WO2010106722A1 - Method for producing polyglycolic acid having lowered melt viscosity - Google Patents

Abstract

A method for producing a polyglycolic acid having a lowered melt viscosity which comprises: a hot water-immersion step of immersing a high-melt-viscosity polyglycolic acid in a solid form in hot water at 60-100^oC and allowing the polyglycolic acid to absorb moisture while maintaining the solid form thereof to give a moisture absorption polyglycolic acid having a water content greater than or equal to 1,000 ppm; and a heat drying step of drying the moisture absorption polyglycolic acid by heating while maintaining the solid form thereof to give a polyglycolic acid having a lowered melt viscosity.

Description

Process for producing low melt viscosity polyglycolic acid

The present invention relates to an efficient method for producing a low melt viscosity polyglycolic acid. According to the production method of the present invention, low melt viscosity polyglycolic acid can be obtained in a solid form such as pellets at room temperature. For this reason, low melt viscosity polyglycolic acid has good handleability and meterability, hardly generates gas components during melt molding, and has melt fluidity, melt stability, moldability, and adhesion to other materials. Etc.

Polyglycolic acid is a kind of biodegradable aliphatic polyester resin and is synthesized by ring-opening polymerization of glycolide or polycondensation of glycolic acid. According to the ring-opening polymerization of glycolide, a polyglycolic acid having a high molecular weight and a high melt viscosity can be obtained. Polyglycolic acid has a melting point of a homopolymer in the range of 215 to 225 ° C. and is excellent in heat resistance. In addition, polyglycolic acid is excellent in gas barrier properties.

Polyglycolic acid has a high melt viscosity, which may hinder new application development. As a new application, for example, polyglycolic acid is injection molded in the presence of another synthetic resin molded product placed in a mold, and the composite resin molded product and the polyglycolic acid layer are integrated. There are uses to manufacture products. If the polyglycolic acid has a high melt viscosity, it must be injection-molded at a high temperature and high pressure. Therefore, other synthetic resin molded products placed in the mold are produced by the flow of the molten polyglycolic acid during injection molding. Easy to deform.

There is a circuit board molded by injection molding as a special injection molded product. As a method for molding a circuit board by injection molding, a technique for forming a circuit pattern on the surface of a synthetic resin molded product by a two-time molding method (also referred to as “two-shot method”) has been developed. In the first shot of injection molding, a primary molded product is molded using a first synthetic resin (easy plating resin) containing a plating catalyst. The primary molding is moved to another mold or another cavity of the same mold. In the second shot, in the presence of the primary molded product placed in the mold, a second synthetic resin (hard-plating-resistant resin) that does not contain a plating catalyst is injected in a pattern to form a circuit other than the part that forms the circuit. The surface of the primary molded product is covered. A conductor circuit layer is formed by electroless plating on the surface of the primary molded product exposed without being covered with the second synthetic resin. Since the electroless plating layer is generally thin, it is grown to a thickness suitable for a conductor circuit by subsequent electroplating. After the plating step, the coating layer of the second synthetic resin can be left in an integrated state, but may be removed. Since the second synthetic resin is a hard-to-plate resin, the coating layer serves as a mask or resist for plating.

As another method, after the electroless plating is performed on the entire surface of the primary molded product made of the first synthetic resin obtained by the first shot injection molding, a thin plating layer is formed on the second shot, There is a method in which a synthetic resin is injected and integrated into a pattern, and a second synthetic resin coating layer is formed on the surface of the electroless plating layer other than the portion where the circuit is formed. The thickness of the electroless plating layer portion of the primary molded product exposed without being covered with the second synthetic resin is increased by electroplating. After the electroplating step, the coating layer of the second synthetic resin is removed together with the thin electroless plating layer below it. As a result, a circuit pattern-like plating layer remains on the surface of the primary molded product of the first synthetic resin.

A typical circuit board obtained by the two-time molding method is a three-dimensional injection molded circuit component called MID (Molded Interconnect Device) in which a conductor circuit is three-dimensionally formed on the surface of an injection molded product. MID is a three-dimensional wiring board that integrates injection moldings of synthetic resin and wiring components, contributing to rationalization of wiring, downsizing of electronic device parts, improvement of assembly, rationalization of equipment, space saving, etc. can do. MID is applied to semiconductor packages such as light emitting diodes, three-dimensional printed wiring boards, mobile phone antenna components, and the like.

Examples of the first synthetic resin used for the circuit board by injection molding include super engineering plastics such as liquid crystal polymer and polyphenylene sulfide; thermoplastic aromatic polyester resins such as polybutylene terephthalate and polyethylene terephthalate; polyamide resins; cyclic olefin resins Etc. are used.

Circuit boards such as MID obtained by the two-time molding method are difficult to make thinner, smaller, and lighter if the coating layer of difficult-to-plat resin is left on the product. It is necessary to use a resin material excellent in heat resistance, insulation, strength, chemical resistance, durability and the like. If a high-performance resin such as engineering plastic is used as a difficult-to-platable resin, it is necessary to perform injection molding at high temperature and high pressure. It is necessary to widen the width of the part. For this reason, it is desired that the hard-to-platable resin coating layer can be removed after the plating step.

The difficult-plating resin itself is required to have various performances. Since difficult-to-plat resin is used as a mask or resist for plating, it can form a coating layer with a precise pattern shape by injection molding, and has excellent adhesion to the surface of other synthetic resin molded products or electroless plating layers There is a demand for resistance to plating solutions used for electroless plating and electroplating, and easy peeling and removal after the plating step.

Japanese Laid-Open Patent Publication No. 2002-344116 (Patent Document 1) and Japanese Laid-Open Patent Publication No. 2004-247354 (Patent Document 2) propose using an aliphatic polyester resin such as polylactic acid as a hard-to-platable resin. . The aliphatic polyester resin has good adhesion to other materials, and the coating layer can be removed with an alkaline aqueous solution in a post-treatment process. However, since the aliphatic polyester resin has a relatively high melting point and a high melt viscosity, it must be injected at a high temperature and a high pressure during injection molding. For this reason, the aliphatic polyester resin easily deforms a primary molded product for forming a circuit board that is previously arranged in a mold during injection molding.

Under such technical standards, development of polyglycolic acid with excellent melt fluidity during injection molding is expected. If the melting point of polyglycolic acid is lowered, the melt fluidity at the molding temperature of ordinary polyglycolic acid can be improved. The melting point of polyglycolic acid can be lowered by a method of copolymerizing with other monomers. However, if the copolymerization ratio of other monomers is increased in order to significantly lower the melting point of polyglycolic acid, it becomes difficult to maintain the excellent characteristics of polyglycolic acid itself.

JP 2003-20344 (Patent Document 3) discloses a method of obtaining a low melt viscosity polyglycolic acid by adjusting the degree of polymerization during the synthesis of polyglycolic acid. Since low melt viscosity polyglycolic acid has high melt fluidity at the molding temperature of ordinary polyglycolic acid, injection molding at low pressure is possible.

However, the low melt viscosity polyglycolic acid obtained by adjusting the degree of polymerization at the time of synthesis has a high content of low molecular weight substances and is heated to the melt molding temperature as seen in the extremely low 3% thermal weight loss temperature. Then, the low molecular weight material contained therein is easily gasified and volatilized. When the low melt viscosity polyglycolic acid is likely to generate a gas component at a high temperature, when it is injection-molded on the surface of the primary molded product as a hard-plating resin, the generated gas component causes Adhesiveness of the polyglycolic acid coating layer is lowered, or the circuit board is contaminated.

Furthermore, low melt viscosity polyglycolic acid suitable for difficult-to-platable resins is difficult to pelletize. In order to produce pellets, it is necessary to melt the synthetic resin using an extruder and to extrude the melt into strands. The melt-extruded strand is pelletized by a method such as a cold cut that is cut after cooling, a hot cut that is cut at the die outlet, and an underwater cut that is cut in water. By pelletizing the synthetic resin, meterability, moldability, handleability, transportability, and the like can be improved.

