JP2013116959A - Method of removing polyvinyl alcohol from cultural properties - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method of removing a polyvinyl alcohol (PVA) film applied to a surface of cultural properties such as paintings as a peel-off stopper.SOLUTION: A method of removing polyvinyl alcohol from cultural properties includes bringing the cultural property subjected to restoration with the polyvinyl alcohol into contact with an enzyme composition, wherein the enzyme composition comprises: an enzyme that can oxidize the polyvinyl alcohol; and an enzyme that can hydrolyze the polyvinyl alcohol thus oxidized.

Description

  The present invention relates to a method for removing polyvinyl alcohol from a cultural property and a method for restoring the cultural property.

  Polyvinyl alcohol (PVA) is a synthetic resin that is capable of forming a few water-soluble and transparent films. For this reason, PVA is widely used industrially as a raw material for vinylon fibers, fiber pastes, paper processing agents, adhesives, films, polymerization aids, and the like.

  There are many precious paintings in Japan, which are designated as important cultural properties and kept strictly. However, since these cultural assets have been produced for hundreds to over a thousand years, depending on the type of materials, the environment in which they were placed, and the techniques used, depending on the work There are various effects. For example, some paintings have undergone considerable degradation and partial peeling. As described above, since PVA is water-soluble, it can be used by dissolving in water, and a transparent film can be formed. For this reason, PVA has been used as a restoration material that prevents the peeling of paintings and protects the surface of paintings and the like since the 1950s (Non-Patent Document 1).

  However, several decades after the restoration process, it has been reported that problems such as re-peeling the pigment layer and whitening of the surface have caused problems such as the inability to appreciate the original colors of paintings, etc. It has been reported that this is due to deterioration of PVA used as a flaking stopper (Non-patent Document 1). In other words, depending on the environment in which the cultural property is placed, for example, the influence of air, light, moisture, etc., the PVA may be hardened / shrinked, the pigment may be involved and peeled, or the PVA may be whitened. For this reason, attempts have been made to remove PVA from cultural properties.

Kiyoji Higuchi, retrospective: The beginning of the use of synthetic resin for cultural property repair in Japan (National Ethnographic Museum Survey Report 36 “Synthetic Materials and Museum Materials”), 53-91 (2003)

  However, although PVA is water-soluble, it is practically difficult to re-dissolve in water at room temperature. In many cases, heating and soaking for a long time are required to re-dissolve in water. In particular, aged PVA no longer dissolves in water and is not easy to swell. Moreover, it cannot be removed even if it is chemically treated with an organic solvent or the like, and further, if it is physically removed, the painting is likely to be damaged. For this reason, it was thought that removal of PVA used for the painting surface was very difficult.

  Therefore, the present invention provides a new method capable of removing the PVA film applied as a flaking stop on the surface of a cultural property such as a painting.

  In one aspect, the present invention provides a cultural property that has been repaired with polyvinyl alcohol, an enzyme that can oxidize polyvinyl alcohol, and an enzyme composition that includes an enzyme that can hydrolyze the oxidized polyvinyl alcohol. The present invention relates to a method for removing polyvinyl alcohol from a cultural property, including contact.

  In another aspect, the present invention relates to a method for restoring a cultural property, including removing polyvinyl alcohol from the cultural property by the method for removing polyvinyl alcohol of the present invention.

  According to the present invention, polyvinyl alcohol can be easily removed from a cultural property that has been restored using polyvinyl alcohol without damaging the cultural property.

FIG. 1 shows a digital microscope photograph of a PVA film. FIG. 2 shows a photograph showing an example of a result of treatment with an enzyme solution using a deteriorated PVA film formed on a gold foil surface as a sample. FIG. 3 shows a photograph showing an example of the result of processing with an enzyme solution using a fallen cultural property as a sample.

  The present invention can easily remove a deteriorated PVA film formed on the surface of a cultural property by using an enzyme composition containing an enzyme capable of oxidizing polyvinyl alcohol and an enzyme capable of hydrolyzing oxidized polyvinyl alcohol. Based on the knowledge that

  The details of the mechanism by which the degraded PVA membrane can be easily removed by using the enzyme composition are not clear, but are estimated as follows. First, an enzyme composition containing an enzyme capable of oxidizing polyvinyl alcohol and an enzyme capable of hydrolyzing oxidized polyvinyl alcohol acts on the PVA film on the surface of the cultural property, whereby the PVA molecules are cleaved and PVA is removed. Low molecular weight. As a result, since the adhesive force between the PVA film and the cultural property becomes weak, it is estimated that PVA can be easily removed from the cultural property. However, the present invention need not be limited to these mechanisms.

