JP5191680B2 - Binder for heat-developable photosensitive material - Google Patents

Description

  The present invention relates to a binder for a heat-developable photosensitive material.

  It is well known that a polyvinyl butyral resin is used as a binder, and in recent years, it has been frequently used as a binder for heat-developable photosensitive materials (Patent Documents 1 and 2). This polyvinyl butyral resin has a small apparent specific gravity obtained by reacting polyvinyl alcohol and butyraldehyde in water and / or an organic solvent in the presence of an acid catalyst, followed by washing, devolatilization and drying. It is a powdered resin. Here, in the production of the polyvinyl butyral resin, the devolatilized polyvinyl butyral resin is generally dried by employing a fluidized drying method or an airflow drying method. However, the polyvinyl butyral resin that is subjected to drying has a small apparent specific gravity, and there is a risk of dust explosion by scattering in the dry air flow, so it is necessary to take measures such as circulating nitrogen throughout the drying atmosphere. For this reason, there is a problem that the manufacturing cost becomes high and the operation management becomes difficult. In addition, since the apparent specific gravity of polyvinyl butyral resin is small, there is a problem that the volume of the storage used for storage becomes excessive compared to the weight, further increasing the transportation cost, and further, when processing polyvinyl butyral resin, There was a problem that productivity was lowered due to deterioration of workability and work environment.

  In the pamphlet of International Patent Publication No. 2005/019312 (Patent Document 3), a polyvinyl butyral resin obtained by butyralizing polyvinyl alcohol with butyraldehyde is extruded into a strand shape using a melt extruder, and cut into a desired shape. It is disclosed that a polyvinyl butyral resin pellet is obtained, and that the pellet is used as a binder for a heat-developable photosensitive material. However, Patent Document 3 does not disclose the influence of butyraldehyde and 2-ethyl-2-hexenal contained in the pellets on the binder characteristics of the heat-developable photosensitive material.

JP 2006-47974 A (Claims, [0006]) JP 2006-30959 A (Claims, [0009], [0010], [0027], [0030], [0051] to [0061]) International Patent Publication No. 2005/019312 (Patents, [0030], [0166])

  The present invention is capable of producing a photothermographic material that does not adversely affect image formation and does not deteriorate image characteristics, and that produces little odor when handled. The object is to provide a binder of the material.

According to the present invention, the above object is achieved by a binder for heat-developable photosensitive material obtained from a polyvinyl butyral resin pellets, the polyvinyl butyral resin pellet, washed polyvinyl butyral resin powder, water content 0.01 Obtained by melting and kneading using a melt extruder having a vent portion for devolatilization, which is dried to ˜6% by weight and equipped with a decompression means , and butyraldehyde and 2-ethyl-2- It has been found that the problem can be solved by a binder of a heat-developable photosensitive material having a hexenal content of 100 ppm or less.

Furthermore, the said objective is achieved more suitably by the polyvinyl butyral resin pellet having an acid value of 0.7 mgKOH / g or less.
Furthermore, the said objective is achieved more suitably by the said polyvinyl butyral resin pellet having a size of 0.5-2.5 mm.

  The binder of the heat-developable photosensitive material of the present invention does not adversely affect image formation when an image is formed on a heat-developable photosensitive material produced using the same, and image characteristics deteriorate. In addition, it has the characteristics that almost no odor is generated during handling, the apparent specific gravity is large, and the solvent solubility in a high concentration region is excellent.

In the present invention, it is important that the content of butyraldehyde and 2-ethyl-2-hexenal in the polyvinyl butyral resin pellet is 100 ppm or less, preferably 70 ppm or less, more preferably 50 ppm or less. By satisfying this condition, the binder of the heat-developable photosensitive material that is the object of the present invention can be obtained, as will be apparent from the examples described later. The content of butyraldehyde and 2-ethyl-2-hexenal means the content of butyraldehyde or 2-ethyl-2-hexenal alone or the total content of both. Here, 2-ethyl-2-hexenal is a dimer of butyraldehyde obtained in the process of producing a polyvinyl butyral resin.
Although 2-ethyl-2-hexenal is devolatilized by an extruder, the preferred content of 2-ethyl-2-hexenal is 60 ppm or less, and more preferably 20 ppm or less.
The preferred content of butyraldehyde is preferably 80 ppm or less, more preferably 60 ppm or less, and most preferably 40 ppm or less.
Further, butyraldehyde and 2-ethyl-2-hexenal are preferably as low as possible, but are usually 10 ppm or more, particularly 5 ppm or more.

