JP6834117B2 - Hydrolytic particles - Google Patents

Description

The present invention relates to hydrolyzable particles, and more particularly to hydrolyzable particles which are preferably used as additives added to a dispersion for excavation.

Hydrolyzable resins typified by polyoxalate and polylactic acid are also excellent in biodegradability, and from the viewpoint of environmental improvement, they are currently being studied as alternatives to various plastics in various applications. It has been put to practical use in the department.
Recently, it has also been proposed to use it as an additive added to the excavation liquid used for extracting underground resources (see Patent Documents 1 to 3).

For example, a well drilling method called hydraulic fracturing is currently widely adopted for the extraction of underground resources. In such an excavation method, a crack (fracture) is generated in the vicinity of the well by pressurizing the excavation liquid that fills the well at a high pressure, and the permeability (easiness of fluid flow) in the vicinity of the well is improved. The purpose is to expand the effective inflow section of resources such as oil and gas into the well and increase the productivity of the well. Such excavation fluid, also called fracturing fluid, used to be a viscous fluid such as gel-like gasoline in the past, but recently, shale gas produced from the shale gas layer existing in a relatively shallow place. With the development of such products, an aqueous dispersion in which polymer particles are dissolved or dispersed in water has come to be used in consideration of the influence on the environment. As such a polymer, a hydrolyzable resin such as polyoxalate or polylactic acid has been proposed.

That is, when the well is filled with an excavation liquid in which hydrolyzable particles are dispersed in water as described above and the pressure is applied to the well, the particles permeate into the vicinity of the well and a crack (fracture) already formed is formed. ) Can be used as a sealing material to temporarily block the flow path of resources such as gas and oil.
Generally, in order to create a crack in a well, a preliminary blast called perporation is performed in the horizontal well. Such a preliminary blast creates a number of small cracks in the depths of the well, along with relatively large cracks. After that, by press-fitting the excavation fluid (fracturing fluid) into this well, the fluid flows into these cracks, and a load is applied to these cracks, resulting in cracks of a size suitable for resource extraction. Although it will grow, by temporarily closing the initially formed cracks with the above-mentioned hydrolyzable resin particles, the subsequent fluid pressurization will make the cracks more effective. It becomes possible to form. Additives added to the fluid to temporarily close the cracks in this way are called diverting agents.

Since the above-mentioned hydrolyzable particles are hydrolyzed and disappear by water or enzymes in the ground, it is not necessary to remove the hydrolyzable particles in a subsequent process, and the well cutting can be efficiently advanced.

By the way, the temperature of the well varies depending on the depth, the temperature inside the well ranges from 40 ° C to 200 ° C, and the optimum hydrolyzable resin differs depending on the temperature inside the well where cracks for resource extraction are formed, especially poly. Oxalate is more hydrolyzable than polylactic acid and is expected to be used in a low temperature range (for example, 80 ° C or lower). It can be used alone, but it can be combined with polylactic acid to increase the rate of hydrolysis of polylactic acid. It also has the function of accelerating.

However, a highly hydrolyzable polymer represented by polyoxalate has a peculiar problem that a problem arises in its workability when it is used by adding it to water. That is, the water resistance to water is low, and the particles are hydrolyzed in a short time, so that they decompose on the ground and cause fusion, or they fully exert the functions required for these particles in the well. It has become difficult.

Further, as described above, when hydrolyzable particles are added to the dispersion liquid for excavation and used, the particle shape and the size of the particles become a problem. That is, since such hydrolyzable particles are introduced into cracks (fractures) formed in the ground and exert functions such as closing the cracks or suppressing the collapse of the cracks. , It is required to have a particle shape close to a spherical shape and to have an appropriate particle size. For example, when the particle shape is indeterminate, which is far from spherical (that is, the roundness of the particle is low), it is difficult to press it into the crack, or even if it can be introduced into the crack, there are many voids. , It becomes difficult to effectively suppress the outflow of gas from the crack. Further, if the particles are too large, it becomes difficult to penetrate into the cracks, and if the particles are too small, it is necessary to use a significantly large amount of particles in order to close the cracks.
However, hydrolyzable particles having a high sphericity and a particle size suitable for hydraulic fracturing have not been known so far.

JP 2014-134090 JP-A-2014-134091 JP-A-2014-177618

Therefore, an object of the present invention is to provide hydrolyzable particles which have hydrolyzability, roundness and particle size suitable for hydraulic fracturing, are easy to handle, and are unlikely to cause fusion between particles. To do.

