder and PETG resin or PE resin were put into an extruder, and benzoic acid or citric acid was reacted with sodium hydrogen carbonate or sodium carbonate in the extruder to cause sodium benzoate or sodium citrate as a reaction product nucleating agent. It is configured as a feature that it is a product of.

The method for foaming the PET resin according to claim 3 uses an extruder having two vent holes as an extruder, and sucks and removes the PET resin from the vent holes under a high vacuum of -99.99 kPa or more in a state of being heated and melted. It is structured to be careful.

The method for foaming the PET resin according to claim 4 is characterized in that the reaction product nucleating agent MB is added so that the weight ratio of sodium benzoate or sodium citrate is 0.01 to 0.2% by weight. It is configured.

The method for foaming a PET resin according to claim 5 is characterized in that the intrinsic viscosity (IV value) of the mixed PET resin at the time of foaming is 0.75 dl / g or more.

In the method for foaming a PET resin according to claim 6, the chain extender MB is added to the PET resin, and methyl styrene- (meth) acrylate-glycidyl methacrylate or pyromellitic anhydride having 9 to 10 epoxy groups / molecule. Is characterized by being kneaded.

The method for foaming a PET resin according to claim 7 is characterized in that an ethylene-acrylic acid-glycidyl methacrylate copolymer is added as a compatibilizer between the PET resin and the PE resin.

In the method for foaming the PET resin according to claim 1, the PET resin, the chain extender MB, and the dehydrated reaction product nucleating agent MB are charged into a foam extruder, and the PET resin, the chain extender MB, and the reaction are carried out. The product nucleating agent MB is melted to obtain a mixed molten PET resin, and nitrogen gas, carbon dioxide gas, or nitrogen gas and carbon dioxide gas are maintained in the middle part of the foaming extruder while maintaining the critical temperature and pressure of carbon dioxide gas or higher. The mixed gas of the above is press-fitted into the mixed molten PET resin, and then the mixed molten PET resin is extruded from a die, and the mixed molten PET resin is foamed with the nitrogen gas, carbon dioxide gas or the mixed gas.

In the present invention, the dehydrated reaction product nucleating agent MB is added to foam the PET resin. Therefore, unlike the conventional method, water is not generated in the foam extruder and the MB is also dehydrated, so that the MB-containing water is not mixed. As a result, the intrinsic viscosity due to hydrolysis of the PET resin is not lowered. As a result, the amount of the chain extender MB input can be reduced.

A mixed molten PET resin of PET resin and reaction product nucleating agent MB is prepared by using nitrogen gas, carbon dioxide gas or nitrogen gas and carbon dioxide gas in the middle part of the foaming extruder while maintaining the temperature above the critical temperature and critical pressure of carbon dioxide gas. Since the mixed gas of the above gas is press-fitted, the pressure inside the cylinder is 10 to 20 MPa, the temperature is 270 to 310 ° C., and the critical conditions of the nitrogen gas (critical temperature: -147.2 ° C., critical pressure: 3.29 MPa) and The carbon dioxide gas reaches a critical condition (critical temperature: 30.9 ° C., critical pressure: 7.38 MPa) or higher and dissolves in the molten PET resin. Then, since it is extruded from the die under atmospheric pressure, the gas becomes below the critical pressure, breaks the supercritical state, and becomes a gas. At that time, the reaction product nucleating agent stimulates the formation of uniform foam bubbles.

Further, since the chain extender MB is added, the low molecular weight PET resin can be modified into the high molecular weight PET resin having a three-dimensional structure, so that the viscosity can be improved, and thermal decomposition and water addition can be performed in the foam extruder. Even if the intrinsic viscosity decreases due to decomposition, it can be dealt with.

In the method for foaming the PET resin according to claim 2, the reaction product nucleating agent MB is an equivalent mixture of benzoic acid or citric acid, which is solid at room temperature, and sodium hydrogen carbonate or sodium carbonate, which is solid at room temperature. The mixed powder and PETG resin or PE resin were put into an extruder, and benzoic acid or citric acid was reacted with sodium hydrogen carbonate or sodium carbonate in the extruder to cause sodium benzoate or sodium citrate as a reaction product nucleating agent. Is generated. Therefore, benzoic acid or citric acid liquefies and soaks into solid sodium hydrogen carbonate or solid sodium carbonate to cause a neutralization reaction, and sodium benzoate (mp: 300 ° C. or higher) or sodium citrate (mp: 300). ℃ or more) can be generated.

