EP0913464A1

EP0913464A1 - Process for cleaning articles

Info

Publication number: EP0913464A1
Application number: EP97924236A
Authority: EP
Inventors: Toshiro Yamada; Mitsuru Sugawara; Kuniaki Goto
Original assignee: Nippon Zeon Co Ltd
Current assignee: Zeon Corp
Priority date: 1996-05-30
Filing date: 1997-05-28
Publication date: 1999-05-06
Also published as: KR20000016203A; EP0913464A4; WO1997045521A1

Abstract

In a cleaning process comprising (1) a step of cleaning an article with a cleaning solvent predominantly comprised of a hydrocarbon, (2) a step of rinsing the article having attached thereto the cleaning solvent, with a rinsing solvent predominantly comprised of a hydrofluorocarbon, and (3) a step of separating into two layers the hydrocarbon-containing rinsing solvent discharged from the rinsing step (2); a cyclic hydrofluorocarbon, in which the number of fluorine atoms is larger than the number of hydrogen atoms, is used as the rinsing solvent.

Description

Technical Field

This invention relates to a process for cleaning articles such as metal, glass, plastic and other articles which have been smeared with oils, fats, greases, fluxes, dirt from the hands or other dirty substances in a precision machine industry, an optical machine industry, an electronic industry, a plastic industry and other industries.

Background Art

Production and use of chlorine-containing general-purpose cleaning solvents such as CFC 113 (chlorofluorocarbon) and trichloroethane have been prohibited under the regulation over the world to protect the stratospheric ozone layer. Therefore, researches of cleaning processes using alternative solvents are now being widely pursued. For example, there have been proposed a cleaning process using water or a water-soluble solvent, and cleaning process using a hydrocarbon or a chlorine-or fluorine-containing solvent, the use of which is not regulated.
Further, a co-solvent system has been proposed wherein a cleaning solvent having a cleaning function such as a hydrocarbon, an alcohol or silicone is used in combination with a rinsing solvent which has a low-boiling point and a good drying property and is incombustible, such as a perfluorocarbon (PFC), a hydrochlorofluorocarbon (HCFC) or a hydrofluorocarbon (HFC). For example, a cleaning process is described in WO 95/05448 wherein cleaning is effected by using an organic solvent selected from hydrocarbons, higher alcohols, ethers and organic silicones, and then, rinsing is effected by using a cyclic hydrofluorocarbon having 4 to 5 carbon atoms.
In the cleaning process based on the co-solvent system, in order to reduce the running cost and keep good cleaning performance over a long period, it is necessary that a waste mixed solvent is separated into the cleaning solvent having a cleaning function and the solvent for rinsing and drying, which are reused for cleaning. For the separation of the waste mixed solvent into the respective ingredients, it is conventionally conducted to distill the mixed solvent, but, the separation of the waste mixed solvent into a rinsing solvent having a low boiling point, a cleaning solvent having a high boiling point and the dirty substances by distillation is complicated, the distillation equipment is expensive and the running cost is high.
A cleaning process has been proposed in Japanese Unexamined Patent Publication (hereinafter abbreviated to "JP-A") No.H7-197092 wherein, a cleaning solvent selected from hydrocarbons, alcohols, esters, ketones and glycol ethers, is used in combination with a rinsing solvent selected from hydrofluorocarbons, and a waste mixed solvent is subjected to a phase separation utilizing difference in specific gravity whereby the mixed solvent is separated into a hydrofluorocarbon and, for example, a hydrofluorocarbon which is reused for vapor drying. As specific examples of the hydrofluorocarbon used as a rinsing solvent, straight-chain hydrofluorocarbons such as 1,1,2,3-tetrafluoropropane and 1,1,1,2,2,3,4,5,5,5-decafluoropentane are recited. However, the proposed cleaning process has problems such that, in the case where a hydrocarbon is used as the cleaning solvent, the cleaning performance of the hydrocarbon is improved only to a limited extent although a straight-chain hydrofluorocarbon rinsing solvent is used in combination with the cleaning solvent; and further, when the mixed solvent is subjected to a phase separation for recovery, the hydrocarbon layer contains a salient amount of the expensive hydrofluorocarbon and thus the process is not economical.
Another cleaning process has been proposed in JP-A H4-272194 wherein, cleaning is effected by using a hydrocarbon solvent, rinsing is effected by using a perfluorocarbon, and then, the mixed solvent is subjected to a phase separation utilizing the specific gravity difference for recovery and reuse of the perfluorocarbon. This process is not advantageous because a perfluorocarbon has a poor rinsing power.