  Further, in the binder of the photothermographic material of the invention, it is more preferable that the acid value of the polyvinyl butyral resin pellet is 0.7 mgKOH / g or less in order to achieve the object of the invention. More preferably, it is 0.5 mgKOH / g or less, and most preferably 0.25 mgKOH / g or less.

  Furthermore, the binder of the photothermographic material of the present invention preferably has a polyvinyl butyral resin pellet size of 0.5 to 2.5 mm, more preferably 0.7 to 2 mm. . Here, the size means that when the shape of the resin pellet is cylindrical, the diameter is 0.5 to 2.5 mm and the length is 0.5 to 2.5 mm. In the case of a sphere, the diameter is 0. In the case of an elliptical shape, it means that the major axis length and minor axis length are both 0.5 to 2.5 mm. By satisfying this condition for the size of the pellet, the polyvinyl butyral resin pellet intended by the present invention can be obtained more suitably, particularly to obtain a polyvinyl butyral resin pellet excellent in solvent solubility in a high concentration region. Can do.

Polyvinyl butyral resin pellets satisfying the above conditions can be obtained by melting polyvinyl extruded resin powder using a melt extruder, extruding, cooling and cutting, or extruding into water and then cutting. It is done.
More preferably, the polyvinyl butyral resin powder obtained by butyralizing a vinyl alcohol polymer with butyraldehyde has a water content of 0.01 to 6% by weight, preferably 0.5 to 5% by weight, More preferably, it is adjusted to 1 to 4% by weight, melted by using a melt extruder having a devolatilizing vent portion provided with at least one decompression means, extruded, cooled and cut, Or it is obtained by extruding into water and then cutting. What is particularly important here is that the polyvinyl butyral resin is adjusted to a water content of 0.01 to 6% by weight and then introduced into a melt extruder.

  In the present invention, the polyvinyl butyral powder that is a raw material of the polyvinyl butyral resin pellet is obtained by converting a vinyl alcohol polymer {for example, polyvinyl alcohol (PVA)} into a butyral. The vinyl alcohol polymer can be obtained by a known method, for example, by saponifying a polymer obtained by polymerizing a vinyl ester monomer. As a method for polymerizing the vinyl ester monomer, known methods such as a solution polymerization method, a bulk polymerization method, a suspension polymerization method, and an emulsion polymerization method can be applied. At that time, as the polymerization initiator, an azo initiator, a peroxide initiator, a redox initiator, or the like may be appropriately selected according to the polymerization method. For the saponification, a known method such as a method of alcoholysis using an alkali catalyst or an acid catalyst, a method of hydrolysis, etc. can be applied. Among them, methanol is used as a solvent and caustic soda (NaOH) as a catalyst. Since the method using is simple, it is preferable.

  Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, and palmitic acid. Vinyl, vinyl stearate, vinyl oleate, vinyl benzoate or the like may be used, and among these, vinyl acetate is preferably used.

  A vinyl alcohol polymer obtained by saponifying a polymer obtained by polymerizing a vinyl ester monomer differs in the content of each unit depending on the degree of saponification. And vinyl ester units derived from the monomer. For example, when vinyl acetate is used as the vinyl ester monomer, the vinyl alcohol polymer obtained by the above production method includes a vinyl alcohol unit and a vinyl acetate unit.

  When the above vinyl ester monomer is polymerized, other monomers may be copolymerized within a range not impairing the gist of the present invention. Examples of these other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutylene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, and i-acrylate. Acrylic acid esters such as propyl, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, Methacrylic acid such as ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate Acid S Acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salt, acrylamidopropyldimethylamine and its salt and its quaternary salt, N-methylol Acrylamide derivatives such as acrylamide and derivatives thereof; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and salts thereof, methacrylamidepropyldimethylamine and salts thereof and quaternary salts thereof, N-methylol Methacrylamide derivatives such as methacrylamide and derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-pro Vinyl ethers such as pyr vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; Using vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts and esters and anhydrides thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like May be. These monomers may be used in a proportion of usually less than 10 mol% with respect to the vinyl ester monomer.