In the method for foaming PET resin according to claim 3, when producing the reaction product nucleating agent MB, an extruder having two vent holes is used as an extruder, and the PETG resin or PE resin is vented in a heated and melted state. It is sucked and degassed from the hole under a high vacuum of -99.99 kPa or more. Therefore, since water is removed from the vent hole by suction and deaeration, it is possible to prepare a reaction product nucleating agent MB that is dehydrated and does not contain water.

In the method for foaming the PET resin according to claim 4, the reaction product nucleating agent MB is added so that the weight of sodium benzoate or sodium citrate is 0.01 to 0.2% by weight. When the weight of sodium benzoate or sodium citrate is less than 0.01% by weight, the number of foaming bubbles is reduced and the cell density is reduced. On the other hand, if it exceeds 0.2% by weight, the number of bubbles becomes larger than necessary and the foaming ratio cannot be increased.

In the method for foaming the PET resin according to claim 5, since the intrinsic viscosity (IV value) of the mixed PET resin at the time of foaming is 0.75 dl / g or more, the melt tension is large and foam breakage or the like occurs in the foamed sheet. There is nothing to do.

In the method for foaming a PET resin according to claim 6, the chain extender MB is a PET resin containing 9 to 10 epoxy groups / molecule, methyl styrene- (meth) acrylate-glycidyl methacrylate or pyromerit anhydride. Since the acid is kneaded, the PET resin can be modified well and reliably.

In the method for foaming a PET resin according to claim 7, an ethylene-acrylic acid-glycidyl methacrylate copolymer is added as a compatibilizer between the PET resin and the PE resin. Therefore, even when a PE resin is used for the reaction product nucleating agent MB, the PET resin and the PE resin can be compatible and kneaded uniformly. As a result, the reaction product nucleating agent is also uniform. Can be dispersed in.

Schematic diagram of an extruder for producing reaction product nucleating agent MB Schematic diagram of the cylinder part of the extruder for producing the reaction product nucleating agent MB Schematic diagram of an effervescent extruder for producing an effervescent sheet Schematic diagram of the cylinder part of an effervescent extruder for producing an effervescent sheet Micrograph of a cross section of the foam sheet of Example 1 Photomicrograph of a cross section of the foam sheet of Example 2

In the method for foaming the PET resin of the present invention, the PET resin, the chain extender MB, and the dehydrated reaction product nucleating agent MB are put into a foaming extruder, and the PET resin, the chain extender MB, and the dehydrated reaction are carried out. The product nucleating agent MB is melted to obtain a mixed molten PET resin, and nitrogen gas, carbon dioxide gas, or nitrogen gas and carbon dioxide gas are maintained in the middle portion of the foaming extruder while maintaining the critical temperature and pressure of carbon dioxide gas or higher. The mixed gas with the above is press-fitted into the mixed molten PET resin, and then the mixed molten PET resin is extruded from a die, and the mixed molten PET resin is foamed with the nitrogen gas, carbon dioxide gas or the mixed gas.

The reaction-generating part nucleating agent MB extrudes a mixed powder and PETG resin or PE resin in which benzoic acid or citric acid, which is solid at room temperature, and sodium hydrogen carbonate or sodium carbonate, which is solid at room temperature, are mixed in an equivalent relationship. Benzoic acid or citric acid is reacted with sodium hydrogen carbonate or sodium carbonate in an extruder to produce sodium benzoate or sodium citrate as a reaction product nucleating agent.

Therefore, there are the following aspects of the reaction product nucleating agent MB.
1. 1. MB of sodium benzoate using PETG resin
2. MB of sodium benzoate using PE resin
3. 3. MB of sodium citrate using PE resin

In the production of the reaction product nucleating agent MB, the inside of the extruder is the PETG resin extrusion temperature (200 to 240 ° C.) or the PE resin extrusion temperature (150 to 200 ° C.), so that benzoic acid (mp: 122 ° C.) is used. .4 ° C, Bp: 249 ° C) or citric acid (mp: 153 ° C, decomposition temperature: 175 ° C) becomes liquid and becomes solid sodium hydrogen carbonate (decomposed at 270 ° C) or sodium carbonate (mp: 851 ° C). It infiltrates and causes a neutralization reaction to produce a reaction product, sodium benzoate (mp: 436 ° C.) or sodium citrate (mp: 300 ° C. or higher).

