JPH0812621A - Purification of lactic acid ester - Google Patents

Abstract

PURPOSE:To provide a process for the purification of a lactic acid ester useful as a safe solvent for a photoresist resin having high dissolving power of the resin. CONSTITUTION:A lactic acid ester produced by a fermentation process is purified by distilling the ester after treating with an activated carbon to lower the absorption of UV of <=300nm wavelength. This process gives a high-purity lactic acid ester having UV absorption at 280nm decreased to <=1, a purity of >=99.9% and a low metal content (<=10ppb).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for purifying a lactate ester. More specifically, the present invention relates to a method for purifying a lactic acid ester useful as a solvent for a photoresist, which comprises subjecting a lactic acid ester produced from a lactic acid produced by a fermentation method as a raw material to active carbon treatment and then performing distillation purification.

[0002]

2. Description of the Related Art Conventionally, as a photoresist resin solvent used in a wide range of fields such as semiconductor devices, printed wiring boards, and printed boards manufactured by utilizing the lithography technique, ethyl cellosolve acetate (hereinafter referred to as E
CA), ethyl pyruvate, diglyme, methyl cellosolve acetate, etc. have been used.
In particular, ECA has been dominated by its excellent performance as a photoresist solvent.

[Problems to be Solved by the Invention]

However, since it was announced that reproductive function and other disorders would occur when ECA is absorbed into the body, there has been a strong demand from the industry for the immediate emergence of ECA alternative solvents. Under such circumstances, lactate ester, particularly ethyl lactate, has been investigated as a solvent for photoresist resin because of its good solubility of resist resin, high safety, etc. as an ECA substitute solvent.

However, the disadvantage of lactic acid ester (hereinafter referred to as fermented lactic acid ester) produced by using lactic acid produced by the fermentation method (hereinafter referred to as fermented lactic acid) as a raw material is that trace amounts of impurities (such as acrylic acid ester) Due to
It absorbs light in the so-called deep UV (ultraviolet) region having a wavelength of 300 nm or less. The minute amount of impurity components that cause the UV absorption cannot be substantially removed by conventional purification means (for example, distillation purification).

For example, fermented lactic acid ester is a sugar (sugar beet,
Fermented lactic acid produced by fermenting corn, etc.) is esterified with alcohol (methanol, ethanol, butanol, etc.). The fermented lactic acid ester produced in this way, for example fermented ethyl lactate, has a U of 280 nm.
V absorption is 2.0 or more, and may reach 3.0 or more in some cases.

On the other hand, there is an increasing demand for higher density and higher integration of semiconductor devices and higher resolution of pattern profiles for printed wiring boards and printed boards. Along with this, with respect to the lithography technique, fine processing and sophistication with a resolution of 0.5 μm or less by so-called half micron lithography technique are required. Therefore, as the light with which the resist is irradiated, for example, a low pressure mercury lamp or a deep UV having an excimer laser as a light source is used, and the wavelength at this time is 300 nm or less.

Therefore, when the fermented lactate ester is purified by a conventional purification method and used as a photoresist solvent, there arises a problem that the amount of radiation to be irradiated increases or that light does not reach a deep portion. However, problems such as poor performance of semiconductor devices due to impurities and contained metals occur. Therefore, as a solvent for photoresist, for example, 28
There is a need for a low-metal lactate ester having a UV absorption of 0 nm of 1.0 or less, preferably 0.6 or less, and a small amount of impurities. The present invention solves these problems. That is, an object of the present invention is to provide a method for purifying a fermented lactic acid ester for reducing UV absorption of 300 nm or less to a substantially negligible level and obtaining a lactic acid ester having few impurities and suitable for a photoresist having a low metal content. It is to be.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the fermented lactic acid ester is treated with activated carbon and then purified by distillation.
The inventors of the present invention have found that a lactate ester having a UV absorption of 00 nm or less and a reduced UV absorption can be obtained, and arrived at the present invention.
That is, the present invention is a method for purifying a lactic acid ester, which comprises distilling and purifying a fermented lactic acid ester, which is previously treated with activated carbon to reduce UV absorption at 300 nm or less and then distilled.