Disclosure of Invention

In view of the foregoing, the object of the present invention is to provide a process for cleaning an article whereby the following steps (1), (2) and (3) can be conducted with an enhanced efficiency and a reduced running cost: (1) a step of cleaning an article with a cleaning solvent predominantly comprised of a hydrocarbon, (2) a step of rinsing with a hydrofluorocarbon the article having attached thereto the cleaning solvent, and (3) a step of subjecting the hydrocarbon-containing rinsing solvent discharged from the step (2) to a phase separation.
The inventors made extensive researches and found that, by using as a rinsing solvent a hydrofluorocarbon having a cyclic molecular structure and in which the number of fluorine atoms is larger than the number of hydrogen atoms in the cleaning process comprising the above-mentioned cleaning step (1), rinsing step (2) and separation step (3), the following benefits (i), (ii) and (iii) are achieved: (i) the rinsing effect on the hydrocarbon is very high, (ii) the hydrocarbon layer separated by the phase separation contains only a greatly reduced amount of the hydrofluorocarbon, and (iii) the hydrofluorocarbon layer separated by the phase separation contains only a minor amount of the hydrocarbon, and thus, can be reused as rinsing solvent and vapor-cleaning solvent. Based on these findings, the present invention has been completed.
In accordance with the present invention, there is provided a process for cleaning an article comprising the steps of (1) a cleaning step of placing an article in contact with a cleaning solvent predominantly comprised of a hydrocarbon, (2) a rinsing step of placing the article taken from the cleaning step (1) and having attached thereto the cleaning solvent, in contact with a rinsing solvent predominantly comprised of a hydrofluorocarbon, and (3) a separation step of separating into two layers the hydrocarbon-containing rinsing solvent discharged from the rinsing step (2) by a phase separation, characterized in that the hydrofluorocarbon used is a cyclic compound, in which the number of fluorine atoms is larger than the number of hydrogen atoms.

Brief Description of the Drawings

Figure 1 is a diagrammatic sectional view illustrating an example of a cleaning apparatus used in the cleaning process of the present invention.

Best Mode for Carrying Out the Invention

Article to Be Cleaned

The cleaning process of the present invention is applicable for cleaning articles smeared with dirty substances (such articles are hereinafter abbreviated to "articles").
The articles are not particularly limited, and include, for example, articles made of metals, ceramics, glass, plastics, elastomers and other materials and used in a precision machine industry, a metal machining industry, an optical machine industry, a plastic industry and other industries. As specific examples of the articles, there can be mentioned automobile parts such as bumpers, transmission gears, transmission parts and radiator parts, electronic and electrical parts such as printed circuit boards, IC parts, lead frames, motor parts and capacitors, precision machine parts such as bearings, gears, engineering plastic toothed gears, clock and watch parts, camera parts and optical lenses, large-size machine parts such as printing machines, blades for a printing machine, printing rolls, rolled articles, construction machines, glass substrates and large-size heavy machine parts, and daily necessities such as tableware.
The substances causing smears on articles include, for example, oils such as cutting oil, quenching oil, rolling oil, lubricating oil, machining oil, press-machining oil, punching oil, drawing oil, assembling oil and inking oil, greases, waxes, adhesives, fats and oils, mold releasing agents, dirt from the hands, soldering fluxes, resists and solder pastes.

(1) Cleaning step

In the first step of the process of the present invention, an article is cleaned with a cleaning solvent predominantly comprised of a hydrocarbon.
The hydrocarbon used includes, for example, straight-chain saturated, straight-chain unsaturated, cyclic saturated and cyclic unsaturated aliphatic hydrocarbons, and aromatic hydrocarbons. Of these, aliphatic hydrocarbons are preferable. Straight-chain saturated and cyclic unsaturated hydrocarbons are especially preferable. A suitable number of carbon atoms in the hydrocarbon varies depending upon the particular cleaning type and use of article, but the number of carbon atoms is usually in the range of 5 to 30, preferably 8 to 20 and more preferably 10 to 15.
As specific examples of the hydrocarbon, there can be mentioned saturated straight-chain aliphatic hydrocarbons such as pentane, hexane, heptane, octane, isooctane, nonane, decane, isodecane, undecane, dodecane, isododecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane and isooctadecane; saturated cyclic hydrocarbons such as cyclopentane, methyl-cyclopentane, cyclohexane, methyl-cyclohexane, cyclodecane, methyl-cyclodecane, cyclododecane, decalin and norbornane; unsaturated straight-chain aliphatic hydrocarbons such as heptene, heptadiene, octene, octadiene, nonene, nonadiene, decene, decadiene, undecene, dodecene, dodecadiene, tridecene, tridecadiene, tetradecene, tetradecadiene, octadecene, octadecadiene and isoprene dimer; unsaturated cyclic hydrocarbons such as terpenes including α -pinene, β-pinene, γ-terpinene, δ-3-carene, dipentene and terpinene; and aromatic hydrocarbons such as toluene. Of these, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, limonene and dipentene are preferable. These hydrcarbons may be used alone or in combination. As examples of commercially available hydrocarbon cleaning solvents, there can be mentioned normal paraffin series, Isozole series, Isolane series (these three types of series are supplied by Nippon Petrochemicals Co.), #0 to #5 solvents, Teclean series (these two types of series are supplied by Nippon Oil Co.), and NS clean series (supplied by Nippon Mining & Petrochemical Co.).
The cleaning solvent used in the present invention is predominantly comprised of the above-mentioned hydrocarbon. Namely, the cleaning solvent may either be composed only of the hydrocarbon, or may have incorporated therein various additives such as cutting oil, lubricating oil, machining oil and press-machining oil.
As the procedure of cleaning an article, a conventional cleaning procedure can be adopted wherein the article is placed in contact with the cleaning solvent. More specifically procedures such as hand wiping, dipping, spraying and showering can be adopted. Of these, dipping is preferable. When a dipping procedure is employed, a physical means such as ultrasonic vibration, rocking, stirring and brushing may be additionally adopted. The temperature of the cleaning solvent is suitably chosen depending upon the particular nature of the article, but is usually in the range of from room temperature to the boiling point, preferably from 40°C to the boiling point and more preferably from 50°C to the boiling point.