Sodium benzoate (mp: 436 ° C.) and sodium citrate (mp: 300 ° C. or higher), which are reaction product nucleating agents, maintain a solid state at the extrusion temperature (270 to 310 ° C.) of the PET resin of the effervescent extruder. Since it can be formed, it can exert its function as a nuclear agent.

As an extruder for producing the reaction product nucleating agent MB, an extruder having two vent holes is used, and the PETG resin or PE resin is sucked from the vent holes under a high vacuum of -99.99 kPa or more in a heated and melted state.・ It is preferable to degas. That is, water is generated by the neutralization reaction of benzoic acid or citric acid and sodium hydrogen carbonate or sodium carbonate, and this water is removed from the PETG resin or PE resin by being sucked from the vent hole. Therefore, a dehydrated reaction product nucleating agent MB can be obtained.

The amount of the reaction product nucleating agent (sodium benzoate or sodium citrate) added to the PET resin by kneading the reaction product nucleating agent MB into the PET resin is 0.01 to 0.2% by weight. preferable. If the addition amount is less than 0.01%, the number of foaming bubbles is small and the cell density is low. On the other hand, if it exceeds 0.2% by weight, the number of bubbles becomes larger than necessary and the foaming ratio cannot be increased.

Hereinafter, a specific neutralization reaction will be described.
[For benzoic acid and sodium bicarbonate]

1 mol of benzoic acid reacts with 1 mol of sodium hydrogen carbonate to generate 1 mol of sodium benzoate, 1 mol of water and 1 mol of carbon dioxide.

The equivalent relationship is 1 mol of benzoic acid = 1 mol of sodium hydrogen carbonate = 1 mol of water = 1 mol of carbon dioxide.
[For citric acid and sodium bicarbonate]

1 mole of citric acid reacts with 3 moles of sodium hydrogen carbonate to generate 1 mole of sodium citrate, 4 moles of water and 3 moles of carbon dioxide.

The equivalent relationship is 1 mol of citric acid = 3 mol of sodium hydrogen carbonate = 1 mol of sodium citrate = 4 mol of water = 3 mol of carbon dioxide.

Both sodium benzoate and sodium citrate have a melting point of 300 ° C. or higher, and are solid at an extrusion temperature of 280 ° C. to 300 ° C. of the PET resin and serve as an effective foam nucleating agent for the molten PET resin.

By the way, the neutralization reaction reacts at the molecular size to produce a metal salt of an organic acid having a molecular size. It is not clear how many molecules of the produced metal salt of the organic acid gather to form an aggregate or crystal to form a foaming nucleating agent.

However, when the applicant applies a mixed powder having an equivalent relationship of citric acid and sodium hydrogen carbonate in Japanese Patent Application Laid-Open No. 2016-160306 (supercritical foaming method) [0070] [0071], the amount of the mixed powder is changed. Since the foam cell density increases or decreases in proportion to, it was clarified that the number of molecules of sodium citrate aggregate or crystal that contributes to foaming is 1.1 × 10 ¹⁰ .

The PET resin is foamed using the reaction product nucleating agent MB as described above, but the reaction product nucleating agent MB charged into the foam extruder is melted and kneaded with the PET resin, so that the reaction product The nucleating agent will be uniformly dispersed. Then, the PET resin and the molten PET resin of the reaction product nucleating agent are mixed with nitrogen gas, carbon dioxide gas or nitrogen gas and carbon dioxide gas in a state where the temperature and pressure of the carbon dioxide gas are maintained above the critical temperature and the critical pressure in the intermediate portion of the foaming extruder. Since the mixed gas of the above gas is press-fitted, the pressure inside the cylinder is 10 to 20 MPa, the temperature is 270 to 310 ° C., and the critical conditions of the nitrogen gas (critical temperature: -147.2 ° C., critical pressure: 3.29 MPa) and The carbon dioxide gas reaches a critical condition (critical temperature: 30.9 ° C., critical pressure: 7.38 MPa) or higher and dissolves in the molten PET resin. Then, since it is extruded from the die under atmospheric pressure, the gas becomes below the critical pressure, breaks the supercritical state, and becomes a gas. At that time, the reaction product nucleating agent stimulates the formation of uniform foam bubbles.