  According to the PVA removal method of the present invention, PVA can be easily removed from the cultural property without damaging the cultural property, and even PVA that has deteriorated and / or whitened can be easily removed. Can have an effect. According to the PVA removal method of the present invention, for example, PVA can be easily removed (peeled) even by treatment with an enzyme composition in a short time (for example, less than 1 hour). The effect on this can be greatly reduced. By removing PVA, it is possible to prevent occurrence of peeling and whitening of the surface of the cultural property due to PVA in the cultural property to be preserved in the future. In many cases, the cultural property is re-restored. However, according to the PVA removal method of the present invention, the PVA that has been difficult to remove can be easily removed, so that the cultural property can be easily re-restored. .

[Enzyme composition]
In the present specification, the “enzyme composition” includes an enzyme capable of oxidizing polyvinyl alcohol and an enzyme capable of hydrolyzing the oxidized polyvinyl alcohol. The enzyme capable of oxidizing polyvinyl alcohol preferably contains secondary alcohol oxidase (EC 1.1.3.18). The enzyme capable of hydrolyzing oxidized polyvinyl alcohol preferably comprises β-diketone hydrolase (EC 3.7.1.7). As an enzyme composition, the enzyme composition obtained by culture | cultivating the culture solution or culture | cultivation of the bacteria which have a polyvinyl alcohol degrading enzyme production ability, or culture | cultivation, for example may be included. Examples of bacteria having the ability to produce polyvinyl alcohol-degrading enzymes include Pseudomonas bacteria, Acinetobacter bacteria, and Sphingomonas bacteria. The culture solution and enzyme composition are described in, for example, Agric. Biol. Chem., 43 (6), 1225-1235, 1979, Agric. Biol. Chem., 49 (3), 827-833, 1985, Agric. Biol. Chem., 49 (6), 1901 -1902, 1985, Agric. Biol. Chem., 50 (4), 989-996, 1986, etc.

[Cultural property]
In this specification, “cultural property” indicates a tangible cultural property. Tangible cultural property means buildings, paintings, sculptures, crafts, handwriting, classics, ancient documents, other tangible cultural products, archeological materials, and historical materials. In this specification, important cultural properties, etc. Can include designated cultural properties. Although it does not specifically limit as a cultural property, For example, a picture, a building coloring, etc. are mentioned. Paintings can include barrier paintings, shafts, and the like. Examples of the barrier painting may include a building mural, Sugito painting, folding screen, screen and screen. In this specification, “a cultural property that has been repaired by PVA” refers to a cultural property to which a PVA solution has been applied, such as protection and / or strengthening of the surface of the cultural property, peeling and peeling or powdering, cracking, and the like. It is a cultural property that is coated with water-soluble PVA for the purpose of restoration and / or prevention.

[Polyvinyl alcohol]
As used herein, “polyvinyl alcohol (PVA)” may include a part that has deteriorated over time, a part that is insoluble in water, and / or a part that has been whitened. That is, as used herein, PVA is all aged, water-insoluble and / or whitened PVA, aged, partially water-insoluble and / or partially whitened, and aged. PVA may be included that is water insoluble and / or free of whitened portions. In this specification, “aging-degraded PVA” refers to, for example, PVA that has been applied to a cultural property over 2 years, 5 years, 10 years, or 15 years, preferably immediately after formation. This refers to a PVA film that can partially or completely include interchain dehydration, intrachain dehydration, and chemical cross-linking (C—O ether bond), which are not found in PVA films (Polymer Journal (2011) 43, 74). −77). These can be confirmed by, for example, FT-IR and XPS measurement (Polymer Journal (2011) 43, 74-77).