  The butyralization of the vinyl alcohol polymer may be performed based on a known method. For example, the vinyl alcohol polymer and butyraldehyde may be mixed in the presence of an acid catalyst. The acid catalyst is not particularly limited, and any of organic acids and inorganic acids may be used. For example, acetic acid, paratoluenesulfonic acid, nitric acid, sulfuric acid, hydrochloric acid, etc. may be used. Of these, methods using hydrochloric acid, sulfuric acid and nitric acid are common, and hydrochloric acid is particularly preferred.

  Polyvinyl butyral is polyvinyl butyral obtained by butyralizing a vinyl alcohol polymer with n-butyraldehyde, but aldehydes having 2 to 6 carbon atoms other than butyraldehyde such as acetaldehyde, propionaldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde and the like can also be used in combination.

The following method is mentioned as a more detailed manufacturing method of the polyvinyl butyral powder used by this invention.
First, after adjusting an aqueous solution (concentration 3 to 15% by weight) of a vinyl alcohol polymer to a temperature range of about 80 to 100 ° C, the temperature of the aqueous solution is gradually changed to a temperature range of about -10 to 30 ° C. (Usually in about 10 to 60 minutes). Next, butyraldehyde used for butyralization and a butyralization catalyst such as an acid catalyst are mixed with the aqueous solution in a temperature range of about −10 to 30 ° C., and the temperature is kept constant for about 30 to 300 minutes. After allowing the butyralization reaction to proceed, the temperature is further raised to a temperature range of about 30 to 80 ° C. over 30 to 200 minutes, and this temperature range is maintained for about 1 to 8 hours. Next, after neutralizing with water, alkali or the like, the polyvinyl butyral powder can be obtained by drying.

  Next, the polyvinyl butyral powder obtained in this way was adjusted to a moisture content of 0.01 to 6% by weight as described above, and was further equipped with at least one decompression means for devolatilization. By melt-kneading using a melt-extruder having the above, organic carboxylic acid, butyraldehyde, 2-ethyl-2-hexenal, and the like can be removed, and the desired polyvinyl butyral resin pellets can be obtained.

  Here, as the melt extruder having a devolatilizing vent section provided with at least one decompression means, a melt extruder having a plurality of, for example, two vents is suitable. Examples of the melt extruder include a single screw type melt extruder and a twin screw type melt extruder.

As a method for adjusting the polyvinyl butyral powder introduced into the melt extruder to a moisture content of 0.01 to 6% by weight, for example, after washing the obtained polyvinyl butyral powder, a drying temperature of 50 ° C. to 90 ° C., Examples include a method of fluidized drying or airflow drying in a range of 60 minutes to 90 minutes, or a method of humidity control.
The preferred moisture content of the polyvinyl butyral powder introduced into the melt extruder is preferably 0.5% by weight or more for the lower limit, more preferably 1% by weight or more, and 5% by weight for the upper limit. The following is preferable, and more preferably 4% by weight or less.

  The polyvinyl butyral whose water content is adjusted in this way is melted in the range of a molten resin temperature to 280 ° C. in a melt extruder. The resin melted in the melt extruder is extruded and then cooled and cut, or extruded into water and then cut. As a method of extruding here, a method of extruding a molten resin in a strand shape is suitable. As a method of cutting after extrusion, a method of cutting with a cutter such as a rotary cutter is suitable.

  The polyvinyl butyral used in the present invention may contain other additives such as an antioxidant, a plasticizer, and an ultraviolet absorber as necessary. The timing for adding these additives may be before melting, during melting, or after melting.

  The ratio of residual acetyl groups in the polyvinyl butyral resin pellet of the present invention is preferably 0.1 to 30 mol%, and more preferably 0.5 to 15 mol%. Moreover, it is suitable that the ratio of the residual hydroxyl group of polyvinyl butyral is 10-50 mol%, More preferably, it is 15-40 mol%. Moreover, 40-85 mol% is suitable for the degree of butyralization of a polyvinyl butyral resin pellet, More preferably, it is 50-80 mol%. By satisfying these conditions of residual acetyl group, residual hydroxyl group and degree of butyralization, the object of the present invention can be achieved more suitably.