The chain extender modifies the PET resin into a high molecular weight PET resin having a three-dimensional structure so that foam extrusion can be performed satisfactorily. That is, when the intrinsic viscosity (IV value) at the time of foaming is low, the melt tension is small and the foam breaks at the time of foaming. Therefore, in order to prevent foam rupture, it is necessary to increase the intrinsic viscosity, and it has been found that the intrinsic viscosity is preferably 0.75 dl / g or more.

That is, the PET resin does not have to be a special PET resin, and is a PET resin for bottles having an intrinsic viscosity of 0.8 dl / g or more, or a PET resin for fibers having an intrinsic viscosity of 0.55 to 0.65 dl / g. Alternatively, PET resin of recovered PET flakes may be used, but these resins have low intrinsic viscosity. Further, when the PET resin is extruded by an extruder, its intrinsic viscosity decreases due to its thermal decomposition and hydrolysis. When the water content of the PET resin is 50 ppm or less, it decreases inside and outside 0.1 dl / g, and when the water content is 200 ppm, it decreases inside and outside 0.2 dl / g. Therefore, in consideration of these, it is preferable to adjust the amount of the chain extender added so that the intrinsic viscosity at the time of foaming is 0.75 dl / g or more.

As the chain extender, methyl styrene-methyl (meth) acrylate-glycidyl methacrylate or pyromellitic anhydride having 9 to 10 epoxy groups / molecule is preferable because of its high reactivity. Epoxy group

Or pyromellitic anhydride

は開裂して、カルボキシル基（−ＣＯＯＨ）、アルデヒド基（−ＣＨＯ）、水酸基（−ＨＯ）等の官能基と結び付き、ＰＥＴ分子鎖を３次元の網目構造の高分子にするとともに熱分解や加水分解による解重合によって生じたエチレングリコール、エチレングリコールから発生するアセトアルデヒドをも高分子の一部として捕捉する。

Cleaves and binds to functional groups such as carboxyl group (-COOH), aldehyde group (-CHO), hydroxyl group (-HO), and PET molecular chain becomes a polymer with a three-dimensional network structure, and is thermally decomposed and hydrolyzed. Ethylene glycol generated by depolymerization by decomposition and acetaldehyde generated from ethylene glycol are also captured as a part of the polymer.

The amount added to the PET resin is adjusted depending on the resin used as described above, but both methyl styrene- (meth) acrylate-glycidyl methacrylate and pyromellitic anhydride are in the range of 0.2 to 2.0% by weight. Is preferable.

As a method of adding to the PET resin, it is preferable to add it as MB (containing 10 to 30% by weight) of PETG resin or the like. When added as MB, the active ingredient of MB is in a diluted form, so that the variation in measurement and the variation in mixing can be reduced, so that the mixture can be uniformly mixed.

The amount of the chain extender methyl styrene- (meth) acrylate-glycidyl methacrylate or pyromellitic anhydride is preferably 0.2 to 2.0% by weight. If the amount added is less than 0.2% by weight, it is insufficient to modify the PET resin into a high molecular weight PET resin having a three-dimensional structure. On the other hand, if it exceeds 2.0 weight, the melt viscosity increases too much and the screw of the extruder is blocked.

Since the amount of the chain extender added is small as described above, it is preferable to add the chain extender as MB. The chain extender MB is preferable because the MB made of PETG resin has an affinity for PET resin and can be uniformly kneaded.

It is preferable to add an ethylene-acrylic acid-glycidyl methacrylate copolymer as a compatibilizer between the PET resin and the PE resin to the PET resin. That is, when a PE resin is used as the reaction product nucleating agent MB, the compatibility with the PET resin is small, so that this can be eliminated so that the reaction product nucleating agent can be uniformly dispersed and kneaded. When PETG is used as the reaction product nucleating agent MB, of course, no compatibilizer is required.

The amount of the compatibilizer added is preferably 1.0 to 4.0% by weight. If the amount added is less than 1.0% by weight, the PET resin and the PE resin cannot be compatible with each other. On the other hand, if the weight exceeds 4.0, impurities are simply added, and the characteristics of the PET resin are lost.