(2) Rinsing Step

The cleaning process of the present invention is characterized in that, subsequently to the above-mentioned cleaning step, the article having attached thereto the hydrocarbon cleaning solvent is subjected to a rinsing using a rinsing solvent predominantly comprised of a cyclic hydrofluorocarbon. The use of a cyclic hydrofluorocarbon is advantageous over a straight-chain hydrofluorocarbon and a perfluorocarbon in that a cyclic hydrofluorocarbon exhibits an enhanced effect for removing the hydrocarbon cleaning solvent. This effect is prominently manifested when the articles are continuously cleaned.
The rinsing power of a cyclic hydrofluorocarbon will be explained below.

(i) Solubility of Hydrocarbon

The solubility of a hydrocarbon in a cyclic hydrofluorocarbon is sharply increased by heating, and is higher than those of a straight-chain hydrofluorocarbon and perfluorocarbon. Most cyclic hydrofluorocarbons have a boiling point higher than that of straight-chain hydrofluorocarbons having the same number of carbon atoms as that of the cyclic hydrofluorocarbons. Thus, rinsing with a cyclic hydrofluorocarbon can be conducted at a higher temperature, and the solubility of a hydrocarbon in the cyclic hydrofluorocarbon can be more enhanced.

(ii) Operation of Rinsing Solvent in Uniform State

If a perfluorocarbon is used as a rinsing solvent, a hydrocarbon solvent separated from the article is subjected to phase separation on the perfluorocarbon rinsing solvent because the perfluorocarbon and the hydrocarbon are almost incompatible. Where a hydrocarbon upper layer is formed on a perfluorocarbon lower layer, when the dipped article is taken up, the hydrocarbon is again attached to the article with the result of reduction in rinsing effect. A hydrocarbon also has poor compatibility with a straight-chain hydrofluorocarbon, and therefore, when a rinsing is repeated, a hydrocarbon upper layer is easily formed and the rinsing effect is reduced.
In contrast, a hydrocarbon has good compatibility with a cyclic hydrofluorocarbon, and therefore, even where a rinsing of articles is repeated for a long period, the rinsing liquid can be kept at a uniform state. By recovering a part of the used rinsing solvent or continuously substituting a part of the rinsing solvent by a fresh rinsing solvent, the rinsing can be continuously conducted over a long period.
The cyclic hydrofluorocarbon used in the present invention is a cyclic compound having carbon, hydrogen and fluorine atoms and characterized in that the number of fluorine atoms is larger than the number of hydrogen atoms. If the number of fluorine atoms is too small, the difference in specific gravity between the cyclic hydrofluorocarbon and the hydrocarbon is too small and the phase separation into two layers becomes difficult. If a hydrogen atom is not contained, compatibility between the two solvents becomes poor and the rinsing effect is reduced. When the number of hydrogen atoms in the cyclic hydrofluorocarbon is in the range of from 1 to 5, a good effect of rinsing the hydrocarbon can be obtained, and undesirable contamination with the hydrocarbon can be minimized as the phase separation into the two layers occurs. The number of hydrogen atoms is preferably in the range of from 1 to 3, and more preferably 2. When the number of carbon atoms is in the range of from 4 to 10, the solubility of the hydrocarbon at the rinsing step and that at the phase separation are well balanced. The number of carbon atoms is preferably in the range of from 4 to 6 and more preferably 5.
As specific example of the cyclic hydrofluorocarbon, there can be mentioned 1,1,2,2-tetrafluorocyclobutane, 1,2,3,4,4-pentafluorocyclobutane, 1,1,2,2,3,4-hexafluorocyclobutane, heptafluorocyclobutane, 1,1,2,2,3-pentafluorocyclopentane, 1,1,2,2,3,3-hexafluorocyclopentane, 1,1,2,2,3,4,5-heptafluorocyclopentane, 1,1,2,3,3,4,5-heptafuluorocyclopentane, 1,1,2,2,3,3,4,5-octafluorocyclopentane, 1,1,2,2,3,4,4,5-octafluorocyclopentane, 1,1,2,2,3,3,4,4-octafluorocyclopentane, nonafluorocyclopentane, 1,1,2,2,3,3,4,5-octafluorocyclohexane, 1,1,2,2,3,3,4,4,5,6-decafluorocyclohexane, tetradecafluorodecalin and hexafluorodecalin. Of these, 1,2,3,4,4-pentafluorocyclobutane, 1,1,2,2,3,4-hexafluorocyclobutane, heptafluorocyclobutane, 1,1,2,2,3,4,5-heptafluorocyclopentane, 1,1,2,3,3,4,5-heptafluorocyclopentane, 1,1,2,2,3,3,4,5-octafluorocyclopentane, 1,1,2,2,3,3,4,4-octafluorocyclopentane, 1,1,2,2,3,4,4,5-octafluorocyclopentane, nonafluorocyclopentane and 1,1,2,2,3,3,4,4,5,6-decafluorocyclohexane are preferable. 1,1,2,2,3,4,5-Heptafluorocyclopentane, 1,1,2,3,3,4,5-heptafluorocyclopentane, 1,1,2,2,3,3,4,5-octafluorocyclopentane, 1,1,2,2,3,4,4,5-octafluorocyclopentane and 1,1,2,2,3,3,4,4-octafluorocyclopentane are especially preferable.
These cyclic hydrofluorocarbons may be used either alone or in combination.
The rinsing solvent used in the present invention is predominantly comprised of the above-mentioned cyclic hydrofluorocarbon. More specifically, the rinsing solvent can be composed of the cyclic hydrofluorocarbon alone (i.e., a single cyclic hydrofluorocarbon or a mixture of at least two cyclic hydrofluorocarbons), or a combination of the cyclic hydrofluorocarbon with other organic solvent. As specific examples of the other organic solvent, there can be mentioned those which are conventionally used as rinsing solvents, which include saturated straight-chain hydrocarbons such as hexane, octane and isooctane; saturated cyclic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as dimethyl ether and diethyl ether; esters such as vinyl acetate; straight-chain hydrofluorocarbons such as 1,1,1,2,2,3,4,5,5,5-decafluoropentane; and perfluorocarbons such as perfluorohexane and perfluoroheptane. These organic solvents may be used either alone or as a combination of at least two thereof. The amount of these organic solvents is suitably chosen in a range such that the effect of the invention can be achieved, and is usually not larger than 40% by weight, preferably not larger than 20% by weight and more preferably not larger than 10% by weight, based on the total weight of the rinsing solvents.
As the procedure of rinsing the article taken from the cleaning step (1), a conventional rinsing procedure can be adopted wherein the article is placed in contact with the cleaning solvent. More specifically procedures such as hand wiping, dipping, spraying and showering can be adopted. Of these, dipping is preferable. When a dipping procedure is employed, a physical means such as ultrasonic vibration, rocking, stirring and brushing may be additionally adopted. These rinsing procedures may be employed either alone or in combination. The temperature of the rinsing solvent is suitably chosen depending upon the particular nature of the article, but is usually in the range of from room temperature to the boiling point, preferably from 40°C to the boiling point and more preferably from 50°C to the boiling point.

