JP7581666B2 - Hydroquinone flakes - Google Patents

Description

The present invention relates to a group of hydroquinone flakes.

Hydroquinone is widely used as a polymerization inhibitor or antioxidant.
Patent Document 1 describes a method in which hydroquinone is dissolved in hot water, the solution is broken down into droplets, and the droplets are brought into contact with cold gas to be processed into beads having a particle size of 100 μm to 3000 μm.
Patent Document 2 describes that hydroquinone flakes having a specific length, width, thickness and a specific bulk density can be obtained by spraying molten hydroquinone, depositing it on a cylinder and solidifying it, and then rotating the cylinder to drop the solidified hydroquinone.

Patent No. 4909515 Patent No. 5676101

When hydroquinone is used as a polymerization inhibitor or an antioxidant, it is desired that it has a high dissolution rate in order to dissolve it in water or an organic solvent, which is a solvent.
Furthermore, when hydroquinone is in the form of a fine powder, it becomes charged and is easily affected by static electricity, which makes it difficult to handle.
The hydroquinone beads described in Patent Document 1 have the problem that they require special equipment in the manufacturing process and cannot use existing equipment. In addition, there is a problem that hydroquinone dust is generated when the droplets are broken down into small pieces. Furthermore, it takes time to dissolve in water or an organic solvent.
The hydroquinone flakes described in Patent Document 2 have a low ratio of fine powder immediately after production, and because of their thin thickness, the ratio of fine powder increases due to collapse during transportation and storage, resulting in significant dust problems. Also, there is a problem of easy blocking.
An object of the present invention is to obtain hydroquinone flakes which have a low fine powder rate, a dissolution time in water within a practical range, and are less susceptible to blocking.

The present invention includes, for example, the following [1] to [15].
[1] A group of hydroquinone flakes,
A population of hydroquinone flakes having an average flake length in the range of 2.0 mm to 45.0 mm, an average flake width in the range of 2.0 mm to 30.0 mm, and an average flake thickness in the range of 1.6 mm to 3.5 mm.
[2] The hydroquinone flakes according to [1], wherein the fine powder rate in the flakes is less than 1% by mass.
[3] A group of hydroquinone flakes according to [2], in which the fine powder content in the group of flakes immediately after production is less than 0.5 mass%.
[4] A group of hydroquinone flakes according to any one of [1] to [3], wherein the average flake length in the group of flakes is in the range of 5.0 mm to 30.0 mm.
[5] A group of hydroquinone flakes according to any one of [1] to [4], wherein the average flake width in the group of flakes is in the range of 2.0 mm to 16.0 mm.
[6] A group of hydroquinone flakes according to any one of [1] to [5], wherein the average flake thickness in the group of flakes is in the range of 1.6 mm to 3.0 mm.
[7] The group of hydroquinone flakes according to any one of [1] to [6], wherein the maximum thickness of the flakes is in the range of 2.0 mm to 4.0 mm.
[8] The group of hydroquinone flakes according to any one of [1] to [7], wherein the group of hydroquinone flakes has a cumulative specific surface area of 10 m ² /g or more.
[9] The group of hydroquinone flakes according to [8], wherein the cumulative specific surface area of the flakes is in the range of 13 m ² /g to 15 m ² /g.
[10] The group of hydroquinone flakes according to any one of [1] to [9], wherein the group of hydroquinone flakes has a cumulative pore volume of 0.04 ml/g or more.
[11] The hydroquinone flake group according to [10], wherein the cumulative pore volume of the flake group is in the range of 0.05 ml/g to 0.20 ml/g.
[12] The group of hydroquinone flakes according to any one of [1] to [11], wherein the group of flakes has a Hausner ratio of 1.5 or less.
[13] The group of hydroquinone flakes according to any one of [1] to [12], wherein the degree of compression of the group of flakes is 33% or less.
[14] The group of hydroquinone flakes according to any one of [1] to [13], wherein the flakes have a crushing strength of 15 N or less or do not aggregate.
[15] A polymerization inhibitor using hydroquinone flakes according to any one of [1] to [14].

The hydroquinone flakes of the present invention have a low fine powder rate, a dissolution time in water within a practical range, and are less prone to blocking.

FIG. 1 is a schematic diagram showing an example of a steel belt flaker. FIG. 1 is a schematic diagram illustrating an example of a drum flaker. FIG. 1 is a schematic diagram illustrating an example of a drum flaker. 1 is an optical microscope photograph of an example flake.