Since the low melt viscosity polyglycolic acid has extremely high melt fluidity, it is difficult to form a strand having a uniform diameter even if it is melt-extruded in a strand form from an extruder. Polyglycolic acid with a particularly low melt viscosity is melted using an extruder and the strands droop even when continuously extruded from a die having holes into a strand shape. Impossible. Thus, pelletization is difficult for low melt viscosity polyglycolic acid. Low melt viscosity polyglycolic acid that has not been pelletized is inferior in meterability and moldability, so when injection molding is performed as a difficult-to-plate resin, it is difficult to form a coating layer having a precise pattern on the surface of the primary molded product. is there.

JP 2002-344116 A JP 2004-247354 A JP 2003-20344 A

The object of the present invention is excellent in melt fluidity, hardly generating a gas component at the time of melt molding, meterability, adhesion to other materials, precision moldability of fine patterns, plating resistance, solubility in alkaline aqueous solution, etc. Another object of the present invention is to provide a method for efficiently producing a low melt viscosity polyglycolic acid excellent in water.

A further object of the present invention is to provide a method for stably producing a low melt viscosity polyglycolic acid having the above-mentioned properties with good reproducibility. Another object of the present invention is to provide a new production method capable of arbitrarily controlling the melt viscosity of the low melt viscosity polyglycolic acid.

The inventors of the present invention have intensively studied on a method for obtaining a low melt viscosity polyglycolic acid that has excellent melt fluidity and hardly generates a gas component during melt molding. In the course of their research, they came up with a method that fundamentally changed the conventional idea of producing polyglycolic acid having a low melt viscosity during synthesis. The present inventors synthesized a high melt viscosity polyglycolic acid capable of being pelletized, formed a pellet from the resulting polyglycolic acid, and then absorbed the pellet, followed by heat drying treatment, It was found that polyglycolic acid having a significantly reduced melt viscosity can be obtained in the form of pellets, and a patent application was filed first (PCT / JP2008 / 0666162). According to this method, low melt viscosity polyglycolic acid having a solid shape such as pellets can be obtained.

When the polyglycolic acid is moisture-absorbed in a solid state such as pellets and then heat-dried, hydrolysis proceeds inside the solid-state polyglycolic acid and the melt viscosity is greatly reduced. The low melt viscosity polyglycolic acid obtained by this method has a low content of low molecular weight components to be gasified and gas at the melt processing temperature as seen in the decrease in the 3% thermogravimetric decrease temperature. Generation of ingredients is suppressed. Low melt viscosity polyglycolic acid is excellent in meterability and moldability because the shape of the pellet is maintained.

However, according to the above production method, the polyglycolic acid pellets are kept in a constant temperature and humidity chamber for a long time of 48 to 72 hours, or immersed in a warm water of 55 ° C. or less for a long time of 24 to 36 hours. Therefore, it was necessary to perform a moisture absorption treatment. Therefore, the production method has insufficient production efficiency.

Furthermore, in the manufacturing method, it has been found that even when the moisture absorption treatment step and the heat drying treatment step are performed under substantially the same conditions, there is a large variation in the melt viscosity of the low melt viscosity polyglycolic acid obtained in the same lot. did. For molding circuit boards such as MID by the two-time molding method, polyglycolic acid having a predetermined melt viscosity value is strongly required as a hard-to-platable resin. If the melt viscosity value of the low melt viscosity polyglycolic acid varies, it becomes difficult to coat it in a precise pattern by injection molding.

Therefore, as a result of researches to solve the above-mentioned problems, the present inventors implement a moisture absorption step of high melt viscosity polyglycolic acid in a predetermined solid form such as pellets or particles by immersion in hot water. At the same time, by increasing the temperature of the hot water within a specific range, the polyglycolic acid with sufficiently low melt viscosity was substantially retained in its original solid form even if the moisture absorption time was greatly reduced. It was found that it can be obtained as it is.

In addition, the present inventors improved the stirring conditions of the solid-form polyglycolic acid in warm water, resulting in homogeneous hydrolysis by subsequent heating and drying, and thereby the melt viscosity value in the same lot. It has been found that a low melt viscosity polyglycolic acid in which variation is remarkably suppressed can be obtained. Furthermore, prior to the heat drying treatment, the present inventors added moisture to the solid hygroscopic polyglycolic acid to adjust the total water content including the adhered water, thereby reducing the low melt viscosity polyglycolic acid. It has been found that the melt viscosity can be precisely controlled. The present invention has been completed based on these findings.

According to the present invention, the following steps 1 and 2
(1) A polyglycolic acid having a melt viscosity exceeding 100 Pa · s measured at a temperature 50 ° C higher than the melting point Tm of the polyglycolic acid (Tm + 50 ° C) and a shear rate of 122 sec ^-1 is 60-100 ° C in a predetermined solid form. Hot water immersion treatment step 1 for obtaining moisture-absorbing polyglycolic acid having a water content of 1,000 ppm or more by immersing in warm water and absorbing moisture while maintaining its solid form;
(2) The moisture-absorbing polyglycolic acid is heated and dried at a temperature in the range from 60 ° C. to 5 ° C. lower than the melting point of the polyglycolic acid (Tm−5 ° C.) while maintaining its solid form. The melt viscosity measured at a temperature 10 ° C. higher than the melting point of glycolic acid (Tm + 10 ° C.) and a shear rate of 1,200 sec ⁻¹ is 150 Pa · s or less, the 3% thermal weight loss temperature is 280 ° C. or more, and the water content is 500 ppm. Heat drying treatment step 2 for obtaining the following low melt viscosity polyglycolic acid;
A process for producing a low melt viscosity polyglycolic acid comprising

According to the production method of the present invention, it has excellent melt fluidity, hardly generates a gas component at the time of melt molding, meterability, adhesion to other materials, precision moldability of fine patterns, plating resistance, and against an alkaline aqueous solution. Low melt viscosity polyglycolic acid excellent in solubility and the like can be efficiently produced in a solid form such as pellets.

According to the present invention, it is possible to provide a method for stably producing a low melt viscosity polyglycolic acid having the above-mentioned properties with good reproducibility. Furthermore, according to the present invention, the melt viscosity of the resulting low melt viscosity polyglycolic acid can be more precisely controlled by adjusting the total water content of the hygroscopic polyglycolic acid prior to the heat drying treatment step. it can.

When the low melt viscosity polyglycolic acid obtained by the production method of the present invention is used as a hard-to-plate resin (mask resin) for a circuit board by a two-time molding method, it is possible to form and coat a fine pattern. Further, it is possible to prevent the circuit board from being contaminated due to the deformation of the primary molded product constituting the circuit board and the vaporization of the gas component during the injection molding. The coating layer of the low melt viscosity polyglycolic acid is excellent in resistance to the electrolytic plating solution and the electroless plating solution, is difficult to deposit metal plating particles, and can be removed with an alkaline aqueous solution after the plating step.

The polyglycolic acid is a homopolymer or copolymer containing a repeating unit represented by the formula — [— O—CH ₂ —CO —] —. The content of the repeating unit represented by the above formula in the polyglycolic acid is usually 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and the upper limit is 100% by weight. When the content ratio of the repeating unit represented by the above formula is too low, characteristics such as crystallinity, gas barrier properties, heat resistance, and chemical resistance inherent in polyglycolic acid are deteriorated.