(3) Step of Phase Separation into Two Layers

When the rinsing solvent used in the above-mentioned rinsing step (2) is repeatedly used, the hydrocarbon used as the cleaning solvent is concentrated with the result of reduction of the rinsing power. Therefore, the concentrated hydrocarbon must be removed. The removal of the hydrocarbon is effected by a procedure of phase separation into two layers in the process of the present invention.
The hydrocarbon used in the cleaning step (1) and the cyclic hydrofluorocarbon used in the rinsing step (2) are separated into an upper hydrocarbon layer and a lower cyclic hydrofluorocarbon layer due to the difference in specific gravity. The removal of the hydrocarbon can be effected by adding a fresh cyclic hydrofluorocarbon in the same vessel whereby the hydrocarbon is allowed to overflow from the vessel. But, preferably, a procedure is conducted wherein a part of the rinsing solvent used in the step (2) is transferred from the vessel into another vessel where it is phase-separated into an upper hydrocarbon layer and a lower cyclic hydrofluorocarbon layer; and the hydrofluorocarbon in the lower layer is recovered and returned to the initial vessel. The phase-separation into two layers can also be effected by centrifugal separation.
A hydrocarbon exhibits a high solubility at a high temperature in the cyclic hydrofluorocaron used in the present invention, but, the solubility is very low at a low temperature which is similar to the solubility of a hydrocarbon in a straight-chain hydrofluorocarbon or a perfluorocarbon. Therefore, the phase-separation into two layers is preferably conducted at a low temperature, i.e., usually at least 10°C lower, preferably at least 20°C lower and more preferably at least 30°C lower than the rinsing solvent temperature. The lower limit of the phase separation temperature is preferably the melting temperatures of the hydrocarbon and the cyclic hydrofluorocarbon or higher. The procedure by which the rinsing solvent is cooled is not particularly limited. For example, a procedure of allowing the rinsing solvent to stand at room temperature, a procedure of cooling the rinsing solvent by a cooling medium, or a procedure of vaporizing a part of the rinsing solvent to thereby cool the rinsing solvent by the heat of vaporization can be adopted. The rate of cooling also is not particularly limited, but a forced cooling such as a cooling from the outside or a vaporization under a reduced pressure is preferably in view of the high cooling efficiency and the minimization of loss of the rinsing liquid due to natural vaporization.
The cyclic hydrofluorocarbon recovered by the above-mentioned phase separation into two layers can be used, either as it is, or after it is subjected to a treatment such as distillation, filtration, activated carbon-treatment and drying, as the rinsing solvent for the rinsing step (2) or as a solvent for a vapor-washing step (4) mentioned below.