[Preparation of reaction product nucleating agent MB]
The reaction product nucleating agent MB was prepared using the extruders shown in FIGS. 1 and 2.

In FIGS. 1 and 2, reference numeral 1 is an extruder that sucks and degass the charged PETG resin, benzoic acid, and sodium hydrogen carbonate from the vent hole under a high vacuum of -99.99 kPa or more in a heated and melted state. After that, it is extruded.

A schematic diagram of the cylinder portion of the extruder 1 is shown in FIG. In FIG. 2, reference numeral 11 denotes a cylinder, and a screw 12 is provided inside the cylinder 11, and a first vent hole 13 and a second vent hole 14 are formed from the base end side (resin injection side). Pressurized compression portions 15 and seal portions 16 are alternately arranged on the screw 12, and in the seal portion 16, the groove width of the screw is narrowed, and the space between them is filled with molten PETG resin to fill the pressure and compression portions 15. The pressure difference between the high back pressure of 9807 to 19613 kPa (100 to 200 kg / cm ² ) and the high vacuum of -99.99 kPa of the vent holes 13 and 14 is sealed, and the resin is pushed only by the rotation of the screw 12. The molten PETG resin is prevented from blowing up from the vent holes 13 and 14 so as to proceed.

The vent holes 13 and 14 are connected to the oil rotary vacuum pump 18 via a condenser (condenser) 17, and the condenser 17 maintains the degree of vacuum and improves the oil quality of the oil rotary vacuum pump 18. It is for maintenance.

In the extruder as described above, in order to melt and extrude the PETG resin, PETG resin, benzoic acid and sodium hydrogen carbonate are charged into the cylinder 11, the extrusion temperature is inside and outside 280 ° C., and the back pressure is 9807 to 19613 kPa (100 to 200 kg /). cm ² ), from the vent holes 13 and 14, extrude while sucking and degassing under a high vacuum of -99.99 kPa or more. Therefore, in this extruded PETG resin, the water produced by the neutralization reaction of benzoic acid and sodium hydrogen carbonate is removed. Then, a reaction product nucleating agent MB is prepared from this PETG resin.

[Preparation of foam sheet; foaming of PET resin]
A foam sheet was produced by the foam extruder shown in FIGS. 3 and 4.

In FIGS. 3 and 4, reference numeral 2 denotes a foam extruder, in which the foam extruder 2 is provided with a screw 22 inside the cylinder 21, and the screw 22 is applied from the base end portion (left side in the drawing). The pressure compression section 23, the kneader section 24, and the pressure compression section 23 are formed. The pressure compression section 23 is formed with a normal groove width, and the kneader section 24 is formed with a narrow groove width. .. Therefore, in the kneader portion 24, the space between the grooves is filled with the molten PET resin, and the back pressure of the pressure compression portion 23 can be increased to 10 to 20 MPa.

An input port 25 for PET resin or the like is provided at the base end portion of the cylinder 21. A quantitative feeder 3 is arranged above the inlet 25. The metering feeder 3 is composed of a mixer 31 and a rotary valve 32, and a pressure inlet 26 for nitrogen or carbon dioxide gas is provided in the vicinity of the kneader portion 24 in the resin transport direction (right direction in the drawing). A flow meter 41, a plunger pump 42, and a gas cylinder 43 are sequentially connected to the pressure inlet 26. Further, a discharge port 27 for delivering the molten PET resin is provided at the tip portion, and a foam sheet winding means 28 is provided adjacent to the discharge port 27.

In the foam extruder 2 as described above, the PET resin, the chain extender MB, and the reaction product nucleating agent MB are charged through the quantitative feeder 3 and melt-kneaded. Further, nitrogen gas or carbon dioxide gas whose pressure is made constant by the plunger pump 42 is press-fitted from the gas cylinder 43 via the flow meter 41. Since the inside of the cylinder 21 of the press-fitted nitrogen gas or carbon dioxide gas has a critical temperature (31.1 ° C.) and a critical pressure (7.39 MPa) or higher of the carbon dioxide gas, both the nitrogen gas and the carbon dioxide gas are in a supercritical state. It dissolves in PET resin. Therefore, minute reaction products are uniformly kneaded in the PET resin, and nitrogen gas or carbon dioxide gas is dissolved in the PET resin. When extruded from the discharge port 27 in this state, the reaction product is released under atmospheric pressure. As a result, bubbles of nitrogen gas or carbon dioxide gas are generated using the reaction product as a foaming nucleating agent, and a foamed sheet is formed. Hereinafter, a more detailed description will be given.