  General PVA is said to be completely dissolved if it is stirred in water at 80 to 95 ° C. for 30 to 60 minutes. “PVA is insoluble in water” can include, for example, that PVA does not completely dissolve when PVA is immersed in water at room temperature for about 1 day. In the case of a PVA film formed on a cultural property or a base material, “PVA is insoluble in water” means, for example, that it is immersed in water for several hours at room temperature without stirring or shaking. The strength of PVA cannot be reduced to such an extent that PVA can be removed even if it is allowed to stand still, preferably to the extent that PVA can be removed without damaging the cultural assets, pigments of the base material, paper, silk, etc. To the extent that the strength of the PVA is not reduced. Examples of the strength of PVA include elasticity and viscosity of a PVA film. In the present specification, “whitened PVA” refers to PVA that has turned white, and may include, for example, PVA that has become cloudy due to cracks or micrometer-sized wrinkles generated on the PVA surface. Cracks and wrinkles on the PVA surface can be confirmed by, for example, SEM.

  In the PVA in the present specification, the polymerization degree and saponification degree of the PVA used as a raw material are not particularly limited, but in general, the polymerization degree is 400 to 3900, and the saponification degree is 70 to 99 mol%. And the like.

[Method of removing PVA from cultural assets]
In one aspect, the present invention provides a cultural property that has been repaired with polyvinyl alcohol, an enzyme that can oxidize polyvinyl alcohol, and an enzyme composition that includes an enzyme that can hydrolyze the oxidized polyvinyl alcohol. The present invention relates to a method for removing polyvinyl alcohol from a cultural property, including contact (hereinafter also referred to as “PVA removal method of the present invention”).

  In this specification, “removing PVA” includes, for example, peeling the PVA film on the surface of the cultural property, dissolving the PVA, separating the PVA from the cultural property, and the like. From the viewpoint of removing PVA while further reducing the influence on cultural properties, it is preferable to remove PVA by peeling the PVA film. Therefore, the PVA removal method of the present invention may include, for example, peeling a film-like PVA formed on the surface of the cultural property from the cultural property.

  It is preferable that the enzyme composition brought into contact with the cultural property is liquid. The pH of the enzyme composition at the time of contact is, for example, 5 to 9, and 6 to 8 is preferable from the viewpoint of removing PVA while further reducing the influence (damage) on the cultural property. Although the temperature of the enzyme composition at the time of contact is not specifically limited, For example, it is 0-40 degreeC, From the point which removes PVA, without changing the environment to which a cultural property is exposed significantly, it is 10 ~ 20 ° C is preferred. In the enzyme composition, the polyvinyl alcohol oxidation activity is, for example, 1 to 200 mU / ml, and 20 to 40 mU / ml is preferable from the viewpoint of removing PVA while further reducing the influence (damage) on the cultural property. The polyvinyl alcohol decomposition activity is, for example, 10 to 5000 mU / ml, and 500 to 1000 mU / ml is preferable from the viewpoint of removing PVA while further reducing the influence (damage) on the cultural property. From the point of removing PVA while reducing the influence (damage) on cultural assets as much as possible, the treatment with the enzyme composition is performed with the smallest amount of enzyme (protein concentration) and the shortest treatment time possible. It is preferable to carry out with. For this reason, the enzyme amount (protein concentration) in the enzyme composition is, for example, 2 to 400 μg / ml, and 20 to 100 μg / ml from the viewpoint of removing PVA while further reducing the influence (damage) on the cultural property. Is preferred. Polyvinyl alcohol oxidation activity and polyvinyl alcohol decomposition activity are defined as described in the examples, and can be calculated as described in the examples.

  The contact between the cultural property and the enzyme composition can be performed by applying, dropping, spraying, etc. the enzyme composition to the cultural property, for example. The contact between the cultural property and the enzyme composition may be performed by covering the cultural property with a sheet containing the enzyme composition and leaving it in that state for a predetermined time.

  The time for contacting with the enzyme composition is not particularly limited and can be appropriately determined according to the contacting method. For example, it is 1 to 240 minutes, and more efficiently while reducing the influence on the cultural property. 10-60 minutes is preferable from the point which removes PVA from a cultural property. Although the atmospheric temperature at the time of contact is not specifically limited, For example, it is 5-50 degreeC, and 15-35 degreeC from the point which removes PVA, without changing the environment to which a cultural property is exposed significantly. Is preferred.