(4) Vapor Cleaning

The vapor cleaning can be carried out by a conventional procedure. The solvent used for the vapor cleaning is not particularly limited and those which are generally used for vapor cleaning can be used. In the process of the present invention, the cyclic hydrofluorocarbon recovered from the phase-separation step (3) has a high purity, and therefore, the thus-recovered cyclic hydrofluorocarbon can be used as a solvent for the vapor cleaning step (4), and thereafter, allowed to cycle for the use as a rinsing solvent in the rinsing step (2).
The present invention will now be described referring to Fig. 1 illustrating an example of a cleaning apparatus used in the process of the present invention.
An article having attached thereto oil, wax, flux or other dirty substances is dipped in a cleaning bath predominantly comprised of a hydrocarbon in a first cleaning vessel 1 where the dirty substances are removed from the surface of the article. The article placed in the cleaning bath in the first cleaning vessel can be subjected to an ultrasonic cleaning by an ultrasonic vibrating apparatus 10 and/or can be heated by a heater 9 to enhance the cleaning power.
When the cleaning effect obtained in the first cleaning vessel 1 is not sufficient, a second cleaning vessel 2 can be additionally used. In the second cleaning vessel 2, if desired, a heater 9 and/or an ultrasonic vibrating apparatus 10 can be used in a manner similar to in the first cleaning vessel. In the example illustrated in Fig. 1, two cleaning vessels are used, but, the number of cleaning vessels is not particularly limited, and one or more of cleaning vessels can be used.
The article having attached thereto the cleaning solvent (hydrocarbon) taken from the cleaning vessel is then dipped in a rinsing bath predominantly comprised of a cyclic hydrofluorocarbon in a rinsing vessel 3. To enhance the rinsing power, an ultrasonic cleaning using an ultrasonic vibrating apparatus 10, a showering cleaning and/or a rocking cleaning may be additionally employed. In the rinsing vessel 3, the hydrocarbon attached onto the surface of the article is separated from the article surface. The separated hydrocarbon is transferred to a separation vessel 4 by a rinsing liquid-transferring pump 14, by allowing the hydrocarbon to overflow, or by a stream of an additional rinsing solvent accompanied by the hydrocarbon.
The hydrocarbon exhibits an enhanced solubility in the cyclic hydrofluorocarbon constituting the major ingredient of the rinsing solvent, and therefore, to enhance the rinsing effect, the rinsing solvent bath is preferably heated by a heater 9. By supplying a fresh cyclic hydrofluorocarbon by a cycling pump 11 or 12, the rinsing solvent bath in the rinsing vessel 3 can be maintained at a uniform state without formation of an upper hydrocarbon layer. Therefore, the problem encountered in the prior art that, when the rinsed article is taken out from the rinsing bath, the hydrocarbon is again attached from the upper layer to the article, can be solved. The uniform rinsing solvent used is transferred to the phase separation vessel 4 in a manner similar to that mentioned above.
In a separating vessel 4, the rinsing solvent from the rinsing vessel 3 is separated into an upper hydrocarbon layer 6 and a lower hydrofluorocarbon layer 7 due to the difference in specific gravity. When the hydrofluorocarbon in the lower layer is a cyclic compound, both solubility of the cyclic hydrofluorocarbon in the hydrocarbon and solubility of the hydrocarbon in the cyclic hydrofluorocarbon greatly vary depending upon the variance of temperature, and both the solubilities are very low in a low temperature region. Therefore, by lowering the temperature of the separation vessel 4, a cyclic hydrofluorocarbon having a high purity can be recovered and the incorporation of a cyclic hydrofluorocarbon in the upper hydrocarbon layer can be minimized. Thus, the operation of the phase-separation into the two layers is conducted usually at least 10°C lower, preferably at least 20°C lower and more preferably at least 30°C lower than the temperature of the rinsing bath in the rinsing vessel 3.
The cyclic hydrofluorocarbon in the lower layer 7 is cycled to the rinsing vessel 3 by a cycling pump 11 and to a vapor cleaning vessel 5 by a cycling pump 12.
The vapor cleaning is carried out when a high degree of cleaning is required or the amount of the cyclic hydrofluorocarbon used is reduced. In this case, the cyclic hydrofluorocarbon recovered is transferred by the cycling pump 12 to the vapor cleaning vessel 5 where it is heated by a heater 9 to form a vapor zone 8. The article taken from the rinsing vessel 3 is subjected to a vapor cleaning in the vapor zone 8 composed of the cyclic hydrofluorocarbon. The cyclic hydrofluorocarbon used for the vapor cleaning is cycled to the rinsing vessel 3 by an overflow or cohesion where the cyclic hydrofluorocarbon is reused.
Figure 1 is a diagrammatic sectional view illustrating an example of a cleaning apparatus used in the cleaning process of the present invention. The particulars of the cleaning procedure, the rinsing procedure, the phase-separation procedure and the vapor cleaning procedure are not particularly limited to those which are mentioned above. Other general procedures may be employed, and the number of times for cleaning and rinsing can be varied.
The invention will now be specifically described by the following examples that by no means limit the scope of the invention.