  The degree of polymerization of polyvinyl butyral is preferably 200 to 3000, and more preferably 300 to 1700. When the degree of polymerization is within this range, the moldability of the polyvinyl butyral resin pellet is good.

In addition, the content of halogen ions in the polyvinyl butyral resin pellet is preferably 100 ppm or less, and more preferably 80 ppm or less. Here, the halogen ion is derived from a halide used as a catalyst when producing polyvinyl butyral, and examples thereof include chloro ion.
The content of halogen ions in the polyvinyl butyral resin pellets can be adjusted by appropriately setting the washing method and the number of washings when washing polyvinyl butyral with water or a mixed solution of water / alcohol.

Further, the content of alkali metal ions in the polyvinyl butyral resin pellet is preferably 100 ppm or less, and more preferably 80 ppm or less. Here, the alkali metal ion is derived from the alkali metal compound used in the vinyl alcohol polymer production process and the polyvinyl butyral production process, and examples thereof include sodium ions and potassium ions.
The content of alkali metal ions in the polyvinyl butyral resin pellet is appropriately set with the washing method and the number of washings when washing the vinyl alcohol polymer and / or polyvinyl butyral with water or a mixed solution of water / alcohol. Can be adjusted.

  The polyvinyl butyral resin pellets thus obtained are useful as binders for photosensitive materials for heat development, and when an image is formed on a heat-developable photosensitive material produced using the same, it has a negative effect on image formation. In addition, the image characteristics are not deteriorated, and the odor is hardly generated at the time of handling.

  Usually, the heat-developable photosensitive material has a structure in which a photosensitive layer is laminated on a supporting substrate. The photosensitive layer has a composition in which polyvinyl butyral (polyvinyl butyral having different contents can be mixed and used) as a binder and an organic silver salt, a photosensitive silver halide salt, an organic reducing agent, etc. Consists of.

  The organic silver salt may be any light-stable, colorless or white silver salt that can react with an organic reducing agent to produce silver when heated in the presence of a photosensitive silver halide, Examples thereof include silver salts of organic compounds having a mercapto group, thione group, and carboxyl group, and benzotriazole silver salts. Specific examples include silver salt of 3-mercapto-4-phenyl 1,2,4-triazole, silver salt of 2-mercapto-benzimidazole, silver salt of 2-mercapto-5-aminothiazole, silver of thioglycolic acid Salt, silver salt of dithioacetic acid, silver salt of aliphatic carboxylic acid (caprine silver salt, silver laurate, silver myristate, silver palmitate, silver stearate, silver behenate, silver maleate, silver acetate, etc.) Can be mentioned.

Any photosensitive silver halide may be used as long as it acts on the organic silver salt to form silver halide.
The organic reducing agent is not particularly limited, and examples thereof include substituted phenols, bisphenols, naphthols, bisnaphthols, polyhydroxybenzenes, and hydroquinone monoethers.
In addition to this, a color toning agent, a color coupler, a leuco dye, a sensitizer and the like can be appropriately used for the photosensitive layer.

  As a method of laminating a photosensitive layer comprising these compositions on a supporting substrate, the above polyvinyl butyral resin pellets are dissolved in a solvent, and the above-described organic silver salt, photosensitive silver halide salt, organic reducing agent, etc. The method of apply | coating the mix | blended dispersion liquid to a support base material, and drying is mentioned. Examples of the solvent for the polyvinyl butyral resin include ketones such as acetone and methyl ethyl ketone, alcohols such as methanol, ethanol and butanol, and aromatic hydrocarbons such as toluene and xylene. The blending amount of the polyvinyl butyral resin in the solvent is 5 to 30% by weight, preferably 10 to 25% by weight, based on the weight of the solvent. The proportion of the polyvinyl butyral resin in the photosensitive layer (after removal of the solvent) is 10 to 90% by weight, preferably 30 to 70% by weight, based on the total weight of the photosensitive layer.