  It is preferable to include washing the cultural property with which the enzyme composition is contacted. Thereby, PVA can be more efficiently removed from the cultural property while reducing the influence on the cultural property.

  The contact with the enzyme composition may be performed once or may be performed two or more times. When the contact with the enzyme composition is performed a plurality of times, the contact with the enzyme composition and the washing with water are preferably performed alternately.

  According to the PVA removal method of the present invention, PVA that can adversely affect a cultural property can be removed in a state in which the influence on the cultural property is sufficiently reduced, so that the restoration, protection, and / or conservation of the cultural property is performed. Useful for. For this reason, this invention can provide the restoration, protection, or preservation method of a cultural property including the removal process of PVA by the PVA removal method of this invention as another aspect.

[How to restore cultural properties]
The restoration method of the present invention includes removing polyvinyl alcohol from a cultural property by the PVA removal method of the present invention. According to the repairing method of the present invention, PVA can be efficiently removed from the cultural property, and therefore, the restoration of the cultural property restored with PVA can be performed more efficiently. In addition, the restoration was performed without removing PVA in the past, but according to the restoration method of the present invention, PVA can be easily removed, greatly reducing the impact on cultural properties. However, better repair is possible.

[PVA decomposition method]
In still another aspect, the present invention provides polyvinyl alcohol (hereinafter also referred to as “PVA to be treated”) including at least one part selected from the group consisting of a part that has deteriorated over time, a part that is insoluble in water, and a part that has been whitened. Is contacted with an enzyme composition comprising an enzyme capable of oxidizing polyvinyl alcohol and an enzyme capable of hydrolyzing the oxidized polyvinyl alcohol.

  The contact with the enzyme composition can be performed by applying the enzyme composition to the PVA to be treated, for example, by applying, dropping, spraying, etc., and immersing the PVA to be treated in the enzyme composition. May be performed. The contact condition with the enzyme composition can be carried out in the same manner as in the removal method of the present invention.

[Reagent for restoration of cultural assets]
In yet another aspect, the present invention provides a reagent for repairing cultural properties comprising an enzyme capable of oxidizing polyvinyl alcohol and an enzyme capable of hydrolyzing oxidized polyvinyl alcohol (hereinafter referred to as “the reagent of the present invention”). Also called). According to the reagent of the present invention, for example, the PVA removal method and the cultural property repair method of the present invention can be easily performed. The enzyme which can oxidize polyvinyl alcohol and the enzyme which can hydrolyze the oxidized polyvinyl alcohol can use the thing similar to the PVA removal method of this invention.

  The reagent may be in a dry powder state or in a liquid state dissolved in water or the like.

  The present invention will be further described below with reference to examples. However, the present invention is not construed as being limited to the following examples.

[Enzyme activity]
In this specification, unless otherwise specified, the enzyme activity of an enzyme solution is defined as follows.
[Polyvinyl alcohol oxidation activity]
An enzyme solution was allowed to act on polyvinyl alcohol as a substrate under the conditions of 30 ° C. and pH 7.0, and the amount of enzyme that produced 1 μmol of hydrogen peroxide per minute was defined as 1 unit (1 U).
[Polyvinyl alcohol decomposition activity]
An enzyme solution was allowed to act on polyvinyl alcohol as a substrate under the conditions of 30 ° C. and pH 7.0 to reduce the relative viscosity by 10% for 60 minutes to 1 unit (1 U).

The enzyme activity was measured as follows.
[Polyvinyl alcohol oxidation activity]
2.0 ml of a reaction solution containing 50 mM phosphate buffer (pH 7.0), 1.0% PVA, and an enzyme-containing sample to be measured was incubated at 30 ° C. for 30 minutes with stirring. In order to measure the generated hydrogen peroxide, 5.0 ml of a titanium reagent was added to the reaction solution, and the absorbance was measured at 410 nm.
[Polyvinyl alcohol decomposition activity]
20 ml of a reaction solution containing 50 mM phosphate buffer (pH 7.0), 1.0% PVA, and the enzyme-containing sample to be measured was incubated at 30 ° C. with stirring for 1 hour. The viscosity of the reaction solution was measured at 30 ° C. using an Ostwald viscometer. The decomposition activity was expressed as a relative viscosity reduction rate and was calculated based on the following formula.
Relative viscosity reduction rate (%) = {(Vo−Vt) / (Vo−Vw)} × 100
Vo: Viscosity of reaction liquid at zero reaction time Vt: Viscosity of reaction liquid at reaction t time Vw: Viscosity of water