In this specification,
"Flake" refers to a particle having a ratio of thickness to length (thickness/length) defined below in the range of 0.030 to 1.000.
The shape of the "flakes" is not particularly limited and includes various shapes such as a sphere, an ellipse, a rectangular parallelepiped, and a polygon.
"Hydroquinone flakes" refers to an aggregate of hydroquinone flakes. Hereinafter, this will also be referred to as "flakes".

The "length,""width," and "thickness" of a flake are defined as follows:
When one flake is stored in a parallelepiped so that each of the inner faces of the parallelepiped is in contact with one or more points, the longest side of the three mutually orthogonal sides of the parallelepiped is called the "length," the second longest side is called the "width," and the shortest side is called the "thickness." The side values are measured with a vernier caliper scale of 0.01 mm and rounded off to one decimal place.

The hydroquinone flakes are obtained with a distribution of flake length, width and thickness.
The average flake length in a group of flakes, the average flake width in a group of flakes, and the average flake thickness in a group of flakes refer to the average length, the average width, and the average thickness of any 10 flakes in a group of flakes, respectively. In this specification, one or more of the average length, average width, average thickness, and maximum thickness of a single flake in a group of flakes may also be referred to as a flake dimension.

"Maximum thickness" refers to the maximum thickness among the thicknesses of any 10 flakes in a group of flakes.
In this specification, the term "fine powder" refers to disintegrated flakes that pass through a sieve with 105 μm openings.

FIG. 4 shows an example of one flake.
The average length of a single flake in the group of flakes is in the range of 2.0 mm to 45.0 mm, preferably in the range of 5.0 mm to 30.0 mm, and more preferably in the range of 5.0 mm to 25.0 mm.
The average width of a single flake in the group of flakes is in the range of 2.0 mm to 30.0 mm, preferably in the range of 2.0 mm to 16.0 mm, and more preferably in the range of 5.0 mm to 13.0 mm.
The average thickness of a single flake in the population of flakes is in the range of 1.6 mm to 3.5 mm, preferably in the range of 1.6 mm to 3.0 mm, and more preferably in the range of 1.6 mm to 2.5 mm.
The maximum thickness of the flakes in the population of flakes is in the range of 2.0 mm to 4.0 mm, preferably in the range of 2.0 mm to 3.5 mm, and more preferably in the range of 2.0 mm to 3.0 mm.
It is preferable that the average length, average width, average thickness, and maximum thickness of a single flake group are within the above-mentioned ranges, since this makes it possible to suppress both an increase in the dissolution time in water and an increase in the fine powder rate.

The cumulative specific surface area of the flakes measured by mercury intrusion porosimetry is preferably 10 m ² /g or more, more preferably in the range of 13 m ² /g to 15 m ² /g, and even more preferably in the range of 13 m ² /g to 14 m ² /g.
The cumulative pore volume of the flakes measured by mercury intrusion porosimetry is preferably 0.04 ml/g or more, more preferably in the range of 0.05 ml/g to 0.20 ml/g, and even more preferably in the range of 0.06 ml/g to 0.15 ml/g.
If the cumulative specific surface area and cumulative pore volume are within the above ranges, it is assumed that nano-order pores that can be impregnated with a solvent such as water can be formed while suppressing an increase in the fine powder ratio, thereby increasing the contact area with the solvent, which is preferable from the viewpoint of shortening the dissolution time.
The cumulative specific surface area and cumulative pore volume are measured by the methods described in the Examples.

The bulk density of the flakes is preferably 0.3 g/ml to 0.7 g/ml, more preferably 0.4 g/ml to 0.6 g/ml.
The tap density of the flakes is preferably 0.5 g/ml to 0.8 g/ml, more preferably 0.6 g/ml to 0.7 g/ml.
If the bulk density and tap density are within the above ranges, the powder has good flowability. That is, if the Hausner ratio (tap density/bulk density) is 1.5 or less, the transport efficiency in piping or the like can be improved, and it is preferably 1.3 or less, and more preferably 1.27 or less.
Furthermore, when the bulk density and tap density are within the above ranges, the compressibility, which is an index of powder compressibility {(tap density-bulk density)/tap density x 100}, is preferably 33% or less from the viewpoint of improving the efficiency of filling containers such as silos and hoppers, more preferably 25% or less, and even more preferably 22% or less.
The bulk density and tap density are values measured by the measurement methods described in the Examples.