According to the present invention, hydrolyzable particles having a dispersed structure in which fine particles of a hydrolyzable polymer for adjusting the hydrolyzability of the matrix resin are distributed in the hydrolyzable matrix resin. Provided are hydrolyzable particles characterized in that the average particle size (D ₅₀ ) is in the range of 300 to 1000 μm and the minor axis / major axis ratio has a roundness of 0.8 or more. To.

In the hydrolyzable particles of the present invention,
(1) When the hydrolyzable degree was shown by the weight loss rate when immersed in water at 70 ° C. for 168 hours, the hydrolyzable particles showed a weight retention rate of 50% or less, and the hydrolyzable particles had a weight retention rate of 50% or less. The weight retention rate of the contained matrix resin is 90% or more.
(2) The matrix resin is polylactic acid and the hydrolyzable polymer is polyoxalate.
(3) The polyoxalate is a copolymer having a branched copolymer unit derived from a trifunctional or higher functional alcohol or acid.
Is preferable.

The hydrolyzable particles of the present invention have a dispersed structure in which a polymer for adjusting the hydrolyzability of the matrix is dispersed in a hydrolyzable matrix resin. That is, in these hydrolyzable particles, the polymer for adjusting the hydrolyzability (that is, the easily hydrolyzable polymer) is protected by the matrix resin (that is, the poorly hydrolyzable polymer that exists in the sea). , It is possible to effectively prevent the fusion of particles due to the hydrolysis of the polymer for adjusting the hydrolyzability, and the handling property is excellent.

Further, these hydrolyzable particles have an extremely high roundness represented by a minor axis / major axis ratio of 0.8 or more, and their average particle size (D ₅₀ ) is in the range of 300 to 1000 μm, which is small. It's neither too big nor too big.

Therefore, the hydrolyzable particles of the present invention are extremely useful as an additive added to the dispersion liquid for excavation, particularly as an additive used for closing cracks during hydraulic fracturing.

The figure which shows the schematic structure of an example of the drop-type particle production apparatus used for producing the hydrolyzable particle of this invention. The figure which shows the schematic structure of another example of the drop-type particle production apparatus used for producing the hydrolyzable particle of this invention. An SEM photograph of a film formed from a composition forming hydrolyzable particles produced in the experimental example of the present invention.

<Materials that form hydrolyzable particles>
The hydrolyzable particles of the present invention have a dispersed structure in which a hydrolyzable adjusting polymer for adjusting the hydrolyzability of the matrix resin is distributed in the matrix resin, and such a matrix resin and water are added. As the degradability adjusting polymer, polymers showing various hydrolyzability can be used, but in particular, in addition to appropriate hydrolyzability when used for hydraulic crushing, it is excellent in enzymatic degradability. Therefore, biodegradable polyesters such as polylactic acid, polyhydroxyalkanoate, polyoxalate, polyglycolic acid, polybutylene succinate, polybutylene succinate adipate, and polycaprolactone are suitable. Such biodegradable polyesters can be used alone or in combination of two or more, and further, various aliphatic polyhydric alcohols and aliphatic polybasic acids are used as long as the hydrolyzability is not impaired. , Hydroxycarboxylic acid, lactone and the like can also be used in the form of a copolymer copolymerized.
That is, among the above biodegradable polyesters, those that are difficult to hydrolyze are used as the matrix resin, and those that are more easily hydrolyzable than the matrix resin are used as the polymer for adjusting the hydrolyzability.

Further, it is desirable that the biodegradable polyester has a weight average molecular weight (Mw) in the range of 50,000 to 500,000. Regardless of whether it is applied to a matrix resin or a polymer for adjusting hydrolyzability, if a polymer having an excessively low weight average molecular weight (Mw) is used, the particle strength cannot be maintained in an appropriate range and the particles collapse. This is because it is easy and the particle shape may be difficult to maintain, and if the weight average molecular weight is excessively large, the hydrolyzability is lowered.

By the way, from the viewpoint of being used for mining shale gas, it is desirable that the hydrolyzable resin of the present invention exhibits appropriate hydrolyzability particularly in a low temperature region of 40 to 80 ° C. That is, shale gas is mined from a shale layer existing in a relatively shallow ground, and the excavation dispersion used for the mining is put into a well in the above temperature range. This is because the hydrolyzed particles are required to have appropriate hydrolyzability in this temperature range.