Polyglycolic acid can be synthesized by dehydration polycondensation of glycolic acid, dealcohol polycondensation of glycolic acid alkyl ester, ring-opening polymerization of glycolide, and the like. Among these, according to the ring-opening polymerization method of glycolide, a polyglycolic acid (also referred to as “polyglycolide”) having a high molecular weight and a high melt viscosity can be easily produced. In the ring-opening polymerization method, glycolide is brought to a temperature in the range of about 120 ° C. to about 250 ° C. in the presence of a small amount of catalyst (eg, a cationic catalyst such as tin organic carboxylate, tin halide, antimony halide, etc.). The ring-opening polymerization is performed by heating. The ring-opening polymerization is preferably performed by bulk polymerization or solution polymerization.

To synthesize a polyglycolic acid copolymer, for example, ethylene oxalate, lactide, lactones (for example, β-propiolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, δ-valerolactone, β Cyclic monomers such as -methyl-δ-valerolactone, ε-caprolactone, trimethylene carbonate, and 1,3-dioxane; lactic acid, 3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic acid, 6 A hydroxycarboxylic acid such as hydroxycaproic acid or an alkyl ester thereof; substantially an aliphatic diol such as ethylene glycol or 1,4-butanediol and an aliphatic dicarboxylic acid such as succinic acid or adipic acid or an alkyl ester thereof. Equimolar mixtures; or these Using two or more may be copolymerized. Among these comonomers, the cyclic monomer is preferable. These cyclic monomers can be subjected to ring-opening copolymerization under the glycolide ring-opening polymerization conditions.

The comonomer is usually used in a proportion of 40% by weight or less, preferably 30% by weight or less, more preferably 20% by weight or less, based on the total amount of charged monomers. Among these comonomers, lactide, caprolactone, trimethylene carbonate, p-dioxanone, 5,5-dimethyl-1,3-dioxane-2-, are easy to copolymerize and easily obtain a copolymer having excellent physical properties. Preferred are cyclic monomers such as ON; and hydroxycarboxylic acids such as lactic acid.

Polyglycolic acid polymerization equipment includes: extruder type, vertical type with paddle blades, vertical type with helical ribbon blades, horizontal type of extruder type and kneader type, ampoule type, tubular type, flat plate type (square, It can be appropriately selected from various devices such as a rectangle.

The polymerization temperature can be set according to the purpose within a range from 120 ° C. to 300 ° C. which is a substantial polymerization start temperature. The polymerization temperature is preferably 130 to 250 ° C, more preferably 140 to 220 ° C, and particularly preferably 150 to 200 ° C. If the polymerization temperature is too high, the produced polyglycolic acid is susceptible to thermal decomposition. The polymerization time is usually in the range of 2 minutes to 50 hours, preferably 3 minutes to 30 hours, more preferably 5 minutes to 18 hours. If the polymerization time is too short, the polymerization does not proceed sufficiently, and if it is too long, the resulting polyglycolic acid is likely to be colored.

The melt viscosity of the polyglycolic acid used as a raw material in the present invention is usually more than 100 Pa · s, preferably 100 Pa when measured at a temperature 50 ° C. higher than the melting point Tm of polyglycolic acid (Tm + 50 ° C.) and a shear rate of 122 sec ^−1. · Exceeding s 3,000 Pa · s or less, more preferably 200 to 2,000 Pa · s or more, and particularly preferably 300 to 1,500 Pa · s. When the melting point of the polyglycolic acid homopolymer is 220 ° C., Tm + 50 ° C. becomes 270 ° C.

The weight average molecular weight (Mw) of the polyglycolic acid is usually in the range of 50,000 to 800,000, preferably 100,000 to 500,000, more preferably 150,000 to 300,000. The weight average molecular weight is a value obtained as a standard polymethylmethacrylate conversion value in gel permeation chromatography (GPC) measurement using hexafluoroisopropanol. If the melt viscosity or weight average molecular weight of polyglycolic acid is too low, pelletization becomes difficult. If the melt viscosity or the weight average molecular weight of polyglycolic acid is too high, it takes a long time to lower the melt viscosity, which is not efficient.

If desired, the raw material polyglycolic acid includes other thermoplastic resins, fillers, heat stabilizers, light stabilizers, waterproofing agents, water repellents, lubricants, mold release agents, coupling agents, pigments, dyes, etc. Various additives can be contained. These various additives are used in effective amounts according to their intended purpose.

A compound capable of exerting a heat stabilizing effect can be added to the raw material polyglycolic acid as a heat stabilizer. When the polyglycolic acid contains a heat stabilizer, the polyglycolic acid is hardly thermally decomposed, and the melt stability of the low melt viscosity polyglycolic acid is improved. Examples of heat stabilizers include heavy metal deactivators such as hydrazine compounds having —CO—NHNH—CO— units; phosphate esters having a pentaerythritol skeleton structure; at least one hydroxyl group and at least one long-chain alkyl ester group And at least one compound selected from the group consisting of a triazole compound, a hindered phenol compound, and a metal carbonate.

Examples of heavy metal deactivators include 2-hydroxy-N-1H-1,2,4-triazol-3-yl-benzamide and bis [2- (2-hydroxybenzoyl) hydrazine] dodecanedioic acid. It is done. Examples of the phosphate ester having a pentaerythritol skeleton structure include cyclic neopentanetetraylbis (2,6-di-tert-butyl-4-methylphenyl) phosphite and cyclic neopentanetetraylbis (2 , 4-di-tert-butylphenyl) phosphite. Examples of the phosphorus compound having at least one hydroxyl group and at least one long-chain alkyl ester group include mono- or di-stearyl acid phosphate. Examples of the metal carbonate include calcium carbonate and strontium carbonate.

The blending ratio of the heat stabilizer is usually 0.001 to 5 parts by weight, preferably 0.003 to 3 parts by weight, and more preferably 0.005 to 1 part by weight with respect to 100 parts by weight of polyglycolic acid. When the blending ratio of the heat stabilizer is too small, it is difficult to obtain a heat stabilizing effect, and when it is too large, the effect is saturated or various properties are deteriorated.

Polyglycolic acid with high melt viscosity has a temperature when the weight loss rate when heated reaches 3% (referred to as “3% thermal weight loss temperature”) around 350 ° C., and tends to generate gas components during melt processing Is relatively low. On the other hand, the low melt viscosity polyglycolic acid obtained by adjusting the degree of polymerization at the time of synthesis increases the content of the low molecular weight component, so that it depends on the degree of melt viscosity, but the 3% thermal weight loss temperature May drop to around 250 ° C. Thus, polyglycolic acid has a tendency to easily generate a gas component during melt processing when the melt viscosity becomes low.

The low melt viscosity polyglycolic acid obtained by the production method of the present invention has a characteristic that the 3% thermal weight loss temperature is maintained at a relatively high level. In order to further improve the thermal stability, it is preferable to add a thermal stabilizer to the high melt viscosity polyglycolic acid used as a raw material. Since the low melt viscosity polyglycolic acid obtained by adjusting the degree of polymerization at the time of synthesis is difficult to pelletize, it is difficult to pelletize by adding a heat stabilizer to the low melt viscosity polyglycolic acid. .

Since the high melt viscosity polyglycolic acid used as a raw material in the present invention has a high melt viscosity and melting point, it is in a solid state at room temperature (20 ± 15 ° C.) and maintains a solid state even at a relatively high temperature below the melting point. , In a predetermined solid form such as pellets or particles. In order to improve the meterability and moldability of the low melt viscosity polyglycolic acid as the target product, it is preferable to use pellet-shaped polyglycolic acid as the high melt viscosity polyglycolic acid of the raw material. When a high melt viscosity polyglycolic acid having a pellet shape is used as a raw material, the pellet shape is maintained in the warm water immersion treatment step and the heat drying treatment step, so that a low melt viscosity polyglycolic acid can be obtained in a pellet shape.