The fine powder ratio in 100% by mass of the flake group is preferably less than 1% by mass, more preferably less than 0.5% by mass, and even more preferably less than 0.2% by mass. The fine powder ratio refers to the ratio (% by mass) of the mass of the fine powder that passed through a sieve with a mesh size of 105 μm to the mass of the entire flake group.
If the flakes are subjected to impact during transportation or storage, they may break down and generate fine powder. The fine powder rate is the percentage of fine powder contained in the flakes before such fine powder is newly generated. Specifically, it is measured immediately after the flakes are produced by the production method described below.

When dissolving hydroquinone flakes in water, the time required to completely dissolve 1.44 g of hydroquinone flakes in 28.56 g of pure water at 25°C and a rotation speed of 600 rpm, i.e., the dissolution time required to prepare an aqueous solution with a hydroquinone concentration of 4.8% by mass, is preferably 30 minutes or less, more preferably 5 to 20 minutes, and even more preferably 5 to 15 minutes. Thus, the flakes of the present invention have a suitable dissolution time in water, despite the flakes having larger flake dimensions than conventional hydroquinone flakes.

From the viewpoint of suppressing blocking, the crushing strength is preferably 15N or less or no aggregation, more preferably 10N or less or no aggregation, even more preferably 5N or less or no aggregation, and most preferably no aggregation. However, if three or more flakes are not aggregated, it is determined that there is no aggregation. The crushing strength is a value measured using the measurement method described in the examples.

<Method of producing hydroquinone>
Hydroquinone is usually obtained by oxidizing phenol or a hydroxyl-protected compound thereof with a peroxide or the like. Specifically, it can be obtained by the production method described in, for example, WO 2019/182035.

<Method of manufacturing flakes>
As a method for producing hydroquinone flakes, a general flake device such as a drum flaker, a table flaker, a steel belt flaker, a double steel belt flaker, etc. is selected. There is no particular limitation. Thus, the hydroquinone flakes of the present invention can be produced using known devices described in JP 2012-82158 A, JP 5837755 A, etc.

For example, if a steel belt flaker is used, the hydroquinone melt is continuously extruded from a nozzle at the tip of the extruder to form a plate- or string-shaped hydroquinone melt (hereinafter also referred to as "melt"). The amount of liquid sent can be, for example, the amount described in the Examples. The nozzle may have a single hole or multiple holes. The shape of the nozzle hole is appropriately selected according to the cross-sectional shape of the desired melt, and can be any shape, such as a circle, ellipse, diamond, or rectangle.

The molten liquid extruded from the nozzle is supplied onto a metal belt that functions as a metal belt cooler, and is cooled and solidified by the metal belt. The material, belt length, belt width, etc. of the metal belt can be determined by referring to the contents of the examples. The metal belt cooler has an endless metallic conveyor belt (metal belt), and is a device in which this endless conveyor belt is cooled by a cooling mechanism provided on the inner circumference side, and the material to be cooled is supplied to the outer circumference side of this endless conveyor belt to cool the material to be cooled. The cooling temperature is preferably 5 to 50°C, and more preferably 10 to 30°C. The cooling temperature is the temperature of a cooling medium such as cooling water or the temperature of the endless conveyor belt.

There is no particular limitation on the type of metal belt cooler, and for example, as shown in Fig. 1, the molten liquid 2 extruded from a nozzle 1 of a melt extruder is sandwiched between two metal belts 3, 4 and transported to the end of the belts. The two metal belts 3, 4 are cooled by spraying cooling water from cooling mechanisms 5, 6. In the metal belt cooler, the cooling water does not come into contact with the molten liquid 2, and the molten liquid 2 is cooled via the metal belts 3, 4, so there is no risk of the molten liquid 2 absorbing moisture when it is cooled.
As shown in FIG. 1, the metal belt cooler may be provided with a press roller 11 for rolling the molten liquid 2 or the like.

The metal belt cooler is not limited to the one shown in FIG. 1, and it is also possible to use a single belt cooler that cools the molten liquid using a single metal belt. However, a double cooler system that clamps and cools the molten liquid from two directions is preferable in terms of cooling efficiency, etc.

The plate- or string-shaped hydroquinone solidified material (hereinafter also referred to as "solidified material") obtained by the above-mentioned molten liquid solidification process is cut to the desired length of hydroquinone flakes, or the solidified material is crushed and fragmented by a crusher 21. Note that FIG. 1 shows an example in which the solidified material is crushed by a crusher 21 to produce hydroquinone flakes 22.