  Examples of the support substrate include polyester, polycarbonate, polyolefin (polyethylene, polypropylene, etc.), polyvinyl butyral, cellulose ester, a resin film such as cellulose triacetate, a metal plate such as an aluminum plate, glass, paper, and the like. Of these, a transparent resin film is preferred.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these Examples. In the following examples and comparative examples, “%” and “parts” mean “% by weight” and “parts by weight”, respectively, unless otherwise specified.
Various physical properties of the polyvinyl butyral (PVB) resin pellets prepared in Examples and Comparative Examples were measured according to the following methods.

(Content of vinyl acetate unit in PVB resin pellet)
Measured according to JIS K6728: 1977.

(Content of vinyl alcohol unit in PVB resin pellet)
Measured according to JIS K6728: 1977.

(Measurement of acid value in PVB resin pellet)
Measured according to JIS K6728: 1977.

(Contents of butyraldehyde and 2-ethyl-2-hexenal in PVB resin pellets)
Shimadzu headspace gas chromatography GC-14B and the column were measured using TC-1 (inner diameter 0.25 mm, length 30 m) manufactured by GL Science Inc.

(Content of halogen ion in polyvinyl butyral resin pellet)
The polyvinyl butyral resin pellet was dissolved in a mixed solution of ethanol / water, and then an aqueous silver nitrate solution was dropped, and the calculation was performed from the change point of conductivity obtained using a potentiometric titrator.

(Content of alkali metal ions in the polyvinyl butyral resin pellet)
Measurement was performed using an ICP emission element analyzer.

(Moisture content of PVB resin pellets)
The PVB resin pellets were dried at 105 ° C. for 3 hours using a dryer and calculated according to the following formula.
{(Weight of resin pellet before drying−weight of resin pellet after drying) / weight of resin pellet before drying} × 100 (%)
(Moisture content of PVB resin powder to be introduced into the extruder)
The PVB resin powder was dried at 105 ° C. for 3 hours using a dryer, and calculated according to the following formula.
{(Weight of resin powder before drying-Weight of resin powder after drying) / Weight of resin powder before drying} × 100 (%)

(Measurement of PVB resin pellet size)
About 30 PVB resin pellets taken out at random, the length and diameter were measured using calipers, and the average value was calculated. In the measurement, the MD direction was the length.

(Apparent specific gravity of PVB resin pellets)
Based on the specification of JIS K6721: 1994, the measurement was performed using a bulk specific gravity measuring instrument (manufactured by Tsutsui Riken).

(Solubility of PVB resin pellets)
1. Solubility in Low Concentration Region 10 g of PVB resin pellets were added to 90 g of ethanol with stirring to obtain an ethanol solution having a resin concentration of 10% by weight, and this was stirred at 20 ° C. with a mechanical stirrer at 200 rpm. The state of the resin pellet was visually observed, and the time until the resin pellet was completely dissolved was measured.
2. Solubility in High Concentration Region 20 g of PVB resin pellets were added to 80 g of ethanol with stirring to obtain an ethanol solution having a resin concentration of 20% by weight, and this was stirred at 20 ° C. using a mechanical stirrer at 200 rpm. The state of the resin pellet was visually observed, and the time until the resin pellet was completely dissolved was measured.

(Measurement of odor of PVB resin pellets)
At the time of manufacturing the resin pellets and at the time of handling the resin pellets, the odor of the PVB resin pellets was confirmed by a sensory test and evaluated according to the following criteria.
○: Almost no odor was felt ×: Odor was felt

(Storage stability of photosensitive agent coating solution)
The photosensitive agent coating solution was placed under an indoor fluorescent lamp at room temperature for 3 days and visually observed to confirm the color change of the solution, and evaluated according to the following criteria.
○: Almost no change in white color ×: Slight coloring was observed

(Sharpness of photosensitive film)
The photosensitive film was exposed to a high-pressure mercury of 250 watts at a distance of 20 cm for 0.3 seconds through a gradation pattern film, and then heated for 5 seconds using a 120 ° C. hot plate to obtain a cyan pattern image. . The obtained pattern images were evaluated according to the following criteria.
○: No fogging and good sharpness ×: Fogging occurs and sharpness is poor