The pellets were prepared by supplying polyglycolic acid alone or polyglycolic acid and an additive component such as a heat stabilizer to the extruder, and changing the cylinder temperature to a temperature within the range of 260 ° C. from the melting point (Tm) of the polyglycolic acid. A method of melt-kneading, extruding into a strand from a die, cooling, and cutting can be employed. The size and the length of the pellet are usually in the range of 1 to 10 mm, preferably 1.5 to 8 mm, more preferably 2 to 6 mm, but are not limited thereto, and if necessary, A larger shape may be used.

The polyglycolic acid particles are preferably granules having an average particle diameter measured by a sieve separation method using a standard sieve, preferably 100 μm or more, more preferably 500 μm or more, and particularly preferably 1,000 μm or more.

The method for producing the low melt viscosity polyglycolic acid of the present invention includes the following steps 1 and 2.

(1) A polyglycolic acid having a melt viscosity exceeding 100 Pa · s measured at a temperature 50 ° C higher than the melting point Tm of the polyglycolic acid (Tm + 50 ° C) and a shear rate of 122 sec ^-1 is 60-100 ° C in a predetermined solid form. Hot water immersion treatment step 1 for obtaining moisture-absorbing polyglycolic acid having a water content of 1,000 ppm or more by immersing in warm water and absorbing moisture while maintaining its solid form;
(2) The moisture-absorbing polyglycolic acid is heated and dried at a temperature in the range from 60 ° C. to 5 ° C. lower than the melting point of the polyglycolic acid (Tm−5 ° C.) while maintaining its solid form. The melt viscosity measured at a temperature 10 ° C. higher than the melting point of glycolic acid (Tm + 10 ° C.) and a shear rate of 1,200 sec ⁻¹ is 150 Pa · s or less, the 3% thermal weight loss temperature is 280 ° C. or more, and the water content is 500 ppm. Heat drying treatment step 2 for obtaining the following low melt viscosity polyglycolic acid.

In the hot water immersion treatment step 1 of the present invention, polyglycolic acid (“high melt viscosity”) having a melt viscosity exceeding 100 Pa · s measured at a temperature 50 ° C. higher than the melting point Tm of polyglycolic acid (Tm + 50 ° C.) and a shear rate of 122 sec ^−1. Polyglycolic acid ”). The shape of the high melt viscosity polyglycolic acid may be a particle, but from the viewpoint of meterability, moldability, handleability, transportability, etc. of the resulting low melt viscosity polyglycolic acid, it is preferably a pellet. .

The mixing ratio of the high melt viscosity polyglycolic acid and water (warm water) is usually 1:10 to 10: 5, preferably 3:10 to 10: 7, more preferably 5:10 to 10: 8, by weight. Is within the range. When the amount ratio of water is too small, it becomes difficult to uniformly immerse the solid-form high melt viscosity polyglycolic acid in warm water and absorb moisture uniformly. When the amount ratio of water is too large, the thermal efficiency and the stirring efficiency are lowered.

In the present invention, it is preferable to perform the hot water immersion treatment step in a stirring tank. The stirring tank is not particularly limited as long as it has a shape such as an autoclave or a cylindrical tank and has heat resistance. The internal volume of the stirring tank is preferably 5 to 500 liters, more preferably 8 to 100 liters, and particularly preferably 10 to 50 liters from the viewpoint of processing efficiency and production scale. The stirrer is not particularly limited, however, for example, a stirrer including stirrer blades such as a flat plate paddle, an inclined paddle, a bull margin blade and its deformed blade, a full zone blade, and a wall wetter blade is preferable. The stirring blades may be one set or two or more sets may be arranged along the stirring shaft of the stirrer. According to technical common sense, the stirring blade has strength and length that can uniformly stir and mix the contents in the stirring tank according to the scale of the stirring tank.

The hot water may be preheated to a predetermined temperature, or may be warmed by heating in a stirring tank using low or normal temperature water at the time of preparation. Usually, water having a temperature equal to or lower than room temperature is charged into a stirring tank, heated to a temperature within a predetermined range by heating with a heating unit, and maintained at a predetermined temperature during the hot water immersion treatment process. As the heating means, a heating medium can be passed through a jacket provided on the bottom or side wall of the stirring tank, or a heater can be used.

The temperature of hot water is controlled within the range of 60-100 ° C. By controlling the temperature of the hot water within this predetermined range, the hot water immersion treatment (moisture absorption treatment) step can be carried out efficiently in a short time. From the viewpoint of enabling the hot water immersion treatment step to be efficiently performed in a short time and suppressing the content of low molecular weight substances contained in the finally obtained low melt viscosity polyglycolic acid, the temperature of the hot water is Is preferably controlled within the range of 60 to 95 ° C, more preferably 60 to 90 ° C, and particularly preferably 65 to 85 ° C. During the hot water immersion treatment, the temperature of the hot water can be varied within the above range, but in order to stably obtain a low melt viscosity polyglycolic acid having a predetermined melt viscosity with good reproducibility, During this time, it is desirable to maintain a predetermined temperature.

If the temperature of the hot water is too low, it takes a long time to absorb the polyglycolic acid by the hot water immersion treatment, and the production efficiency decreases. If the temperature of the hot water is too high, a partial hydrolysis reaction proceeds on the surface of the solid such as pellets in the hot water immersion treatment process, the degree of dispersion of the resulting hygroscopic polyglycolic acid becomes broad, and the proportion of low molecular weight components Increase. As a result, the low melt viscosity polyglycolic acid finally obtained has a high content of low molecular weight substances, and easily vaporizes gas components during melt processing. The increase in the content of the low molecular weight substance can be confirmed by a significant decrease in the 3% thermal weight loss temperature of the low melt viscosity polyglycolic acid.

In the warm water immersion treatment step, the degree of dispersion (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 2.15 by adjusting the temperature and treatment time of the warm water. Hereinafter, it is more preferable to obtain a hygroscopic polyglycolic acid of 2.10 or less in order to obtain a low melt viscosity polyglycolic acid having a low content of low molecular weight substances. The lower limit of the degree of dispersion is usually 1.30, and in many cases 1.50.

Polyglycolic acid has a specific gravity of about 1.60 g / cm ³ and is likely to settle in warm water. For this reason, even if a mixture of a solid form high melt viscosity polyglycolic acid and warm water is stirred in the warm water immersion treatment step, it is difficult to uniformly contact the fixed shape high melt viscosity polyglycolic acid with warm water. is there. On the other hand, by controlling the rotation speed of the stirring blade of the stirrer within the range of 100 to 500 rpm, preferably 150 to 300 rpm, more preferably 180 to 250 rpm, the high melt viscosity of the solid form in the hot water immersion treatment step It has been found that the polyglycolic acid can be uniformly contacted with warm water, thereby making it possible to absorb moisture uniformly. For this reason, in the subsequent heating and drying step, it is possible to obtain a low melt viscosity polyglycolic acid in which variation in melt viscosity value is sufficiently suppressed within the same lot.

When the mixture is not stirred in the warm water immersion treatment process or when the number of rotations of the stirring blade is small, the dispersion of the melt viscosity value in the same lot of the low melt viscosity polyglycolic acid tends to increase. Show. Even if the treatment time in the warm water immersion treatment process is increased, it is difficult to eliminate the variation in the melt viscosity value in the same lot. If the dispersion of melt viscosity values in the same lot is large, the quality control of the low melt viscosity polyglycolic acid becomes complicated and stable processing becomes difficult. It becomes impossible to sufficiently meet the demand in the technical field where polyglycolic acid is strongly demanded.

As the number of revolutions of the stirring blade decreases, the dispersion of the melt viscosity value in the same lot increases, and it becomes difficult to obtain a low melt viscosity polyglycolic acid having a desired melt viscosity value with good reproducibility. As the rotational speed of the stirring blade is increased, the variation in melt viscosity within the same lot tends to be reduced. However, even if the number of rotations of the stirring blade is increased too much, the effect of suppressing the dispersion of the melt viscosity value in the same lot is saturated, which is not efficient. In addition, if the number of rotations of the stirring blade is increased too much, a predetermined solid shape such as pellets may be damaged.