When cutting a solidified material, the cut is usually made perpendicular to the length of the solidified material.

The device used to cut the solidified material may be any device equipped with a cutter for cutting the solidified material, such as a scraper blade that scrapes off plate-like or string-like solidified material by grounding the blade against the edge of a belt, or a pelletizer that cuts with a rotating blade and a fixed blade.

The drum flaker is shown in FIGS.
Molten hydroquinone is provided in the supply tanks 35 and 42. The supply tanks 35 and 42 are equipped with temperature control devices to keep the hydroquinone in a molten state. The temperature of the molten hydroquinone is usually 172°C to 220°C. In FIG. 2, a part of the cooling drum 30 is immersed in the supply tank 35 as shown in FIG. 2. The immersion depth of the cooling drum 30 in the supply tank 35 is usually 1 mm to 5 mm. The cooling drum 30 rotates, and the molten hydroquinone is attached to its surface by the rotation to form a thin film 36. Alternatively, as shown in FIG. 3, the molten hydroquinone is transferred from the supply tank 42 to the liquid supply nozzle 45 by using a pump 43, and is supplied from the liquid supply nozzle 45 to the outer surface of the cooling drum 40, and the molten hydroquinone is attached to the outer surface of the cooling drum, and the thin film 46 is formed by the rotation. The cooling drum may be, for example, a vertical or horizontal metal pressure vessel, as well as a general-purpose metal drum or a resin drum. The cooling drum is preferably made of a heat-conductive material or is coated with a heat-conductive material. The dimensions of the cooling drum are not particularly limited, but are generally about 0.5 m to 1.0 m.

The hydroquinone is solidified by cooling the cooling drums 30 and 40. The cooling method is not particularly limited, but examples include a method of circulating water through the jacket and a method of spraying water, water vapor, or a refrigerant onto the inner surfaces of the cooling drums 30 and 40 from the cooling water spray nozzles 34 and 44. The cooling temperature is preferably 5°C to 50°C.

The solidified hydroquinone is collected in flakes 38 and 48 by any known means, such as by gravity, using scraper blades 37 and 47 to peel the solidified films 36 and 46 from the cooling drums 30 and 40. The collected hydroquinone flakes 38 and 48 are removed from the chambers 31 and 41 by a conveyor 32 or the like.
The thickness of the flakes is determined by controlling the thickness of the thin films 36 and 46, that is, by controlling the feed rate of hydroquinone to the cooling drums 30 and 40, the rotational speed of the cooling drums, and the cooling temperature.

<Applications>
The hydroquinone flakes of the present invention are useful as organic synthesis intermediates or manufacturing raw materials, and are used in the fields of reducing agents, rubber chemicals, dyes, medicines, agricultural chemicals, polymerization inhibitors, oxidation inhibitors, etc., and are preferably used as polymerization inhibitors.

The present invention will be specifically explained using examples and comparative examples.

The dimensions and measurements shown in Table 1 for the flakes obtained in the Examples and Comparative Examples were measured by the following measuring methods.
<Measurement of flake size>
Ten flakes were randomly selected and their length, width, and thickness were measured using a caliper (with 0.01 mm scale). The average length, width, and thickness of the ten flakes were determined (hereinafter also referred to as "average length,""averagewidth," and "average thickness"). The maximum thickness among the thicknesses of the ten flakes was taken as the maximum thickness.

<Measurement of fine powder ratio>
The flakes were sieved through a sieve with 105 μm openings, and the ratio (mass %) of the mass of the fine powder that passed through the sieve to the total mass of the flakes was determined.
If the flakes are subjected to an impact during transportation or storage, the flakes may break down and generate fine powder. The fine powder content in this specification refers to the content of fine powder contained in the flakes before such fine powder is newly generated. Specifically, it was measured immediately after the flakes were produced.

<Measurement of bulk density>
100 g of the flakes were gently placed in a 250 ml measuring cylinder, and the mass per volume was calculated by reading the scale.

<Measurement of tap density>
100 g of the flakes were gently placed in a 250 ml graduated cylinder, the graduated cylinder was raised about 5 cm, and then dropped under its own weight onto a workbench to give vibration. This operation was repeated 100 times, and the scale was then read to calculate the mass per volume.