(Preparation of PVB resin powder)
In a glass container having an internal volume of 2 liters equipped with a reflux condenser, a thermometer, and a squid type stirring blade, 1295 g of ion-exchanged water and 105 g of polyvinyl alcohol (PVA-1: polymerization degree 300, saponification degree 98 mol%). The whole was heated to 95 ° C. to completely dissolve PVA, and an aqueous PVA solution (concentration 7.5% by weight) was formed. The formed PVA aqueous solution was gradually cooled to 10 ° C. over about 30 minutes while continuing to stir at a rotational speed of 120 rpm, and then the aqueous solution was added with 58 g of butyraldehyde and an acid catalyst as a butyralization catalyst having a concentration of 20 The butyralization of PVA was started by adding 90 ml of weight% hydrochloric acid. After butyralization was performed for 150 minutes, the whole was heated to 50 ° C. over 60 minutes, held at 50 ° C. for 120 minutes, and then cooled to room temperature. After filtering the resin precipitated by cooling, it was washed with ion exchange water (100 times the amount of ion exchange water with respect to the resin), then added with 0.3 wt% sodium hydroxide solution for neutralization, and at 40 ° C. After holding for 10 hours, it was further washed again with 100 times the amount of ion-exchanged water, dehydrated, and then dried at 40 ° C. under reduced pressure for 18 hours to obtain a polyvinyl butyral (PVB-1) powder (water content of 1. 0%) was obtained.

(Preparation of PVB resin pellets)
As a melt-extrusion machine, an L / D = 54 co-rotating twin-screw type extruder (manufactured by Toshiba Machine Co., Ltd.) having two vent parts and having a reduced pressure of 0.08 MPa and 0.09 MPa from the hopper side is used. The powder of polyvinyl butyral (PVB-1) obtained above was introduced into this. After cooling the strand-shaped molten resin coming out of the die hole in a water tank, it is cut with a pelletizer, and a pellet-shaped polyvinyl butyral resin with a diameter of 1.6 mm and a length of 1.6 mm (water content 0.2 wt%) Got. The extrusion conditions of the molten resin were a screw rotation speed of 300 times / minute, a resin speed of 120 kg / hour, and a resin temperature of 200 ° C.
The polyvinyl butyral resin pellet had a butyralization degree of 68 mol%, a residual acetyl group (vinyl acetate unit) content of 2 mol%, and a residual hydroxyl group (vinyl alcohol unit) content of 30 mol%. The content of butyraldehyde is 16 ppm, the content of 2-ethyl-2-hexenal is 2 ppm, the content of halogen ions is 40 ppm, the content of alkali metal ions is 20 ppm, the apparent specific gravity is 0.61 g / cc, the acid The value was 0.20 mg KOH / g.
Table 1 shows the characteristics of the polyvinyl butyral resin pellet.

(Preparation of photosensitive agent coating solution)
5 g of the polyvinyl butyral resin pellets obtained above are dissolved in 40 g of methyl ethyl ketone, 5 g of silver behenate and 0.2 g of N-lauryl-1-hydroxy-2-naphthamide are further added thereto, and mixed for 24 hours with a ball mill. A photosensitive agent coating solution was obtained.
When the storage stability of the obtained photosensitive agent coating solution was evaluated, it remained white and hardly changed.
(Preparation of photosensitive film)
The photosensitive agent coating solution obtained above was applied onto a polyester substrate so that the thickness after drying was 10 μm and dried to obtain a photothermographic material. When drying after applying the photosensitive agent coating solution, almost no odor was felt.
On the coated surface of the heat-developable photosensitive material, a solution composed of 0.5 g of N, N-dimethyl-p-phenylenediamine / sulfate, 2 g of polyvinylpyrrolidone and 30 ml of methanol was applied so that the thickness after drying was 1 μm. And dried to obtain a photosensitive film.
When the sharpness of the obtained photosensitive film was evaluated, there was no fog and the sharpness was good.