Examples 1 to 5

The cleaning apparatus illustrated in Fig. 1 was used. Two cleaning vessels (first cleaning vessel 1 and second cleaning vessel 2), each equipped with a heater 9 and an ultrasonic vibrating apparatus 10, were charged with a cleaning solvent composed of a hydrocarbon having 13 carbon atoms ("NS Clean" supplied by Nikkou Petrochemical Co.). A rinsing vessel 3 equipped with a heater 9 and an ultrasonic vibrating apparatus 10 was charged with 1,1,2,2,3,3,4,5-octafluorocyclopentane (OFCPA). The cyclic hydrofluorocarbon recovered in a separating vessel 4 was transferred to a vapor cleaning apparatus (vapor cleaning vessel 5) equipped with a cooling tube 13, and vaporized therein to form a vapor zone 8. The temperature of the separating vessel 4 was controlled to 20°C.
Each smearing substance shown in Table 1 was dissolved in 1,1,1-trichloroethane at a concentration of 25% by weight, and 0.1% by weight of a Sudan dye as a tracer was incorporated therein. Each article shown in Table 1 was dipped in the thus-prepared smearing substance solution to prepare a smeared article. The amount of the smearing substance attached to the article was determined by measuring the weight of the article before and after the dipping, and calculating the weight difference.
A cleaning test of the smeared article was carried out while the smeared article was transferred successively to a first cleaning vessel 1, a second cleaning vessel 2, a rinsing vessel 3, and then, a vapor cleaning vessel 5, and the following procedures were conducted.
(1) First cleaning vessel 1: the smeared article was dipped in the first cleaning bath at 50°C and an ultrasonic vibration was conducted for 3 minutes.
(2) Second cleaning vessel 2: the smeared article from the vessel (1) was dipped in the second cleaning bath at 50°C and an ultrasonic vibration was conducted for 1 minute.
(3) Rinsing vessel 3: the article from the vessel (2) was dipped in the rinsing bath at 50°C and an ultrasonic vibration was conducted for 1 minute.
(4) Vapor cleaning vessel: the article from the vessel (3) was placed in a vapor zone 8 formed with the recovered 1,1,2,2,3,3,4,5-octafluorocyclopentane (OFCPA) (boiling point: 80°C) in the vapor cleaning vessel 8 for 2 minutes.
Cleaning characteristics were evaluated on the thus-cleaned article according to the following methods, and the results are shown in Table 1.

(1) Amount of Residual Smearing Substance

Each cleaned article was treated with a predetermined amount of 1,1,1-trichloroethane whereby both residual smearing substance and dye were extracted. Absorbance of red color of Sudan dye was measured at a wavelength of 550 nm, and the residual amount of the smearing substance was calculated from a calibration curve.

(2) Visual Evaluation

The appearance of each cleaned article was visually observed and evaluated according to the following three ratings.

A:: No smears were observed.
B:: Slight smears were observed.
C:: Clear smears were observed.

(3) Evaluation of Odor

Each cleaned article was smelled and the odor was evaluated according to the following three ratings.

A:: No oily smell was perceived.
B:: Slight oily smell was perceived.
C:: Clear oily smell was perceived.

Comparative Example 1

Cleaning test was conducted by the same procedures as those described in Example 1 except that the rinsing solvent used was substituted by 1,1,1,2,2,3,4,5,5,5-decafluoropentane (i.e., a straight-chain hydrofluorocarbon) (DFPA; boiling point: 55°C) with all other conditions remaining the same. The results are shown in Table 2.

Comparative Example 2

Cleaning test was conducted by the same procedures as those described in Example 1 except that the rinsing solvent used was substituted by perfluorohexane (i.e., a perfluorocarbon) (PFHX; boiling point: 56°C) with all other conditions remaining the same. The results are shown in Table 2.

Example No.	Articles	Smearing substance	Residue amount (%)	Visual evaluation	Odor
1	Bolt, nut	Cutting oil	0.0	A	A
2	Epoxy resin coated glass	Flux	0.02	A	A
3	Glass bottle	Silicone oil	0.01	A	A
4	Blade of printing machine	Oil soluble ink	0.05	A	A
5	Optical glass lens	Fats and oils	0.0	A	A

Comp. Exam. No.	Fluorinated solvent	Residue amount (%)	Visual evaluation	Odor
1	1,1,1,2,2,,3,4,5,5,5-Decafluoropentane	0.25	B	C
2	Perfluorohexane	0.5	B	C

As seen from Tables 1 and 2, in the examples of the invention (Examples 1 to 5), good results are obtained for all of the evaluation of amount of residual smearing substance, the visual evaluation and the evaluation of odor. In contrast, in the case where a straight-chain hydrofluorocarbon is used as a rinsing solvent (Comparative Example 1), the results of the evaluation of amount of residual smearing substance and the evaluation of odor are not satisfactory, and thus, the rinsing effect is poor. In the case where a perfluorocarbon is used as a rinsing solvent (Comparative Example 2), the results of the evaluation of amount of residual smearing substance and the evaluation of odor also are not satisfactory, and thus, the rinsing effect is poor.