<Measurement of dissolution time>
1.44 g of the flakes and 28.56 g of pure water were placed in a 50 ml glass container, and the mixture was stirred at 600 rpm with a magnetic stirrer at 25° C., and the time it took for the flakes to completely dissolve was measured by visual inspection. The measured time was the time required to prepare a 4.8% by mass aqueous solution of hydroquinone.

<Measurement of cumulative specific surface area and cumulative pore volume>
The cumulative specific surface area and cumulative pore volume were measured by a mercury porosimeter using the mercury intrusion method (JIS R1655). The measurement device used was a fully automatic pore distribution measurement device PORE MASTER 60-GT manufactured by Quantachrome Instruments. Specifically, the flakes were placed in a sample container and degassed for 30 minutes at a pressure of 2.67 Pa or less, and then mercury was introduced into the sample container and gradually pressurized to inject mercury into the pores of the sample. Mercury was injected into the porous resin body from a pressure of 0.53 psia (about 3.68 kPa) corresponding to a pore diameter of 400 μm to a pressure of 60,000 psia (about 413 MPa) corresponding to a pore diameter of 3.6 nm, and the cumulative pore volume (mL/g) was calculated by dividing the total amount of mercury intrusion (mL) by the sample weight (g). The cumulative specific surface area was calculated by dividing the average pore diameter by the total amount of mercury injected, assuming that all pores were cylindrical.

<Measurement of crushing strength>
Water was sprayed uniformly onto the flakes to make them 10% hydrated, and a load of 0.18 kg/ ^cm2 was applied to the flakes, followed by a cycle of heating at 50°C for 9 hours and cooling at 25°C for 15 hours for a total of 5 days to produce an aggregate (solidified material) of flakes. The maximum resistance value at the time of aggregate collapse of the obtained aggregate of flakes was measured using ZTS-500N manufactured by Imada Co., Ltd., and this was taken as the crushing strength. However, if three or more flakes are not aggregated, it is judged that the aggregate is not aggregated. The higher the crushing strength, the more difficult it is to collapse the aggregate and the more likely it is to block. This is because it is affected by the dimensions and surface condition of the flakes.

[Example 1]
Hydroquinone melted at 180 to 200°C was fed from a feed nozzle at 320 kg/hr, and the hydroquinone melt was extruded onto the lower belt of a pair of 1650SM belt coolers (upper belt: belt width 650 mm, belt length 3 m, lower belt: belt width 600 mm, belt length 6 m), and cooling water at 15°C was sprayed onto the back of the belt, so that the melt was contact-solidified by the belt cooler. The solidified hydroquinone was cut by a scraper blade disposed at the end of the pair of belt coolers, and a group of hydroquinone flakes having an average length of 17.7 mm, an average width of 12.0 mm, and an average thickness of 1.6 mm was obtained.

[Example 2]
Solidified hydroquinone was obtained in the same manner as in Example 1, except that the cooling water temperature was changed to 17° C. The solidified flakes were cut with a scraper blade in the same manner as in Example 1, to obtain hydroquinone flakes having an average length of 11.4 mm, an average width of 6.2 mm, and an average thickness of 2.0 mm.

[Example 3]
Solidified hydroquinone was obtained in the same manner as in Example 1, except that the cooling water temperature was changed to 19° C. The solidified flakes were cut with a scraper blade in the same manner as in Example 1, to obtain hydroquinone flakes having an average length of 14.3 mm, an average width of 7.0 mm, and an average thickness of 2.2 mm.

[Example 4]
Solidified hydroquinone was obtained in the same manner as in Example 1, except that the cooling water temperature was changed to 25° C. The solidified flakes were cut with a scraper blade in the same manner as in Example 1, to obtain hydroquinone flakes having an average length of 24.3 mm, an average width of 15.2 mm, and an average thickness of 2.4 mm.

[Example 5]
Solidified hydroquinone was obtained in the same manner as in Example 1, except that the cooling water temperature was changed to 30° C. The solidified flakes were cut with a scraper blade in the same manner as in Example 1, to obtain hydroquinone flakes having an average length of 32.8 mm, an average width of 18.7 mm, and an average thickness of 2.7 mm.

[Comparative Example 1]
Hydroquinone melted at 187°C was immersed in the lower part of a cooling drum (drum diameter 0.63 m, drum width 0.3 m, drum circumference 1.98 m, drum rotation speed 10.3 rpm) to a depth of about 1 mm, and the hydroquinone was solidified by applying a saturated vapor refrigerant of 153°C for 2 seconds, and then peeled off with a scraper blade to obtain flakes of hydroquinone. The flakes had an average length of 7.3 mm, an average width of 5.5 mm, and an average thickness of 0.5 mm.