Examples of the fermented lactic acid ester used in the present invention include methyl lactate, ethyl lactate, butyl lactate, propyl lactate and the like. The activated carbon used in the present invention is not particularly limited, but its average pore diameter (D) is 100.
Those below Å are effective, and those below 50 Å are particularly effective. When the average pore size is 100 Å or more, the effect is slightly reduced. Raw material for activated carbon (Peat, palm shell, wood, lignite, call, etc.), activation method (chemical activation, steam activation)
And the influence of the shape (granular coal, powdered coal) on the treatment effect is substantially small.

The activated carbon treatment method according to the method of the present invention is
It can be carried out in the same manner as the usual activated carbon treatment.
Generally, it is carried out by mixing and stirring the lactic acid ester and the activated carbon for several minutes to about 10 hours and then filtering, or by passing the lactic acid ester through a fixed bed packed with activated carbon in a column. In either method, in order to avoid elution of the components in the activated carbon, the activated carbon treatment is preferably carried out at room temperature or under slight heating. In the case of powdered activated carbon, the method of mixing and stirring is generally used, and the activated carbon is usually 0.1 to 20 wt%, generally 0.5 to 10 wt% with respect to the lactic acid ester to be treated.
Is added and stirred for several minutes to about 10 hours, and then filtered to remove the activated carbon. In the case of granular activated carbon, a fixed bed method is suitable, and the activated carbon is usually added to the lactate ester to be treated in an amount of 0.3
-10 wt%, generally 0.5-5 wt% is packed in a column and contacted through 0.5-10 volume / hour of lactate ester of activated carbon amount (volume). By the activated carbon treatment, UV absorption of lactic acid ester at 280 nm was usually 2 to 4, but it is reduced to 1 or less. In the case of the mixed stirring system, the activated carbon is removed by filtration before distillation, but in the case of the fixed bed system, no particular filtration is necessary, and the effluent can be immediately distilled.

Since the resist solvent is required to have a high degree of UV absorption as well as a high-purity product, for example, a purity of 99.9% or more, the distillation operation after the treatment with activated carbon is also an important step. It is essential to suppress the formation of alcohol, lactic acid by decomposition and lactic acid dimer by condensation as much as possible. Therefore, the distillation in the method of the present invention is carried out at a temperature of 100 ° C. or lower and a pressure of 1 due to the nature of the lactate ester.
It is preferable to carry out under the condition of 00 torr or less. When the distillation temperature is 100 ° C. or higher, the lactate ester is decomposed or condensed, and it is difficult to obtain a high-purity product (99.9% or higher). Although addition of a stabilizer or the like is effective, basically, suppression of decomposition by temperature control is most effective.

[0012]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples.

[Examples] Plant-based granular charcoal (Norito Japan, PK 0.
(6-2 mm) 100 ml was packed in a glass column, and fermented ethyl lactate (purity 98.1%, UV absorption at 280 nm of 3.710) 3 liters was inserted at a rate of 500 ml / h, and treated with activated carbon. 280 of ethyl lactate after treatment
The UV absorption at nm was 0.414. Next, this ethyl lactate (2 liters) was heated at a temperature of 90 in a distillation column corresponding to 20 plates.
Purity 99.987%, UV absorption at 280 nm of 0.9 by distillation under conditions of ˜95 ° C. and pressure of 100˜110 torr.
1.8 liters of 225 ethyl lactate was obtained. The metal content is Na: 11 ppb, K: 0.5 ppb, F
e: It was found to be a low metal ethyl lactate at 1.8 ppb.

[0013]

[Example 2] Activated carbon granular carbon (RAX, manufactured by Nippon Norit Co., Ltd.)
100 ml of -1) was packed in the same glass column as in Example-1, and fermented ethyl lactate (purity 98.6%, 280 nm
UV absorption of 2.874) 3 liters 400ml / hr
It was inserted at the speed of and activated carbon treatment was performed. The UV absorption of ethyl lactate after treatment at 280 nm was 0.524. Next, this ethyl lactate (1 liter) was placed in the same distillation column as in Example 1 at a temperature of 80 to 85 ° C. and a pressure of 450 to 50 torr.
Distilled under the conditions of 99.992% purity, 280nm
UV absorption of 0.715 l of ethyl lactate of 0.315 was obtained. The metal content is Na: 1.0, K: 0.9, F
e: 1.1, Cu: 0.4, Mn: 1.2 (ppb) and it was found to be a low metal ethyl lactate.