The moderate hydrolyzability as described above is such that the value (weight retention rate) is 60% or less when the hydrolyzability is shown by the weight loss rate when immersed in water at 70 ° C. for 168 hours. It is preferably 50% or less. That is, if the degree of hydrolysis is low and the rate of weight loss is excessively small, when added to a dispersion for hydraulic fracturing described later, even if it can penetrate into cracks, it remains without hydrolysis for a long period of time. Resulting in. In addition, if the degree of hydrolysis is high and the rate of weight loss is excessively large, the particles may collapse due to hydrolysis before they are allowed to enter the cracks, and further, the particles are hydrolyzed on the ground. There is a risk that they will fuse together, making it difficult to supply them into the cracks. Therefore, the weight loss rate measured under the above conditions is preferably in the above range.

1. 1. Matrix resin;
Therefore, in the present invention, it is desired to use a resin having hydrolyzability to the extent that the above-mentioned degree of hydrolysis can be realized as the matrix resin. For this purpose, among the above-mentioned biodegradable polyesters, It is optimal to use the above-mentioned poorly hydrolyzable material having a weight retention rate of 90% or more, for example, polylactic acid as the matrix resin.
That is, if a matrix resin having a high degree of hydrolysis is used, it becomes difficult to adjust the degree of hydrolysis of the target hydrolyzable particles within the above range. Further, using such a resin having a high degree of hydrolysis as a matrix resin is particularly effective in suppressing the hydrolysis of an easily hydrolyzable polymer used as a polymer for adjusting hydrolysis.

The polylactic acid preferably used as a matrix resin may have a molecular weight adjusted to the above-mentioned range so that the degree of hydrolysis thereof is within the above-mentioned range. For example, a homopolymer of D-lactic acid, L-lactic acid, can be used. It may be a homopolymer, or a copolymer of D-lactic acid and L-lactic acid, or in some cases, a copolymer in which other copolymerization components are copolymerized.

2. 2. Polymer for adjusting hydrolyzability;
Further, when the above-mentioned poorly hydrolyzable biodegradable polymer is used as the matrix resin, the hydrolyzable adjusting polymer dispersed in the matrix resin is easily hydrolyzable, and can be blended in a small amount. Polyoxalate and polyglycolic acid are suitable in that the weight retention of the particles can be adjusted within the above range (for example, 50% or less).
Among these, the above-mentioned polyoxalate releases oxalic acid by hydrolysis, and therefore has the property of greatly promoting the hydrolysis of polylactic acid when used in a blend with a substance having low hydrolyzability such as polylactic acid. It is preferable in that the degree of hydrolysis can be adjusted within the above-mentioned range, especially when used in a small amount.
The hydrolyzable adjusting polymer is preferably finely distributed. For example, the average particle size of the dispersed particles is 5 to 0.01 μm, preferably 3 to 0.1 μm, and more preferably 3. It is preferably in the range of ~ 0.5 μm.

For example, the degree of hydrolysis of polyoxalate can be adjusted within the above-mentioned range by using 5 to 95 parts by mass, particularly about 30 to 80 parts by mass, per 100 parts by mass of the above-mentioned polylactic acid. That is, the fact that the degree of hydrolysis can be adjusted with a small amount means that this polyoxalate is coated with a relatively thick layer of polylactic acid, and therefore the polyoxalate is extremely easy to hydrolyze. However, because it is protected by a thick layer of polylactic acid, hydrolysis in an environment near room temperature can be effectively suppressed, and when used as a dispersion for hydraulic crushing, hydrolysis on the ground. It is extremely advantageous in preventing the fusion of particles due to the above.

Further, in the present invention, among the above-mentioned polyoxalates, a polyoxalate copolymer in which a branched structure is introduced into a molecule is particularly preferably used. That is, such a polyoxalate copolymer has a dense molecular structure because a branched structure is introduced into the molecule. For example, a polyoxalate (not yet) in which such a branched structure is not introduced. Compared with (modified copolymer), the hydrolysis rate 12 hours after being dropped in water is extremely low, and the hydrolysis rate 24 hours after being dropped in water is the same as that of unmodified polymer. Equivalent. That is, such a polyoxalate copolymer exhibits hydrolyzability equivalent to that of unmodified polyoxalate, but is significantly lower than that of unmodified polyoxalate in terms of initial hydrolyzability. Presumably, the dense molecular structure significantly suppresses the rate of water permeation, which is believed to lead to a decrease in initial hydrolyzability.