Example 6, Comparative Example 3

The cleaning procedures employed in Example 1 and Comparative Example 1 were repeated 20 times, and the cleaning effects were evaluated. The results are shown in Table 3.

No.	fluorinated solvent	Residue amount (%)	Visual evaluation	Odor	State of solution
Example 6	1,1,2,2,3,3,4,5-Octafluorocyclopentane	0.01	A	A	Uniform
Comp. Ex.3	1,1,1,2,2,3,4,5,5,5-Decafluoropentane	0.5	C	C	Phase separation
Note: State of Solution was expressed by the fact whether the recovered rinsing solvent was "uniform" or "separated into an upper hydrocarbon layer and a lower rinsing solvent layer".

As seen from Table 3, in the present invention, even when a rinsing solvent is repeatedly used, a high rinsing effect can be obtained (Example 6). In contrast, when a straight-chain hydrofluorocarbon is used as a rinsing solvent, the rinsing effect is drastically reduced (Comparative Example 3). This would be because the rinsing solvent is kept in a uniform state in Example 6, whereas, an upper hydrocarbon layer is formed and, when the article is taken out from the rinsing bath, the hydrocarbon is again attached to the article in Comparative Example 3.

Reference Examples 1 to 7 (Recovery of Cyclic Hydrofluorocarbon in Separating Vessel 4)

A mixture of 10 g of each hydrocarbon shown in Table 4 and 100 ml of each cyclichydrofluorocarbon was prepared (Reference Example 1 to 7). A 200 ml flask provided with a magnet stirrer was charged with the mixture, and the content was gradually heated to 75°C while being stirred to prepare a uniform solution.
Thereafter, the uniform solution was transferred to a separating vessel 4 (Fig. 1) maintained at 20°C where the solution became turbid and then separated into two layers. A gas chromatographic analysis of the lower layer revealed that all of the hydrofluorocarbon layers were of a high purity, and thus, substantially the entire amount of the hydrofluorocarbon used was recovered.

Reference Examples 8 to 10

The procedures employed in Reference Example 1 were repeated wherein a mixture of 50 g of each hydrocarbon shown in Table 4 and 50 g of 1,1,2,2,3,3,4,5-octafluorocyclopentane was used as the hydrocarbon/hydrofluorocarbon mixture with all other conditions remaining the same (Reference Examples 8 to 10). It was proved that these combinations of a hydrocarbon with octafluorocyclopentane formed a uniform solution at any proportion at 75°C, but, were separated into two layers at 20°C and recovered with a purity shown in Table 4.

Ref. Ex. No.	Hydrocarbon	Alicyclic hydrofluorocarbon	Purity (%)
1	n-tridecane	OFCP	>98
2	n-tridecane	HXFCP	>98
3	n-tridecane	HPFCP	>98
4	n-tridecane	mixture of OFCP and HPFCP (ratio = 90:10 by weight)	>98
5	n-decane	OFCP	>97
6	n-dodecane	OFCP	>98
7	decalin	OFCP	>97
8	1-decene	OFCP	>92
9	limonene	OFCP	>80
10	α-pinene	OFCP	>90

Reference Example 11 (Solubility Characteristics of Cyclic Hydrofluorocarbon)

A 10 ml vial was charged with 5 ml of 1,1,2,2,3,3,4,5-octafluorocyclopentane (OFCPA) and 5 ml of NS Clean 230 and then covered up with a cap. The vial was shaken thoroughly to stir the content, and maintained at the temperature shown in Table 5 for 2 hours. The solubility of the respective ingredients was measured by a gas chromatography. The results are shown in Table 5.

Reference Example 12 (Solubility Characteristics of Straight-chain Hydrofluorocarbon)

The procedures employed in Reference Example 11 were repeated wherein 1,1,1,2,2,3,4,5,5,5-decafluoropentane (DFPA) was used instead of 1,1,2,2,3,3,4,5-octafluorocyclopentane (OFCPA) with all other conditions remaining the same. The solubility of the respective ingredients was measured and the results are shown in Table 6.

Reference Example 13 (Solubility Characteristics of Perfluorocarbon)

The procedures employed in Reference Example 11 were repeated wherein perfluoro-n-heptane (PFHP) was used instead of 1,1,2,2,3,3,4,5-octafluorocyclopentane (OFCPA) with all other conditions remaining the same. The solubility of the respective ingredients was measured and the results are shown in Table 7.