The treatment time in the warm water immersion treatment step is usually in the range of 1 to 15 hours, preferably 1.5 to 10 hours, and in many cases 2 to 8 hours. The treatment time can be appropriately selected according to the temperature of the hot water and the target moisture content. If the treatment time is too long, in addition to a decrease in production efficiency, undesired alteration and non-uniform hydrolysis may occur. Generally, the stirring time can be lengthened as the temperature of the hot water is lowered, and the stirring time can be shortened as the temperature of the hot water is raised.

If the temperature of the hot water in the hot water immersion treatment step is set to a low temperature of, for example, 55 ° C. or less, a long time of usually 30 hours or more is required to sufficiently absorb the solid form high melt viscosity polyglycolic acid. By setting the number of revolutions of the stirring blade within the range of 100 to 300 rpm and the temperature of the hot water within the range of 60 to 90 ° C, it is possible to efficiently prevent the melt viscosity variation within the same lot. Is particularly preferable.

In the warm water immersion treatment step, a hygroscopic polyglycolic acid having a water content of polyglycolic acid of 1,000 ppm or more, preferably 3,000 ppm or more, more preferably 5,000 ppm or more is obtained while maintaining the original solid form. . The upper limit of the moisture content is usually 50,000 ppm, preferably 30,000 ppm, more preferably 20,000 ppm. If the water content is too low, it is difficult to achieve a uniform and sufficient low melt viscosity in the heat drying process, and if it is too high, it is difficult to maintain a solid shape such as pellets or the content of low molecular weight components is low. It increases, and a long time is required for the heat drying process.

In the warm water immersion treatment step, the solid water polyglycolic acid such as pellets is subjected to warm water immersion treatment while substantially maintaining the original solid shape. After the warm water immersion treatment step, the water is usually removed by filtration or tilting with a filter. At this time, adhering water remains on the surface of the collected solid hygroscopic polyglycolic acid. Further, water remains in the gaps between the solid-state polyglycolic acids such as the deposited pellets. Since these residual waters are difficult to distinguish accurately, they are collectively referred to as adhering water. In the present invention, the moisture content means the amount of moisture contained in solid-state hygroscopic polyglycolic acid such as pellets. In the present invention, the amount of water, which is the sum of the amount of water contained in solid moisture-absorbing polyglycolic acid such as pellets and the amount of adhering water, is referred to as the total amount of water. The total water content is usually 15% by weight or less, often in the range of 2 to 10% by weight.

In the heat drying treatment step 2 of the present invention, the hygroscopic polyglycolic acid obtained in the step 1 is maintained at 60 ° C. to 5 ° C. lower than the melting point of the polyglycolic acid (Tm−5 ° C.) while maintaining the solid form. Until the melting point of the polyglycolic acid is 10 ° C. higher than the melting point (Tm + 10 ° C.), and the melt viscosity measured at a shear rate of 1,200 sec ⁻¹ is 150 Pa · s or less, 3% thermal weight reduction A low melt viscosity polyglycolic acid having a temperature of 280 ° C. or more and a water content of 500 ppm or less is recovered. The low melt viscosity polyglycolic acid naturally maintains a solid shape such as pellets at room temperature.

The heating and drying temperature is a temperature within a range from 60 ° C. to a temperature 5 ° C. lower than the melting point of polyglycolic acid (Tm−5 ° C.). The heat drying treatment temperature is preferably 70 to 200 ° C, more preferably 80 to 190 ° C, and further preferably 90 to 180 ° C. If the heat drying treatment temperature is too low, it takes a very long time to lower the melt viscosity of the hygroscopic polyglycolic acid to a desired level. On the other hand, if the heat drying treatment temperature is too high, it becomes difficult to maintain the solid state of the hygroscopic polyglycolic acid.

The heating and drying treatment time is performed until the melt viscosity of the hygroscopic polyglycolic acid is lowered to a desired level. The heat drying time is preferably 1 to 200 hours, more preferably 2 to 150 hours, and particularly preferably 3 to 100 hours. When a method of performing heat drying treatment while flowing hot air such as heated nitrogen or air is employed, the treatment time can be shortened to a range of preferably 3 to 15 hours, more preferably 4 to 10 hours. The time for the heat-drying treatment until the desired melt viscosity level is reached also varies depending on the heat-drying treatment temperature. In general, the higher the heat drying temperature, the higher the desired melt viscosity level can be reached in a relatively short time.

In the production method of the present invention, high-quality low melt viscosity polyglycolic acid can be obtained efficiently by adopting a method of drying simultaneously with heating. In order to perform the heat drying treatment, it is desirable to heat in a dry inert gas or air atmosphere. As the dry inert gas, for example, it is desirable to use dry nitrogen having a dew point of usually −60 ° C. to −10 ° C., preferably −50 ° C. to −30 ° C., and in many cases −40 ° C. The dry air is preferably air that has been dehumidified by removing dust through a filter. The heat drying treatment can be carried out by placing the solid-form hygroscopic polyglycolic acid in a high-temperature treatment machine under dry heat conditions such as an oven. It is desirable to carry out while flowing an inert gas or air. Dry nitrogen and dry air can also be supplied as hot air heated to a predetermined heat treatment temperature.

The flow rates of the inert gas and air depend on the amount of hygroscopic polyglycolic acid and the total amount of water, but are usually 0.1 to 30,000 liters / minute, preferably 1 to 10,000 liters / minute, more preferably Is in the range of 5 to 5,000 liters / minute, particularly preferably 10 to 1,000 liters / minute.

According to the production method of the present invention, a low melt viscosity polyglycolic acid having a melt viscosity of 150 Pa · s or less measured at a temperature 10 ° C. higher than the melting point of polyglycolic acid (Tm + 10 ° C.) and a shear rate of 1,200 sec ⁻¹ is obtained. Obtainable. Since low melt viscosity polyglycolic acid has a low melt viscosity, its melt viscosity is measured at a temperature 10 ° C. higher than the melting point of polyglycolic acid (Tm + 10 ° C.) and a shear rate of 1,200 sec ⁻¹ .

When the melting point of polyglycolic acid is 220 ° C, the measurement temperature is 230 ° C. The lower limit of the melt viscosity of the low melt viscosity polyglycolic acid is usually 1 Pa · s. However, in the present invention, as long as the polyglycolic acid maintains a solid shape such as pellets at room temperature (20 ± 15 ° C.), the temperature is 10 ° C. higher than the melting point of polyglycolic acid (Tm + 10 ° C.) and the shear rate is 1,200 sec. ^Even when the melt viscosity measured under the condition of ^-1 is so low that the melt viscosity cannot be measured, it is evaluated that the melt viscosity is 150 Pa · s or less.

When using low melt viscosity polyglycolic acid as a hard-to-platable resin (mask resin) for circuit boards by a two-time molding method, melt it to avoid deformation of the primary molded product during the second shot of injection molding. It is desirable to reduce the viscosity to 130 Pa · s or less, further 100 Pa · s or less, and in many cases 80 Pa · s or less. The low melt viscosity polyglycolic acid has a better melt fluidity at the time of injection molding as its melt viscosity is lower, and can reduce the pressure at the time of injection. When the primary molded product is molded using a synthetic resin that is not sufficiently high in heat resistance, it is preferable that the melt viscosity of the polyglycolic acid used as the mask resin is as low as possible. On the other hand, when the low melt viscosity polyglycolic acid cannot maintain a solid state such as pellets, handleability, meterability, moldability and the like are lowered.