[0014]

[Example 3] Plant-based powdered coal (SX- manufactured by Nippon Norit Co., Ltd.)
40 g of 1) was charged into a 1 liter four-necked flask equipped with a stirrer and a thermometer, 800 g of the same fermented ethyl lactate as in Example-2 was charged, and the mixture was stirred and mixed at room temperature (20 to 25 ° C.) for 6 hours. Then, adsorption treatment was performed. The UV absorption at 280 nm of the treated ethyl lactate was 0.308. Next, this ethyl lactate (0.7 liter) was placed in the same distillation column as in Example 1 at a temperature of 90 to 95 ° C. and a pressure of 70 to 100 torr.
Distilled under the condition of r, purity 99.978%, 280n
m UV absorption 0.273 liter of ethyl lactate 0.273 was obtained. The metal content is Na: 0.8, K: 0.0.
6, Fe: 1.0, Cu: 0.5, Mn: 0.8, Mg:
It was found to be ethyl lactate having a low metal content of 0.4 and Ca: 1.2 (ppb).

[0015]

[Example 4] Coal-based granular coal (GRA manufactured by Nippon Norit Co., Ltd.
50 g of (NULAR DARCO) was charged into the same four-necked flask as in Example-3, 800 g of the same fermented ethyl lactate as in Example-1 was charged, and the mixture was stirred and mixed at room temperature (20 to 25 ° C.) for 10 hours, and then adsorbed. Processed. The UV absorption of ethyl lactate after treatment at 280 nm was 0.647.
Next, the treated ethyl lactate (0.7 liter) was used in Example-1.
In the same distillation column as above, temperature 55 ~ 60 ℃, pressure 15 ~ 30t
Distilled under the conditions of orr to obtain a purity of 99.995%, 28
The UV absorption at 0 nm was 0.528. The metal content is Na: 2.1, K: 1.2, Fe: 2.8, C
A: 1.0, Mn: 0.8, Cu: 0.9 (ppb), and it was found to be a low metal ethyl lactate.

[0016]

[Comparative example]

[Comparative Example 1] The same fermented ethyl lactate (1 liter) as in Example-1 was used in the distillation column used in Example-1 at a temperature of 80-8.
Distillation was performed under the conditions of 5 ° C. and a pressure of 45 to 50 torr to obtain 0.85 liter of ethyl lactate having a purity of 99.991%, a UV absorption of 280 nm of 3.518. The UV absorption at 280 nm is hardly reduced by distillation purification alone.

[0017]

Comparative Example 2 1 liter of ethyl lactate (UV absorption 0.408 at 280 nm) obtained by treating the same fermented ethyl lactate (3 liters) as in Example 1 with activated carbon under the same conditions as in Example 1 was used. Using the same distillation column as in No. 1, the temperature of 110
˜120 ° C., pressure 130-140 torr, distilled under conditions of 99.08% purity, UV absorption at 280 nm.
0.83 liter of 210 ethyl lactate was obtained. It was found that the purity did not reach 99.9%.

[0018]

According to the method of the present invention, high purity (99.9)
It is possible to obtain ethyl lactate having a UV absorption of 1% or less and a UV absorption of 1% or less. According to the method of the present invention, in addition to high purity and reduced UV absorption, low metal products
(Na, K, Fe, Ca, Mn and other metals are 10
ppb or less) can be obtained.

Claims (2)

[Claims] 1. A method for purifying a lactic acid ester, which comprises subjecting a lactic acid ester produced from a lactic acid produced by a fermentation method as a raw material to a treatment with activated carbon, followed by distillation and purification. 2. The method for purifying a lactic acid ester according to claim 1, wherein the distillation purification is carried out at 100 ° C. or lower.