In the cylinder 21, the area from the inlet 25 to the kneader portion 24 is the first stage, in which the reaction product nucleating agent and the chain extender are kneaded into the PET resin and uniformly dispersed and kneaded in the PET resin. The second stage is from the end face of the kneader portion 24 in the resin transport direction (right direction in the figure) to the discharge port 27, and nitrogen gas or carbon dioxide gas is press-fitted, and the nitrogen gas or carbon dioxide gas is injected into the PET resin. It is dissolved and kneaded in. When the nitrogen gas is press-fitted, it is set to the critical temperature (-147 ° C.) and the critical pressure (3.39 MPa) or higher of the nitrogen gas, but since both are lower than the critical temperature and the critical pressure of the carbon dioxide gas, the carbon dioxide gas The critical temperature and critical pressure of the above may be used as a reference.

Therefore, the temperature in the first stage is 260 ° C. or higher, which is the temperature at which the PET resin melts, and the pressure is more preferably 7.4 MPa or higher and 10 MPa or higher. In the second stage, the temperature and pressure need to be maintained in the state of the first stage, and are almost the same.

Hereinafter, a specific procedure for producing the foamed sheet will be described.

PET resin "CR8816" (intrinsic viscosity 0.81 dl / g, water content 400 ppm) manufactured by China Huajun Packaging Material Co., Ltd. was dried at 150 ° C. for 4 hours or more to reduce the water content to 50 ppm or less. 95.3 parts by weight of this PET resin, 3.5 parts by weight of pyromellitic anhydride MB (PETG 80% by weight + 20% by weight of Daicel Co., Ltd.), which is a chain extender, and a reaction product nucleating agent. 1.2 parts by weight of sodium benzoate MB (PETG 98.0% by weight + sodium benzoate 2.0% by weight) was uniformly mixed via a weight-based quantitative feeder 3.

The mixed PET resin obtained by mixing the anhydrous pyromellitic acid MB and the sodium benzoate MB is put into the foam extruder 2, and the mixed PET resin is melted at an extrusion temperature of 280 ° C., which corresponds to the second stage of the extruder. From the position, pressurized nitrogen gas pressurized to a constant pressure with a plunger pump was press-fitted and extruded from the T-die lip under atmospheric pressure to prepare a foamed sheet.

Since the critical temperature of nitrogen gas is -147.2 ° C and the critical pressure is 3.29 MPa, the temperature inside the cylinder of the extruder is 280 ° C and the pressure is 10 to 20 MPa, the nitrogen gas is in a supercritical state and mixed PET. It is dissolved in a resin, but when it is released under atmospheric pressure (0.1 MPa), the pressure is broken and the supercritical state is broken, and the dissolved nitrogen becomes a gas and foams. Various settings of the foam extruder 2 are shown below.

Cylinder size: 65 mmφ, L / D = 30
Pressure of 1st and 2nd stage: 17MPa
First stage temperature: 280 ° C
Second stage temperature: 280 ° C
Pressurized nitrogen gas injection amount: 32 ml / resin 100 g (atmospheric pressure equivalent)
T-die temperature: 270 ° C
T die lip gap: 0.8mm
Foam sheet take-up temperature: 6 m / min.

[Evaluation results]
The evaluation results of the obtained foamed sheet are shown in Table 1, and the electron micrograph (cross section) is shown in FIG.