The reason why the melt viscosity of polyglycolic acid is lowered by the production method of the present invention is presumed to be because the hydrolysis reaction proceeds in the solid-state polyglycolic acid that has absorbed moisture in the heat drying treatment step. By controlling the hot water immersion treatment conditions and the heat drying treatment conditions in the solid state as described above, a homogeneous and moderate hydrolysis reaction can be caused while maintaining the solid state like pellets, and low molecular weight components High-quality, low melt viscosity polyglycolic acid can be obtained in a solid state while suppressing the formation of.

The 3% thermogravimetric reduction temperature of the low melt viscosity polyglycolic acid obtained by the production method of the present invention is 280 ° C. or higher, preferably 290 ° C. or higher, more preferably 300 ° C. or higher, particularly preferably 320 ° C. or higher. . The upper limit of the 3% thermal weight loss temperature is usually 355 ° C. The 3% thermogravimetric temperature reduction temperature of the low melt viscosity polyglycolic acid of the present invention is preferably improved by containing a small amount of the specific heat stabilizer, but the use of a heat stabilizer is not always necessary.

In contrast, the low melt viscosity polyglycolic acid obtained by adjusting the degree of polymerization during synthesis has a high content of low molecular weight components, and its 3% thermal weight loss temperature is usually 260 ° C. or less, in many cases It becomes around 250 ° C. The low 3% thermal weight loss temperature of polyglycolic acid means that low molecular weight components are easily gasified during melt processing such as injection molding. The low melt viscosity polyglycolic acid obtained by adjusting the degree of polymerization at the time of synthesis has a large content of low molecular weight components, so even if it contains the specific heat stabilizer, its 3% thermal weight loss temperature is greatly increased. It is difficult to improve.

The low melt viscosity polyglycolic acid is a dry polymer having a water content of 500 ppm or less, preferably 300 ppm or less, more preferably 200 ppm or less, and particularly preferably 100 ppm or less. The lower limit of the moisture content is about 2 ppm. When the water content of the low melt viscosity polyglycolic acid is too high, the storage stability is lowered, and moisture is easily gasified during molding. A low melt viscosity polyglycolic acid having a low water content can be obtained by carrying out heat treatment under dry conditions.

According to the production method of the present invention, the melt viscosity of the low melt viscosity polyglycolic acid can be controlled by controlling the treatment conditions of the hot water immersion treatment process. In addition to this, in the heat drying treatment step 2 of the production method of the present invention, water is added to the hygroscopic polyglycolic acid, and the total water content including the amount of water contained in the solid such as the pellets and the amount of adhering water By controlling the amount and then drying by heating, the melt viscosity of the low melt viscosity polyglycolic acid can be precisely controlled.

Specifically, after the hot water immersion treatment step 1, water is removed by filtration with a filter or tilting. Since the wet hygroscopic polyglycolic acid is in a solid form such as pellets, it contains adhering water such as residual water adhering to the surface in addition to the water contained therein. By adjusting the total water content, the melt viscosity of the resulting low melt viscosity polyglycolic acid can be controlled.

More specifically, water is added to moisture-absorbing polyglycolic acid in a wet state taken out by filtration or tilting to adjust the total water content, and then heat drying treatment is performed. There is a certain proportional relationship between the total water content and the melt viscosity value. If the relationship between the total water content and the melt viscosity after heat drying treatment is examined in advance, it is possible to accurately adjust the additional water content to obtain a low melt viscosity polyglycolic acid having a desired melt viscosity value. it can. In order to increase the treatment efficiency in the heat drying treatment step, it is desirable to adjust the total water content within a range of 20% by weight or less, preferably 15% by weight or less. In this case, the lower limit of the total water content is about 3% by weight.

The low melt viscosity polyglycolic acid of the present invention is in a solid form at room temperature (20 ± 15 ° C.), and preferably in a pellet form. This solid form is substantially the same as the solid form of the high melt viscosity polyglycolic acid used as a raw material. The low melt viscosity polyglycolic acid of the present invention has an ester bond in the main chain, and further, there are carboxyl groups formed at the time of synthesis and hydrolysis at both ends. Excellent adhesion to product surface and electroless plating layer surface.

Low melt viscosity polyglycolic acid is a polymer with excellent melt fluidity and adhesion to other materials, and is a polymer with suppressed generation of gas components. Therefore, it is a primary molded product formed from other synthetic resins by injection molding. A thin coating layer containing a fine pattern can be precisely formed on the surface of the substrate. The fine pattern is formed as a fine groove shape. However, since the low melt viscosity polyglycolic acid has crystallinity, when the cross section of the groove is observed, the wall of the groove is formed vertically. Therefore, a conductor circuit with a precise pattern can be formed by plating. Since the low melt viscosity polyglycolic acid has a short solidification time by crystallization, the injection molding cycle can be improved.

The low melt viscosity polyglycolic acid coating layer is not dissolved by the electroless plating solution or the electrolytic plating solution during the plating process. The coating layer is hard to be plated and is difficult to deposit plated metal particles. Since the low melt viscosity polyglycolic acid is decomposable with respect to an alkaline aqueous solution, the coating layer can be removed by treating with an alkaline aqueous solution. There is no need to use an organic solvent to remove the coating layer, and no mechanical peeling work is required. For this reason, in removing the coating layer, the conductor circuit formed by the plating process is not damaged.

The low melt viscosity polyglycolic acid obtained by the production method of the present invention is suitable as a hard-to-plate resin (mask resin) for circuit boards by a two-time molding method. Examples of the primary molded product used in the twice-molding method include, but are not limited to, liquid crystal polymers, thermoplastic polyester resins, polyphenylene sulfide resins, and cyclic olefin resins.

Low melt viscosity polyglycolic acid is injected into a mold with other synthetic resin moldings and used to produce composite moldings in which the synthetic resin molding and polyglycolic acid layer are integrated. It is suitable as a resin material. Low melt viscosity polyglycolic acid has excellent melt flowability and melt stability, so it can be co-extruded with other synthetic resins or by extrusion coating on other synthetic resin films or paper substrates. The present invention can also be used for molding various composite materials.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. The measuring method of physical properties and characteristics in the present invention is as follows.

(1) Method of measuring water content a) Method of measuring total water content A solid polymer sample immersed in water was filtered through a filter, and the weight A of the wet polymer sample remaining on the filter was measured. The wet polymer sample was dried to prepare a dry polymer sample, and the weight B of the dry polymer sample was measured. The total water content was measured by the formula [(AB) / B] × 100.

b) Measuring method of moisture content The moisture content of the polymer was measured using a Karl Fischer moisture meter with a vaporizer [CA-100 manufactured by Mitsubishi Chemical; attached vaporizer VA-100]. Specifically, after wiping off moisture adhering to the surface of the wet polymer, about 2 g of a polymer sample accurately weighed was placed in a vaporizer heated to a temperature of 220 ° C. Dry nitrogen gas was allowed to flow from the vaporizer to the Karl Fischer moisture meter. After the polymer sample was put into the vaporizer, the water vaporized from the polymer sample was introduced into the Karl Fischer liquid in the Karl Fischer moisture measuring device in association with the dry nitrogen gas. The end point was the time when the electric conductivity of the Karl Fischer liquid decreased to +0.1 μg / S from the background by the coulometric titration method.

c) Adhering water The value obtained by subtracting the moisture content from the total water content is called adhering water.

(2) Melting point measurement method The melting point Tm of the polymer was measured using a differential scanning calorimeter TC10A manufactured by METTLER. Measurement was performed in a nitrogen atmosphere while flowing dry nitrogen gas at a rate of 50 ml / min. About 10 mg of a polymer sample was put in an aluminum pan and heated at a temperature increase rate of 50 ° C. to 10 ° C./min, and the melting point Tm was measured.