(Example 1) Change in molecular weight due to enzymatic degradation of degraded polyvinyl alcohol [Preparation of degraded polyvinyl alcohol]
Two types of polyvinyl alcohols A and B (all manufactured by Wako Pure Chemical Industries, Ltd.) shown in Table 1 below were prepared. A PVA aqueous solution was prepared using polyvinyl alcohol A and B, respectively, and a PVA film having a thickness of 20 to 50 μm was prepared by casting and drying the PVA aqueous solution. The obtained PVA film was irradiated with an ozone lamp (GL-20Z, 253.7 nm, 185 nm) for 8 hours and then exposed to water vapor for 2 hours to prepare a deteriorated PVA film. In addition, it has already been confirmed that, by performing the above treatment, a whitened deteriorated PVA film can be formed in the same manner as an aged deteriorated PVA formed on cultural properties (Polymer Journal (2011) 43, 74-77). .

  The obtained PVA film (deteriorated PVA film) was whitened. FT-IR and XPS measurement of the deteriorated PVA film revealed that inter-chain and intra-chain dehydration and chemical cross-linking (C-O ether bond), which are not found in the PVA film before the deterioration treatment, were observed on the surface of the deteriorated PVA film. Has occurred.

[Preparation of enzyme solution]
A culture solution of the genus Pseudomonas cultured according to Arch. Biochem. Biophys., 174, 575 (1976) was salted out with ammonium sulfate and dialyzed with 50 mM potassium phosphate buffer (pH 7.0) with distilled water. The enzyme solution was prepared by diluting about 100 times. The enzyme activity of the obtained enzyme solution was about 30 mU / ml for polyvinyl alcohol oxidation activity and about 1 U / ml for polyvinyl alcohol decomposition activity. The enzyme solution contained secondary alcohol oxidase and β-diketone hydrolase. The protein concentration of the enzyme solution was about 30 μg / ml.

[Treatment of degraded PVA film with enzyme solution]
A few drops of the enzyme solution were dropped on the surface of the deteriorated PVA film prepared as described above, left at room temperature for about 5 minutes, and then air-dried. After air drying, it was dissolved in 0.1 M sodium nitrate as a solvent for gel permeation chromatography (GPC) measurement, filtered through a 0.45 μm microfilter, and then subjected to GPC analysis (column: TSKgel GMPWxL, apparatus: Tosoh GPC8220). The weight average molecular weight was determined. The results are shown in Table 2 below. Sample A in Table 2 shows the result of a deteriorated PVA film prepared using polyvinyl alcohol A, and Sample B shows the result of a deteriorated PVA film prepared using polyvinyl alcohol B. As shown in Table 2, the weight average molecular weight of each sample was greatly reduced by the treatment with the enzyme solution. Thus, since the molecular weight was significantly reduced, it was confirmed that the PVA film that was subjected to the deterioration treatment and became water-insoluble could be decomposed by performing the treatment using the enzyme solution. Further, the degraded PVA film could be decomposed by the enzyme solution without being related to the molecular weight and the saponification degree of the raw material polyvinyl alcohol.

(Example 2) Optical observation of polyvinyl alcohol film The untreated PVA film, degraded PVA film, and enzyme-treated degraded PVA film prepared in Example 1 were observed with a digital microscope (500 times). The observation image is shown in FIG. In FIG. 1, digital microscope images of an untreated PVA film, a degraded PVA film, and a degraded PVA film subjected to enzyme treatment are shown in order from the left. As shown in FIG. 1, the degraded PVA film subjected to the enzyme treatment has been whitened due to the degradation, and the black portion of the base can be clearly seen. Therefore, the degraded PVA film is decomposed by the enzyme solution treatment. It has been confirmed that. In addition, it was confirmed that many cracks are formed on the surface of the deteriorated PVA film.