The evaluation method for each item in Table 1 is as follows.
<Reaction product nucleating agent> Calculated from the concentration and amount of reaction product nucleating agent (sodium benzoate) MB added.
<Thickness;(μm)> Approximately estimated from the cross section of the electron micrograph.
<Specific gravity> A test piece is prepared by cutting a foam sheet into a square of 10 cm square, the thickness of the four sides of the test piece is measured with a micrometer, and the volume is calculated from the average value of the thickness and the surface area. The weight of the test piece was measured, and this weight was divided by the volume to calculate the specific gravity. Three test pieces were prepared and calculated from the average value.
<Effervescence Magnification> Calculated by dividing the density of PET resin (1.30) by the specific gravity.
<Foam cell density; (pieces / cm ³ )> The foam sheet is cut in the cross-sectional direction and the plane direction with a microtom, and the number of cells in each direction is measured from the enlarged photograph, and the cells per unit area (1 cm ² ) in the cross-sectional direction. It was calculated by multiplying the number by the number of cells per unit area (1 cm ² ) in the plane direction.
<Foam cell size; (μm)> The average plane direction and thickness direction were roughly measured from the cross section of the electron micrograph.
<IV value> A section was taken from the foamed sheet and measured according to ASTM D4603-03.

92.9 parts by weight of PET resin, 3.5 parts by weight of pyromellitic anhydride MB, and 3.6 parts by weight of sodium benzoate MB were uniformly mixed to make sodium benzoate MB three times as much as that of Example 1. A foamed sheet was prepared in exactly the same manner as in Example 1.

[Evaluation results]
The evaluation results of the obtained foamed sheet are shown in Table 1, and the electron micrograph (cross section) is shown in FIG.

From the above evaluation results, the following facts can be seen.
1. 1. In Example 2 in which the reaction product nucleating agent MB was added in an amount three times as much as in Example 1, the foaming cell density was also approximately three times, indicating that it was in direct proportion. Therefore, it can be seen that the amount of the foam product nucleating agent added should be adjusted in order to control the foam cell density.
2. It can be inferred that the injection amount of N ₂ gas should be controlled to control the foaming ratio. That is, if the amount of N ₂ gas be varied amount of the reaction product nucleating agent is the same, the expansion ratio is only almost the size of the unchanged cell is changed.
3. 3. The IV value is higher than the IV value (0.81) of the PET resin used. This is because the reaction product nucleating agent MB from which water was removed was used, so that water was not generated by the neutralization reaction in the foam extruder, and the IV value did not decrease due to the hydrolysis of the PET resin. It is considered to be the effect of the chain extender.

The reaction product nucleating agent MB was prepared in substantially the same manner as in Example 1 except that the PETG resin was used as a PE resin, the benzoic acid was used as citric acid, and the extrusion temperature was changed to 170 ° C.

Further, a foam sheet was produced using the foam extruder 2 in the same manner as in Example 1.

Hereinafter, a specific procedure for producing the foamed sheet will be described.

PET resin "CR8816" (intrinsic viscosity 0.81 dl / g, water content 400 ppm) manufactured by China Huajun Packaging Material Co., Ltd. was dried at 150 ° C. for 4 hours or more to reduce the water content to 50 ppm or less. 93.3 parts by weight of this PET resin and a chain extender, methyl styrene- (meth) acrylate-glycidyl methacrylate MB (PETG 80% by weight + BASF Japan Co., Ltd. ADR-4368-S 20% by weight) 3.5 By weight, 1.2 parts by weight of sodium citrate MB (PE98.0% by weight + sodium citrate 2.0% by weight), which is a reaction product nucleating agent, and ethylene, which is a copolymerizer between PE resin and PET resin. Two parts by weight of a-acrylic acid-glycidyl methacrylate copolymer (“LOTADER AX8840” manufactured by ARKEMA) was weighed using a weight-based quantitative feeder, and mixed uniformly with a mixer.

Using this mixed PET resin, a foamed sheet was produced in the same manner as in Example 1.

The evaluation results of the obtained foamed sheet are shown in Table 2.

1: Extruder 13, 14: Vent hole 18: Vacuum pump 2: Foam extruder 26: Press inlet 3: Metering feeder 42: Plunger pump 43: Gas cylinder

The method for foaming the PET resin according to claim 3 uses an extruder having two vent holes as an extruder, and the PETG resin or the PE resin is heated and melted from the vent holes under a high vacuum of −99.99 kPa or more. It is characterized by sucking and degassing.

In the present invention, the dehydrated reaction product nucleating agent MB is added to foam the PET resin. Since the PETG resin or PE resin is sucked and degassed under a high vacuum of -99.99 kPa or more in a heated and melted state , MB-containing water is not mixed. As a result, the intrinsic viscosity due to hydrolysis of the PET resin is not lowered. As a result, the amount of the chain extender MB input can be reduced.