A powder of polyvinyl butyral (PVB-2) (containing water) in the same manner as in Example 1 except that polyvinyl alcohol (PVA-2: polymerization degree 600, saponification degree 98 mol%) was used instead of PVA-1. 1.0% by weight).
After adjusting the water content of the polyvinyl butyral powder to 1.5% by weight, it was inserted into a melt extruder in the same manner as in Example 1 to obtain polyvinyl butyral resin pellets (water content 0.2% by weight). It was.
The obtained polyvinyl butyral resin pellets had a butyralization degree of 78 mol%, a vinyl acetate unit content of 2 mol%, and a vinyl alcohol unit content of 20 mol%. The content of butyraldehyde is 21 ppm, the content of 2-ethyl-2-hexenal is 4 ppm, the content of halogen ions is 50 ppm, the content of alkali metal ions is 20 ppm, the apparent specific gravity is 0.62 g / cc, the acid The value was 0.25 mg KOH / g. Table 1 shows the characteristics of the polyvinyl butyral resin pellet.
In the same manner as in Example 1, a photosensitive agent coating solution and a photosensitive film were prepared and evaluated for each. The evaluation results are shown in Table 1.

A polyvinyl butyral (PVB-3) powder (water content) in the same manner as in Example 1 except that polyvinyl alcohol (PVA-3: polymerization degree 1000, saponification degree 98 mol%) was used instead of PVA-1. Was 1.0 wt%).
After adjusting the water content of the polyvinyl butyral powder to 3% by weight, it was inserted into a melt extruder in the same manner as in Example 1 to obtain polyvinyl butyral resin pellets (water content 0.3% by weight).
The obtained polyvinyl butyral resin pellet had a butyralization degree of 68 mol%, a vinyl acetate unit content of 2 mol%, and a vinyl alcohol unit content of 30 mol%. The content of butyraldehyde is 40 ppm, the content of 2-ethyl-2-hexenal is 9 ppm, the content of halogen ions is 40 ppm, the content of alkali metal ions is 20 ppm, the apparent specific gravity is 0.61 g / cc, the acid The value was 0.35 mg KOH / g. Table 1 shows the characteristics of the polyvinyl butyral resin pellet.
In the same manner as in Example 1, a photosensitive agent coating solution and a photosensitive film were prepared and evaluated for each. The evaluation results are shown in Table 1.

A polyvinyl butyral (PVB-4) powder (water content) in the same manner as in Example 1 except that polyvinyl alcohol (PVA-4: polymerization degree 200, saponification degree 98 mol%) was used instead of PVA-1. Was 1.0 wt%).
After adjusting the water content of the polyvinyl butyral powder to 2% by weight, it was inserted into a melt extruder in the same manner as in Example 1 to obtain polyvinyl butyral resin pellets (water content 0.2% by weight).
The obtained polyvinyl butyral resin pellet had a butyralization degree of 68 mol%, a vinyl acetate unit content of 2 mol%, and a vinyl alcohol unit content of 30 mol%. The content of butyraldehyde is 30 ppm, the content of 2-ethyl-2-hexenal is 4 ppm, the content of halogen ions is 55 ppm, the content of alkali metal ions is 20 ppm, the apparent specific gravity is 0.63 g / cc, the acid The value was 0.20 mg KOH / g. Table 1 shows the characteristics of the polyvinyl butyral resin pellet.
In the same manner as in Example 1, a photosensitive agent coating solution and a photosensitive film were prepared and evaluated for each. The evaluation results are shown in Table 1.

Comparative Example 1
The polyvinyl butyral (PVB-1) powder obtained in Example 1 was used in the same manner as in Example 1 except that the degree of decompression of the extruder was 0.03 MPa. A content of 0.8% by weight) was obtained.
The obtained polyvinyl butyral resin pellet had a butyralization degree of 68 mol%, a vinyl acetate unit content of 2 mol%, and a vinyl alcohol unit content of 30 mol%. The butyraldehyde content is 71 ppm, the 2-ethyl-2-hexenal content is 62 ppm, the halogen ion content is 40 ppm, the alkali metal ion content is 20 ppm, the apparent specific gravity is 0.61 g / cc, and the acid The value was 0.9 mg KOH / g. Table 1 shows the characteristics of the polyvinyl butyral resin pellet.
In the same manner as in Example 1, a photosensitive agent coating solution and a photosensitive film were prepared and evaluated for each. The evaluation results are shown in Table 1.