Moreover, the decrease in initial hydrolyzability can effectively avoid sudden hydrolysis due to contact with water or the like when used on the ground, and the fusion of particles to each other due to such hydrolysis can be more reliably performed. It has the advantage of being preventable.
That is, when unmodified polyoxalate is used as a polymer for adjusting hydrolyzability, as described above, the purpose can be achieved with a small amount of use, and it is protected by a thick coating layer of polylactic acid. Although it has the advantage of being able to effectively suppress hydrolysis (initial hydrolysis) when used on the ground, it does not mean that hydrolysis on the ground can be completely prevented because part of it is exposed on the particle surface. Absent. However, the use of the polyoxalate copolymer as described above can effectively suppress the hydrolysis of the polyoxalate copolymer even if a part of the copolymer is exposed on the surface of the particles, and the fusion of the particles during use on the ground can be achieved. It is possible to prevent it even more effectively, and it is possible to greatly improve its operability.

In the present invention, the polyoxalate copolymer into which the above-mentioned branched structure is introduced contains a linearly connected oxalate main ester unit and a branched ester copolymer derived from a trifunctional or higher functional alcohol or acid. The weight average molecular weight (Mw) is in the above-mentioned range, particularly in the range of 5000 to 20000.

In such a polyoxalate copolymer, the oxalate main ester unit linearly connected is represented by the following formula (1):
During the ceremony
n is a positive number,
A is a divalent organic group,
It is represented by.

In such a main ester unit, the divalent organic group A is an organic residue of oxalic acid and an ester-forming dialcohol.
As the oxalic acid diester used for introducing the main ester unit, dialkyl oxalate is preferable, and alkyl groups having 1 to 4 carbon atoms such as dimethyl oxalate, diethyl oxalate, and propyl oxalate are preferable. Most preferably, dimethyl oxalate and diethyl oxalate are used from the viewpoint of transesterification and the like.
The dialcohols used to introduce the main ester unit include ethylene glycol, 1,3 propanediol, propylene glycol, butanediol, hexanediol, octanediol, dodecanediol, neopentyl glycol, bisphenol A, and cyclohexanedimethanol. Etc. can be exemplified. Among these, aliphatic dialcohols, particularly linear dihydric alcohols, are preferable because they have excellent long-term hydrolyzability and have little impact on the environment. For example, ethylene glycol, propylene glycol, butanediol, hexanediol, and octanediol are preferable. , Dodecanediol. In particular, butanediol is most suitable from the viewpoint of having a high effect of suppressing the initial hydrolyzability by introducing the branched ester copolymerization unit.
Further, in the main ester unit, a dicarboxylic acid having an aliphatic ring or an aromatic ring is contained in an amount of 20 mol% or less, particularly 5 mol% or less, per oxalic acid within a range in which the desired hydrolyzability is not impaired. Acids (eg cyclohexanedicarboxylic acid, phthalic acid, etc.) may be copolymerized.

The branched ester copolymerization unit is, for example, the following formula (2) or (3):
P- (O-CO-CO) -r (2)
Q- (OAO) -r (3)
In the above formula,
P is a residue of a trifunctional or higher functional alcohol used to introduce a branched ester copolymerization unit.
Q is a trifunctional or higher acid residue used to introduce the branched ester copolymerization unit.
A represents a divalent organic group as in the above formula (1).
r is the valence of a trifunctional or higher functional alcohol or acid,
It is represented by.
That is, since such a branched copolymer unit is introduced into the linear main ester unit to form a branched structure, this polyoxalate copolymer can be used for a long period of time while the initial hydrolyzability is suppressed. The hydrolyzability is maintained at a high level.

In the above-mentioned branched ester copolymerization unit (hereinafter, may be simply referred to as a branched unit), a residue of a trifunctional or higher alcohol (P in the formula (2)) and a residue of a trifunctional or higher acid. It is desirable that the number of carbon atoms in (Q) in the formula (3) is 18 or less. This is because when these residues P and Q are long chains, the effect of reducing the initial hydrolyzability due to the branched structure is diminished.

Examples of the trifunctional or higher-functional alcohol having a residue having the above-mentioned carbon number include triols such as glycerin, trimethylolmethane, trimethylolethane and trimethylolpropane, and tetraol such as tetramethylolmethane (pentaerythritol). Examples thereof include polyfunctional aliphatic alcohols represented by the above, and examples of trifunctional or higher functional acids include aliphatic tricarboxylic acids such as propanetricarboxylic acid and cyclohexanetricarboxylic acid, and aliphatic tetracarboxylic acids such as ethylenetetracarboxylic acid. , Aromatic tricarboxylic acids such as trimellitic acid, aromatic tetracarboxylic acids such as benzenetetracarboxylic acid, biphenyltetracarboxylic acid and benzophenonetetracarboxylic acid, and acid anhydrides thereof.