Temp. (°C) Amount of NS Clean 230 dissolved (g/mL OFCPA) Amount of OFCPA disolved (g/mL NS Clean 230)

0 - 0.003

20 0.018 0.010

40 0.063 0.025

55 0.092 0.039

75 0.123 0.063

Temp. (°C) Amount of NS Clean 230 dissolved (g/mL DFPA) Amount of DFPA dissolved (g/mL NS Clean 230)

0 0.008 0.031

20 0.017 0.048

40 0.033 0.104

55 0.046 0.133

Temp. (°C) Amount of NS Clean 230 dissolved (g/mL PFHP) Amount of PFHP dissolved (g/mL NS Clean 230)

0 0.009 0.012

20 0.011 0.022

40 0.023 0.032

55 0.030 0.058
The following will be seen from Tables 5, 6 and 7.
(1) Solubility of a hydrofluorocarbon in a cyclic hydrofluorocarbon is high at a high temperature, as compared with the solubilities in a straight-chain hydrofluorocarbon and in a perfluorocarbon. But, at a low temperature, the solubility in a cyclic hydrofluorocarbon is low and approximately the same as those in a straight-chain hydrofluorocarbon and in a perfluorocarbon. Further, the incorporation of a cyclic hydrofluorocarbon in a hydrofluorocarbon layer recovered at a low temperature is extremely low. Therefore, a cyclic hydrofluorocarbon is suitable as a rinsing solvent used in the cleaning process of the present invention.
(2) Solubility of a hydrocarbon in a straight-chain hydrofluorocarbon is not so high even at a high temperature, and thus, the rinsing power of a straight-chain hydrofluorocarbon is poor. Further, the expensive straight-chain hydrofluorocarbon is incorporated in a salient amount into an upper hydrocarbon layer formed by phase-separation at 20°C, and thus, the use of straight-chain hydrofluorocarbon rinsing solvent is not advantageous from an economical view point.
(3) Solubility of a hydrocarbon in a perfluorocarbon is poor.

Industrial Applicability

According to the present invention, a co-solvent system wherein a smeared article is cleaned with a hydrocarbon solvent, followed by using a fluorine-containing solvent for rinsing, vapor cleaning and drying, is advantageously employed.
Further, a perfect cyclic cleaning system can be employed by providing a separation apparatus for phase-separating into two layers at a low temperature, and conducting a recovery of a cyclic hydrofluorocarbon and introducing the recovered cyclic hydrofluorocarbon into a rinsing vessel according to the present invention. Thus, the cleaning can be achieved at a reduced running cost.
The cleaning process of the present invention is suitable for cleaning various smeared articles, which include, for example, those made of metals, ceramics, glass, plastics, elastomers and other materials and used in a precision machine industry, a metal machining industry, an optical machine industry, a plastic industry and other industries. As specific examples of the articles, there can be mentioned automobile parts such as bumpers, transmission gears, transmission parts and radiator parts, electronic and electrical parts such as printed circuit boards, IC parts, lead frames, motor parts and capacitors, precision machine parts such as bearings, gears, engineering plastic toothed gears, clock and watch parts, camera parts and optical lenses, large-size machine parts such as printing machines, blades for a printing machine, printing rolls, rolled articles, construction machines, glass substrates and large-size heavy machine parts, and daily necessities such as tableware.
The substances causing smears on the articles include, for example, oils such as cutting oil, quenching oil, rolling oil, lubricating oil, machining oil, press-machining oil, punching oil, drawing oil, assembling oil and inking oil, greases, waxes, adhesives, fats and oils, mold releasing agents, dirt from the hands, soldering fluxes, resists and solder pastes.

Claims

A process for cleaning an article comprising the steps of:

(1) a cleaning step of placing an article in contact with a cleaning solvent predominantly comprised of a hydrocarbon,

(2) a rinsing step of placing the article taken from the cleaning step (1) and having attached thereto the cleaning solvent, in contact with a rinsing solvent predominantly comprised of a hydrofluorocarbon, and

(3) a separation step of separating into two layers the hydrocarbon-containing rinsing solvent discharged from the rinsing step (2) by a phase separation,
characterized in that the hydrofluorocarbon used is a cyclic compound, in which the number of fluorine atoms is larger than the number of hydrogen atoms.
The cleaning process according to claim 1, wherein the hydrofluorocarbon has 4 to 10 carbon atoms and 1 to 5 hydrogen atoms.
The cleaning process according to claim 1 or claim 2, wherein the process further comprises, subsequently to the rinsing step (2):

(4) a vapor cleaning step of cleaning with vapor the article taken from the rinsing step (2).
The cleaning process according to any of claims 1 to 3, wherein the separation step (3) comprises taking the hydrocarbon-containing rinsing solvent from the rinsing step (2), and separating the rinsing solvent into a hydrocarbon layer and a hydrofluorocarbon layer.
The cleaning process according to claim 4, wherein the hydrofluorocarbon layer separated in the separation step (3) is recovered and used as at least part of the rinsing solvent supplied to the rinsing step (2).
The cleaning process according to claim 4, wherein the hydrofluorocarbon layer separated in the separation step (3) is recovered and used as at least part of the solvent for vapor cleaning supplied to the vapor cleaning step (4).
The cleaning process according to claim 4, wherein the hydrofluorocarbon layer separated in the separation step (3) is recovered and used as at least part of the solvent for vapor cleaning supplied to the vapor cleaning step (4), and further recovered, after the use in the vapor cleaning step, and used as at least part of the rinsing solvent supplied to the rinsing step (2).
The cleaning process according to any of claims 1 to 7, wherein the separation step (3) of separating the hydrocarbon-containing rinsing solvent into two layers is conducted at a temperature at least 10°C lower than that of the rinsing solvent in the rinsing step (2).