The PET resin is foamed using the reaction product nucleating agent MB as described above. However, since the reaction product nucleating agent MB charged into the foam extruder is melted and kneaded with the PET resin, the reaction product is formed. The nucleating agent will be uniformly dispersed. Then, the PET resin and the molten PET resin of the reaction product nucleating agent are mixed with nitrogen gas, carbon dioxide gas or nitrogen gas and carbon dioxide gas in a state where the temperature and pressure of the carbon dioxide gas are maintained above the critical temperature and the critical pressure in the intermediate portion of the foaming extruder. Since the mixed gas of the above gas is press-fitted, the inside of the cylinder has a pressure of 10 to 20 MPa and a temperature of 270 to 310 ° C. , and the critical conditions of the nitrogen gas (critical temperature: -147.2 ° C., critical pressure: 3.29 MPa). And the critical conditions of carbon dioxide gas (critical temperature: 30.9 ° C., critical pressure: 7.38 MPa) or more, and the gas is dissolved in the molten PET resin. Then, since it is extruded from the die under atmospheric pressure, the gas becomes a gas below the critical pressure and the supercritical state is broken. At that time, the reaction product nucleating agent stimulates the formation of uniform foam bubbles.

In the extruder as described above, in order to melt and extrude the PETG resin, PETG resin, benzoic acid and sodium hydrogen carbonate are charged into the cylinder 11, the extrusion temperature is 220 ° C. and the back pressure is 9807 to 19613 kPa (100 to 200 kg / kg /). cm ² ), from the vent holes 13 and 14, extrude while sucking and degassing under a high vacuum of -99.99 kPa or more. Therefore, in this extruded PETG resin, the water produced by the neutralization reaction of benzoic acid and sodium hydrogen carbonate is removed. Then, a reaction product nucleating agent MB is prepared from this PETG resin.

Claims (7)

The PET resin, the chain extender MB, and the dehydrated reaction product nucleating agent MB are put into a foam extruder, and the PET resin, the chain extender MB, and the reaction product nucleating agent MB are melted and mixed and melted PET resin. At the same time, in the middle part of the foam extruder, nitrogen gas, carbon dioxide gas, or a mixed gas of nitrogen gas and carbon dioxide gas is press-fitted into the mixed molten PET resin while maintaining the critical temperature and pressure of carbon dioxide gas or higher. A method for foaming a mixed molten PET resin, which comprises extruding the mixed molten PET resin from a die and foaming the mixed molten PET resin with the nitrogen gas, carbon dioxide gas or the mixed gas. The reaction product nucleating agent MB extrudes a mixed powder and PETG resin or PE resin in which benzoic acid or citric acid, which is solid at room temperature, and sodium hydrogen carbonate or sodium carbonate, which is solid at room temperature, are mixed in an equivalent relationship. It is characterized in that benzoic acid or citric acid is reacted with sodium hydrogencarbonate or sodium carbonate in an extruder to produce sodium benzoate or sodium citrate as a reaction product nucleating agent. The method for foaming PET resin according to claim 1. The second aspect of claim 2, wherein an extruder having two vent holes is used as the extruder, and the PET resin is sucked and degassed from the vent holes under a high vacuum of −99.99 kPa or more in a state of being heated and melted. Method of foaming PET resin. The PET according to claim 1, 2 or 3, wherein the reaction product nucleating agent MB is added so that the weight ratio of sodium benzoate or sodium citrate is 0.01 to 0.2% by weight. Resin foaming method. The method for foaming a PET resin according to claim 1, 2, 3 or 4, wherein the intrinsic viscosity (IV value) of the mixed PET resin at the time of foaming is 0.75 dl / g or more. The chain extender MB is characterized in that a PET resin is kneaded with methyl styrene- (meth) acrylate-glycidyl methacrylate or pyromellitic anhydride having 9 to 10 epoxy groups / molecule. The method for foaming a PET resin according to claim 1, 2, 3, 4 or 5. The method for foaming a PET resin according to claim 1, 2, 3, 4, 5 or 6, wherein an ethylene-acrylic acid-glycidyl methacrylate copolymer is added as a compatibilizer between the PET resin and the PE resin.

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