(Example 3) Enzymatic treatment of a deteriorated PVA film on the surface of a gold foil A deteriorated PVA film was prepared in the same manner as in Example 1 except that the PVA film was prepared by applying the polyvinyl alcohol A aqueous solution to the gold foil surface. To the obtained PVA film, the enzyme solution prepared in Example 1 was dropped and allowed to stand at room temperature for 5 minutes. As Comparative Example 1, the same procedure was performed except that water was dropped instead of the enzyme solution. The result is shown in FIG. FIG. 2 is an image showing a state in which the PVA film on the gold foil surface is peeled off with tweezers after being left for 5 minutes, the right side is an image when an enzyme solution is dropped, and the left side is an image when water is dropped. It is. As shown in FIG. 2, when only water was dropped, the deteriorated PVA film could not be peeled off from the gold foil, and the deteriorated PVA film was pulled and the gold foil was pulled and wrinkles were formed. On the other hand, by dropping the enzyme solution, the deteriorated PVA film could be peeled off successfully without pulling up the underlying gold foil. Moreover, even if the treatment with the enzyme solution was performed, no change such as discoloration or fading was observed in the gold foil. Thereby, from the gold foil surface by performing the treatment with the enzyme solution. It was confirmed that only the PVA film could be removed without causing wrinkles or discoloration of the gold foil.

(Example 4) Enzymatic treatment of fragments of cultural assets Some of the paintings that have deteriorated in actual cultural assets have some small fragments falling. The fallen object was used as a sample and treated with an enzyme solution. Note that a PVA film was formed on the surface of the sample (falling object), and the PVA film was deteriorated and whitened. The enzyme solution prepared in Example 1 was dropped on the surface of the sample, allowed to stand at room temperature for about 5 minutes, and then washed with distilled water. The result is shown in FIG. In FIG. 3, the left side shows an image before the enzyme treatment, and the right side shows an image after the enzyme treatment. As shown in FIG. 3, by performing the treatment using the enzyme solution, the deteriorated PVA film which has been whitened due to deterioration over time and contracted to become wrinkled and blackened, is decomposed without affecting the pigment or the like. I was able to remove it.

  The present invention is extremely useful in terms of restoration, preservation, and conservation of cultural properties.

Claims (10)

A cultural property comprising contacting a cultural property that has been repaired with polyvinyl alcohol, an enzyme that can oxidize polyvinyl alcohol, and an enzyme composition that includes an enzyme that can hydrolyze the oxidized polyvinyl alcohol. Of removing polyvinyl alcohol from the water. The enzyme capable of oxidizing polyvinyl alcohol includes secondary alcohol oxidase (EC 1.1.3.18), and the enzyme capable of hydrolyzing oxidized polyvinyl alcohol is β-diketone hydrolase (EC 3). 7. The removal method according to claim 1, further comprising: 7.1.7). The removal method according to claim 1 or 2, wherein the polyvinyl alcohol includes at least one selected from the group consisting of a part that has deteriorated over time, a part that is insoluble in water, and a part that has been whitened. . The said enzyme composition is the removal method in any one of Claim 1 to 3 containing the enzyme composition obtained by the culture solution or culture | cultivation of the bacteria which have polyvinyl alcohol-degrading enzyme production ability, or a bacterial flora. The removal method according to any one of claims 1 to 4, wherein the cultural property is selected from the group consisting of a painting, a barrier painting, and a structure. The removal method according to any one of claims 1 to 5, comprising washing the cultural property brought into contact with the enzyme composition with water. The said polyvinyl alcohol is a film form, Comprising: The removal method in any one of Claim 1 to 6 including peeling the said film form polyvinyl alcohol from the said cultural property. A method for restoring a cultural property, comprising removing polyvinyl alcohol from the cultural property by the removing method according to claim 1. Polyvinyl alcohol containing at least one part selected from the group consisting of an aged part, a water-insoluble part and a whitened part can be hydrolyzed with an enzyme capable of oxidizing polyvinyl alcohol and an oxidized polyvinyl alcohol. A method for decomposing polyvinyl alcohol, comprising contacting an enzyme composition comprising an enzyme. A reagent for the restoration of cultural properties, comprising an enzyme capable of oxidizing polyvinyl alcohol and an enzyme capable of hydrolyzing oxidized polyvinyl alcohol.