The values in Table 1 were determined as follows. The following values are per one flake.
Apparent volume (A): (A) = average length x average width x maximum thickness (ml)
Apparent weight (B): (B) = (A) x 1.33 (g)
(Density of hydroquinone is 1.33 g/ml (20° C.))
Actual volume (C): (C) = (A) - (B) x cumulative pore volume (ml)
Actual weight (D): (D) = (C) x 1.33 (g)
(Density of hydroquinone is 1.33 g/ml (20° C.))
Effective surface area (E): (E) = (D) x cumulative specific surface area (m ² )
Apparent volume ratio (F): (F) = (A) / 0.04
(The value of (A) in each Example was divided by the value of (A) in Comparative Example 1.)
Real surface area ratio (G): (G) = (E) / 0.35
(The value of (E) in each Example was divided by the value of (E) in Comparative Example 1.)
(G)/(F): This refers to the effect of increasing the contact area relative to the flake size. The larger (G)/(F) is, the greater the contact area of the flake size with the solvent is. Based on the comparative example, the greater the ratio is than 1.0, the greater the effect of shortening the dissolution time relative to the flake size.

The dissolution time is presumed to be a value corresponding to the flake size represented by the apparent volume, and although the apparent volumes of Examples 1 to 5 are 4.1 to 50.9 times larger than that of Comparative Example 1, the dissolution time is the same or at most increased by about 3 times. This is thought to be because the (G)/(F) values of Examples 1 to 5 are 1.5 to 1.6 times larger, and therefore an appropriate dissolution time was achieved despite the flake size being larger than that of the Comparative Example.
In comparison with Comparative Example 1, Examples 1 to 5 have lower Hausner ratios and compressibility, and therefore have excellent fluidity and packing efficiency, making them suitable for transportation and storage.
It can be seen that Examples 1, 2 and 5 have lower crushing strength or do not aggregate compared to Comparative Example 1, and therefore are less susceptible to blocking than Comparative Example 1.
It can be seen that, compared with Comparative Example 1, Examples 1 to 5 have a lower fine powder ratio, and therefore the flakes are less likely to disintegrate.

The hydroquinone flakes of the present invention are useful as various organic synthesis intermediates or manufacturing raw materials, and are used in fields such as reducing agents, rubber chemicals, dyes, medicines, agricultural chemicals, polymerization inhibitors, and oxidation inhibitors.

REFERENCE SIGNS LIST 1 nozzle 2 melt 3, 4 metal belt 5, 6 cooling mechanism 11 press roller 21 crusher 22 hydroquinone flakes 30 cooling drum 31 chamber 32 nitrogen 33 gas treatment device 34 cooling water spray nozzle 35 supply tank 36 thin film 37 scraper blade 38 hydroquinone flakes 39 conveyor 40 cooling drum 41 chamber 42 supply tank 43 pump 44 cooling water spray nozzle 45 liquid supply nozzle 46 thin film 47 scraper blade 48 hydroquinone flakes

Claims (7)

Hydroquinone flakes,
The average flake length in the flake group is in the range of 5.0 mm to 32.8 mm ;
The average flake width for the flake group is in the range of 2.0 mm to 18.7 mm ;
The average flake thickness for the group of flakes is in the range of 1.6 mm to 3.0 mm ;
The cumulative specific surface area of the flakes is in the range of 13 m ² /g to 15 m ² /g;
The cumulative pore volume of the flakes is 0.04 ml/g or more;
The Hausner ratio of the flakes is 1.5 or less;
Hydroquinone flakes. The hydroquinone flakes according to claim 1, wherein the fine powder content in the flakes is less than 1% by mass. The hydroquinone flakes according to claim 2, wherein the fine powder content in the flakes is less than 0.5% by mass. 4. The flakes of hydroquinone according to any one of claims 1 to 3 , wherein the maximum thickness of the flakes is in the range of 2.0 mm to 4.0 mm. 5. The flakes of hydroquinone according to any one of claims 1 to 4 , wherein the cumulative pore volume of the flakes is in the range of 0.05 ml/g to 0.20 ml/g. 6. Flakes of hydroquinone according to any one of claims 1 to 5 , wherein the degree of compression of the flakes is less than or equal to 33%. 7. The hydroquinone flakes according to claim 1 , wherein the flakes have a crushing strength of 15 N or less, or do not aggregate.