Comparative Example 2
Polyvinyl butyral resin pellets (water content: 0.9% by weight) were obtained in the same manner as in Example 1 except that devolatilization was not performed when the molten resin was extruded.
The obtained polyvinyl butyral resin pellet had a butyralization degree of 68 mol%, a vinyl acetate unit content of 2 mol%, and a vinyl alcohol unit content of 30 mol%. The butyraldehyde content is 152 ppm, the 2-ethyl-2-hexenal content is 87 ppm, the halogen ion content is 40 ppm, the alkali metal ion content is 20 ppm, the apparent specific gravity is 0.61 g / cc, the acid The value was 1.2 mg KOH / g. The characteristics of polyvinyl butyral resin pellets are shown in Table 1. In the same manner as in Example 1, a photosensitive agent coating solution and a photosensitive film were prepared and evaluated for each. The evaluation results are shown in Table 1.

Comparative Example 3
Polyvinyl butyral resin pellets (water content 0.8 wt.%) In the same manner as in Example 1 except that the moisture content of the polyvinyl butyral (PVB-1) powder was adjusted to 15 wt% and introduced into the melt extruder. %).
The obtained polyvinyl butyral resin pellet had a butyralization degree of 68 mol%, a vinyl acetate unit content of 2 mol%, and a vinyl alcohol unit content of 30 mol%. The butyraldehyde content is 79 ppm, the 2-ethyl-2-hexenal content is 92 ppm, the halogen ion content is 40 ppm, the alkali metal ion content is 20 ppm, the apparent specific gravity is 0.61 g / cc, and the acid The value was 0.9 mg KOH / g. Table 1 shows the characteristics of the polyvinyl butyral resin pellet.
In the same manner as in Example 1, a photosensitive agent coating solution and a photosensitive film were prepared and evaluated for each. The evaluation results are shown in Table 1.

Comparative Example 4
When various physical properties of the polyvinyl butyral (PVB-1) powder obtained in Example 1 (water content: 1.0% by weight) were measured, the degree of butyralization was 68 mol%, and the residual acetyl group (acetic acid The content of vinyl units was 2 mol%, and the content of residual hydroxyl groups (vinyl alcohol units) was 30 mol%. The butyraldehyde content was 113 ppm, the 2-ethyl-2-hexenal content was 128 ppm, the halogen ion content was 40 ppm, the alkali metal ion content was 20 ppm, the apparent specific gravity was 0.21 g / cc, and the acid The value was 1.5 mgKOH / g. Table 1 shows the characteristics of the polyvinyl butyral (PVB-1) powder.
Using a powder of polyvinyl butyral (PVB-1), a photosensitive agent coating solution and a photosensitive film were prepared in the same manner as in Example 1, and each was evaluated. The evaluation results are shown in Table 1.

  The binder of the heat-developable photosensitive material of the present invention does not adversely affect image formation when an image is formed on a heat-developable photosensitive material produced using the same, and image characteristics deteriorate. In addition, there is almost no odor during handling, and it has a large apparent specific gravity and excellent solvent solubility in a high concentration region. It is extremely useful as a binder.

Claims (4)

A binder for heat-developable photosensitive material obtained from a polyvinyl butyral resin pellets, the polyvinyl butyral resin pellet, washed polyvinyl butyral resin powder was dried to a moisture content of 0.01 to 6 wt%, the pressure reducing means Heat obtained by melt- kneading using a melt extruder having at least one devolatilizing vent with a content of butyraldehyde and 2-ethyl-2-hexenal of 100 ppm or less Binder for developing photosensitive material.   The binder for a heat-developable photosensitive material according to claim 1, wherein the polyvinyl butyral resin pellet has an acid value of 0.7 mgKOH / g or less.   The binder of a photothermographic material according to claim 1 or 2, wherein the polyvinyl butyral resin pellet has a size of 0.5 to 2.5 mm.   The polyvinyl butyral resin pellet has a residual acetyl group ratio of 0.1 to 30 mol%, a residual hydroxyl group ratio of 10 to 50 mol%, a butyralization degree of 40 to 85 mol%, and a polymerization degree of 200 to 3000. The binder of the heat developable photosensitive material of any one of -3.