(3) Measuring method of average molecular weight and degree of dispersion Weight average molecular weight (Mw), number average molecular weight (Mn) and degree of dispersion (Mw / Mn) were measured by gel permeation chromatography (GPC). Showa Denko Co., Ltd. “SHODEX-104” (registered trademark) as a GPC measuring device, Showa Denko Co., Ltd. “HFIP606M” as two columns, 5 mM sodium trifluoroacetate hexafluoroisopropanol solution as eluent, and detector A differential refractive index (RI) detector was used. The calibration of the molecular weight was performed using a polymethacrylic acid standard molecular weight sample.

(4) Melt Viscosity Measurement Method The melt viscosity of a polymer was measured using a Toyo Seiki Capillograph 1-C equipped with a capillary (0.5 mmφ × 10 mmL) as a melt viscosity measurement device. More specifically, about 20 g of the polymer sample is introduced into a measuring apparatus heated to a temperature 10 ° C. higher than the melting point of the polymer sample (Tm + 10 ° C.), and the polymer sample is held at the temperature for 5 minutes. The melt viscosity was measured at 200 sec ⁻¹ . The melt viscosity of the starting polyglycolic acid was measured at a temperature (Tm + 50 ° C.) and a shear rate of 122 sec ⁻¹ .

(5) Measurement method of 3% thermogravimetric decrease temperature The 3% thermogravimetric decrease temperature of the polymer was measured using a thermogravimetric analyzer TC11 manufactured by METTLER. Specifically, a 20 mg polymer sample is placed in a platinum pan, heated in a dry nitrogen atmosphere of 10 ml / min from 50 ° C. to 400 ° C. at a rate of temperature increase of 10 ° C./min, and the weight loss rate during that time is measured. did. The temperature at which the temperature decreased by 3% from the weight of the polymer sample at the start of measurement was defined as a 3% thermogravimetric decrease temperature.

[Comparative Example 1]
As starting materials, a melting point (Tm) of 220 ° C., 270 ° C. (Tm + 50 ° C. = 270 ° C.), a melt viscosity of 506 Pa · s measured at a shear rate of 122 sec ⁻¹ , a weight average molecular weight (Mw) of 192,000, water content Polyglycolic acid with a rate of 30 ppm was used. The polyglycolic acid was melt-extruded in a strand form from an extruder, cooled in water and cut to produce pellets having a uniform shape with an average diameter of 2.8 mm and an average length of 2.7 mm. The 3% thermal weight loss temperature of polyglycolic acid measured using this pellet was 352 ° C.

10 kg of the pellets and 10 liters of ion-exchanged water were put into an autoclave equipped with a stirrer with an internal volume of 25 liters. While maintaining the temperature of the hot water at 55 ° C. by heating the autoclave, the number of stirring blades of the stirrer was maintained at 50 rpm and stirred for 36 hours to perform the hot water immersion treatment.

After the warm water immersion treatment step, filtration was performed to collect wet hygroscopic polyglycolic acid pellets in a wet state with a total water content of 5.8 wt% and a moisture content of 7,726 ppm. The pellets were put in a drier and subjected to heat drying treatment for 6 hours while flowing dry nitrogen heated to 150 ° C. at a flow rate of 300 liters / minute. About the obtained pellet, the measurement of melt viscosity was implemented a total of 3 times (n = 3). The results are shown in Table 1.

[Examples 1 to 5]
The operation was performed in substantially the same manner as in Comparative Example 1 except that the hot water immersion treatment conditions and the heat drying treatment conditions were changed as shown in Table 1. However, in Examples 1 to 4, the raw material polyglycolic acid had a melting point (Tm) of 220 ° C., 270 ° C. (Tm + 50 ° C. = 270 ° C.), a melt viscosity measured at a shear rate of 122 sec ⁻¹ 465 Pa · s, and a weight average Polyglycolic acid having a molecular weight (Mw) of 187,000 and a water content of 30 ppm was used. In Examples 1 to 5, dry air (AI) was used instead of dry nitrogen (N ₂ ). The results are shown in Table 1.

(footnote)
(1) PGA: polyglycolic acid (2) Mw: weight average molecular weight (3) N ₂ : dry nitrogen (4) AI: dry air

<Discussion>
As is apparent from the results in Table 1, when the temperature of hot water is 55 ° C. (Comparative Example 1), it is necessary to perform the hot water immersion treatment process over 36 hours. Further, when the rotational speed of the stirring blade is as small as 50 rpm (Comparative Example 1), the dispersion of the melt viscosity within the same lot of the low melt viscosity polyglycolic acid becomes large, and the difference between the maximum value and the minimum value is large. Becomes larger.

On the other hand, it can be seen that by setting the temperature of the hot water to 60 ° C. or higher, and further to 70 ° C. or higher, the processing time in the hot water immersion treatment process can be significantly shortened (Examples 1 to 5). It can be seen that when the rotation speed of the stirring blade is increased to 100 rpm or more, preferably 150 rpm or more, the dispersion of the melt viscosity within the same lot of the low melt viscosity polyglycolic acid is reduced (Examples 1 to 5). Furthermore, according to the production method of the present invention (Examples 1 to 5), a low melt viscosity polyglycolic acid which has a 3% thermal weight loss temperature maintained at a high level and has a low moisture content and is sufficiently dried is obtained. Can be obtained efficiently.

[Examples 6 to 8 and Comparative Example 2]
Using the same pellets prepared in Comparative Example 1, the temperature of the hot water was 100 ° C. (Example 6), 80 ° C. (Example 7), 70 ° C. (Example 8), and 55 as shown in Table 2. The temperature was changed to 0 ° C. (Comparative Example 2), the number of revolutions of the stirring blade was set to 200 rpm, and hot water immersion treatment was performed. Table 2 shows the measurement results of treatment time, weight average molecular weight (Mw), number average molecular weight (Mn), and dispersity (Mw / Mn).

After the hot water immersion treatment step, filtration was performed to collect wet hygroscopic polyglycolic acid pellets. Each of these pellets was put in a drier and heat-dried for 6 hours while flowing dry air heated to 150 ° C. at a flow rate of 300 l / min. The results are shown in Table 3.

[Comparative Example 3]
An autoclave was charged with 500 g of glycolic acid [Wako Pure Chemical Industries, Ltd.], heated at 170 ° C. to 200 ° C. over 2 hours with stirring at normal pressure, and subjected to a polycondensation reaction while distilling the produced water. . Next, the internal pressure of the can was reduced to 5.0 kPa and heated at 210 ° C. for 4 hours to distill off low-boiling components such as unreacted raw materials. The polycondensation product was crystallized by cooling, taken out from the autoclave, and pulverized to obtain powdered polyglycolic acid. The melting point Tm of this polyglycolic acid was 218 ° C. Using the polyglycolic acid, the melt viscosity of the polyglycolic acid at a temperature (Tm + 10 ° C. = 228 ° C.) and a shear rate of 1,200 sec ⁻¹ was measured and found to be 10 Pa · s. It was 252 degreeC when the 3% thermogravimetric reduction temperature of this polyglycolic acid was measured. The results are shown in Table 3.

<Discussion>
As is clear from the results in Table 2, when the temperature of the hot water is set to 100 ° C. (Example 6), it is estimated that the hydrolysis reaction proceeds from the surface of the pellets in the hot water immersion treatment process. While the weight average molecular weight (Mw) of polyglycolic acid falls remarkably, the dispersion degree (Mw / Mn) tends to become broad. On the other hand, when the temperature of warm water is set to 80 ° C. (Example 7), 70 ° C. (Example 8), and 55 ° C. (Comparative Example 2), the degree of hydrolysis in the warm water immersion treatment step is small. In addition, moisture-absorbing polyglycolic acid pellets with a sharp degree of dispersion can be obtained. However, when the temperature of the hot water is set to 55 ° C. (Comparative Example 2), a long time is required to sufficiently absorb the inside of the pellet, which is not efficient.

<Discussion>
As is apparent from the results in Table 3, the moisture-absorbing polyglycolic acid soaked in warm water at 100 ° C. has a high degree of dispersion because the hydrolysis reaction proceeds rapidly at the surface portion, which is heated and dried. It can be seen that the 3% thermal weight loss temperature of the low melt viscosity polyglycolic acid obtained by the treatment decreases (Example 6).

The polyglycolic acid having a low melt viscosity obtained by the method for producing a polyglycolic acid having a low polymerization degree at the time of synthesis has a 3% thermal weight loss temperature of 252 ° C., and has a high content of low molecular weight substances. A large amount of gas components are easily volatilized (Comparative Example 3).

On the other hand, when the temperature of the hot water is set to 55 to 80 ° C. (Examples 7 to 8 and Comparative Example 2), the 3% thermal weight loss temperature is maintained at a high level and the melt viscosity is lowered. Polyglycolic acid can be obtained. However, since the comparative example 2 requires a long time for the hot water immersion treatment as described above, it is not efficient.

[Example 9]
Using the polyglycolic acid pellets prepared in Comparative Example 1, the hot water temperature was set to 70 ° C., the rotation speed of the stirring blade was set to 200 rpm, and the treatment time was set to 5 hours, and the hot water immersion treatment step was performed. Thereby, moisture-absorbing polyglycolic acid pellets in a wet state with a water content of 8,910 ppm and a total water content of 4.12% by weight were recovered. The moisture-absorbing polyglycolic acid pellets were put in a drier and heat-dried for 6 hours while flowing dry air heated to 150 ° C. at a flow rate of 300 liters / minute. As a result, a low melt viscosity polyglycolic acid having a water content of 46.5% by weight and a melt viscosity of 24 Pa · s was obtained. The results are shown in Table 4.

[Examples 10 and 11]
In Example 9, water was added to wet hygroscopic polyglycolic acid pellets to adjust the total water content. Then, the heat drying process was performed by the same operation as Example 9. The results are shown in Table 4.

(* 1) After the warm water immersion treatment step of Example 9, water was added to the wet pellets to adjust the total water content.

<Discussion>
As apparent from the results in Table 4, after the hot water immersion treatment step, the melt viscosity is further increased after the heat drying treatment step by adding water to the wet hygroscopic polyglycolic acid pellets to adjust the total water content. It can be seen that reduced low melt viscosity polyglycolic acid pellets are obtained. The degree of decrease in melt viscosity is approximately proportional to the total water content. Therefore, if the relationship between the total water content and the melt viscosity value is examined in advance, the melt viscosity value of the low melt viscosity polyglycolic acid can be precisely determined by simply adding water and adjusting the total water content of the pellets. Can be controlled.

The low melt viscosity polyglycolic acid of the present invention can precisely mold a thin film with a fine pattern on the surface of another synthetic resin molded product by injection molding, has excellent plating resistance, and is an alkaline aqueous solution. Since it is soluble, it can be used as, for example, a mask resin for MID (three-dimensional injection molded circuit components). The low melt viscosity polyglycolic acid of the present invention can be used in a wide range of technical fields that are required to be excellent in melt flowability during molding, precision moldability, adhesion to other materials, gas barrier properties, and the like. .

Claims (15)

1. Steps 1 and 2 below
   (1) A polyglycolic acid having a melt viscosity exceeding 100 Pa · s measured at a temperature 50 ° C higher than the melting point Tm of the polyglycolic acid (Tm + 50 ° C) and a shear rate of 122 sec ^-1 is 60-100 ° C in a predetermined solid form. Hot water immersion treatment step 1 for obtaining moisture-absorbing polyglycolic acid having a water content of 1,000 ppm or more by immersing in warm water and absorbing moisture while maintaining its solid form;
   (2) The moisture-absorbing polyglycolic acid is heated and dried at a temperature in the range from 60 ° C. to 5 ° C. lower than the melting point of the polyglycolic acid (Tm−5 ° C.) while maintaining its solid form. The melt viscosity measured at a temperature 10 ° C. higher than the melting point of glycolic acid (Tm + 10 ° C.) and a shear rate of 1,200 sec ⁻¹ is 150 Pa · s or less, the 3% thermal weight loss temperature is 280 ° C. or more, and the water content is 500 ppm. Heat drying treatment step 2 for obtaining the following low melt viscosity polyglycolic acid;
   A process for producing a low melt viscosity polyglycolic acid comprising:
2. The process according to claim 1, wherein the polyglycolic acid has a melt viscosity in the range of more than 100 Pa · s and 3,000 Pa · s or less.
3. The manufacturing method according to claim 1, wherein the predetermined solid shape is a shape of a pellet or a particle.
4. The production method according to claim 1, wherein in the step 1, the mixing ratio of the high melt viscosity polyglycolic acid having a predetermined shape and warm water is within a range of 1:10 to 10: 5 by weight.
5. The method according to claim 1, wherein in the step 1, the polyglycolic acid is immersed in warm water of 60 to 90 ° C in a predetermined solid form to absorb moisture while maintaining the solid form.
6. 2. The production method according to claim 1, wherein in step 1, a hygroscopic polyglycolic acid having a dispersity (Mw / Mn) of 2.15 or less expressed by a ratio of a weight average molecular weight (Mw) to a number average molecular weight (Mn) is obtained. .
7. The manufacturing method of Claim 1 which obtains the moisture absorption polyglycolic acid whose water content of polyglycolic acid is 5,000 or more in a warm water immersion treatment process.
8. In the step 1, the polyglycolic acid is immersed in warm water in the form of pellets to absorb moisture while maintaining the pellet shape, thereby obtaining a hygroscopic polyglycolic acid. Next, in the step 2, the hygroscopic polyglycolic acid is obtained. The manufacturing method of Claim 1 which heat-drys glycolic acid, maintaining the pellet shape, and obtains low melt viscosity polyglycolic acid.
9. In the step 1, the polyglycolic acid is charged in a pellet form into a stirring tank provided with a stirrer and immersed in warm water, and the stirrer blade speed of the stirrer is 1 to 500 rpm. By stirring for 15 hours and absorbing moisture while maintaining the pellet shape, a hygroscopic polyglycolic acid is obtained, and then in step 2, the hygroscopic polyglycolic acid is heated and dried while maintaining the pellet shape, The process according to claim 1, wherein low melt viscosity polyglycolic acid is obtained.
10. In the step 2, water is added to the hygroscopic polyglycolic acid to adjust the total water content including the amount of water contained in the solid polyglycolic acid and the amount of water adhering to the surface, followed by drying by heating. The process according to claim 1, wherein the melt viscosity of the low melt viscosity polyglycolic acid is controlled.
11. 11. The production method according to claim 10, wherein in the step 2, water is added to the hygroscopic polyglycolic acid to adjust the total water content within a range of 3 to 20% by weight, followed by heat drying.
12. In step 2, the hygroscopic polyglycolic acid is heated by a method of flowing an inert gas or air heated to a temperature in the range from 60 ° C. to a temperature 5 ° C. lower than the melting point of the polyglycolic acid (Tm−5 ° C.). The manufacturing method of Claim 1 which dries.
13. 13. The production method according to claim 12, wherein heated inert gas or air is allowed to flow at a flow rate of 0.1 to 30,000 liters / minute.
14. The production method according to claim 1, wherein in the step 2, the heat drying treatment is performed within a range of 1 to 200 hours.
15. In Step 2, a 3% thermogravimetric decrease temperature is within a range of 1 to 150 Pa · s at a melt viscosity measured at a temperature 10 ° C. higher than the melting point of polyglycolic acid (Tm + 10 ° C.) and a shear rate of 1,200 sec ^−1. The production method according to claim 1, wherein a low melt viscosity polyglycolic acid having a water content in the range of 280 to 355 ° C and a water content of 2 to 500 ppm is obtained.