In the present invention, it is preferable that the branched ester copolymerization unit is introduced by a trifunctional or higher functional alcohol, for example, linear ester copolymerization by pentaerythritol, from the viewpoint of not impairing the long-term hydrolyzability. It is preferable that the unit is introduced.

The above-mentioned branched units are preferably introduced in an amount of 0.01 to 1.0 mol% per main ester unit that is linearly connected. That is, if the amount of the branched ester copolymerization unit is small, the effect of reducing the initial hydrolyzable property is small, and if a large amount of the branched unit is introduced more than necessary, the branched unit is connected to the branched unit. The molecular weight of the linear main ester unit becomes small, and as a result, the effect of reducing the initial hydrolysis characteristics due to the branched structure becomes low, and the solvent-insoluble content (gel fraction) contained in the particles increases, resulting in molding. The properties are greatly reduced, and for example, it may be difficult to form granules.

The polyoxalate copolymer in which the above-mentioned branched structure is introduced has a oxalic acid source (oxalic acid or oxalic acid ester) for forming a linear main ester unit, a dihydric alcohol component, and branched unit formation. It is produced by carrying out a polycondensation reaction by a known method so that branched units are formed at the above-mentioned ratios using a polyhydric alcohol component or a polybasic acid component for use and a catalyst.
Here, as the catalyst, compounds such as P, Ti, Ge, Zn, Fe, Sn, Mn, Co, Zr, V, Ir, La, Ce, Li, Ca, and Hf are typical, and in particular, organic titanium. Compounds and organotin compounds are preferable, and for example, titanium alkoxide, dibutyltin dilaurate, butyltin hydroxydooxide hydride and the like are preferable because of their high activity.
In the polycondensation reaction, a heat resistant agent may be added if necessary to prevent thermal deterioration. Further, a catalytically active deactivator may be added when stopping the polymerization.

After synthesizing the above-mentioned polyoxalate composed of the linear main ester unit, a polycondensation reaction or a transesterification reaction is carried out by adding a polyfunctional alcohol or a polybasic acid component for the branched unit in a subsequent step. , The desired polyoxalate copolymer of the present invention can also be produced.
In this subsequent step, the polyfunctional component can be introduced by adding a trifunctional or higher functional component to the melt and mixing the linear polyoxalate by using an extruder.

In the polyoxalate copolymer obtained as described above, the above-mentioned branched unit is introduced as the copolymer ester unit, but the solvent-insoluble component measured with dichloromethane at 23 ° C. (by adjusting the introduction amount) The gel fraction) is in the range of 1% by mass or more and 70% by mass or less, which is advantageous in reducing the initial hydrolysis characteristics. It is preferably 10% or more and 70% or less, and more preferably 30% or more and 70% or less. As described above, when the amount of the branched unit introduced is small and the solvent insoluble content is smaller than the above range, or when the amount of the branched unit introduced is large and the solvent insoluble content is larger than the above range. In any of these cases, the effect of reducing the initial hydrolysis characteristics is reduced.

3. 3. Other combinations;
In addition to the matrix resin and the polymer for adjusting hydrolyzability as described above, the hydrolyzable particles of the present invention include known plasticizers, heat stabilizers, light stabilizers, antioxidants, as required. Contains additives such as UV absorbers, flame retardants, colorants, pigments, fillers, fillers, mold release agents, antistatic agents, fragrances, lubricants, foaming agents, antibacterial / antifungal agents, and nucleating agents. May be good.

<Form of hydrolyzable particles>
As described above, the hydrolyzable particles of the present invention use a poorly hydrolyzable resin such as polylactic acid as a matrix, and a hydrolyzable adjusting polymer such as polyoxalate is dispersed in the matrix resin. Although it has a structure, it has a high sphericity, and for example, the roundness represented by the minor axis / major axis ratio is 0.8 or more, and particularly very close to 1.
_{Further, the particles have an average particle size (D 50} ) on a volume basis measured by a laser diffraction / scattering method in the range of 300 to 1000 μm.

That is, the hydrolyzable particles of the present invention have high sphericity as described above, and at the same time, the size of the particles is suitable for introduction into cracks formed in the well during hydraulic fracturing. It has a size. For this reason, it exhibits excellent functions as an agent called a diverting agent that is introduced into cracks formed in a well during hydraulic fracturing and temporarily closes the cracks.
For example, if the sphericity is lower than the above range, even if it can be introduced into the crack, the function of closing the crack is poor, the outflow of gas from the crack cannot be effectively suppressed, and the crack is further cracked by the fluid pressure. It interferes with the work of forming. Further, if the particle size is larger than the above range, it becomes difficult to introduce the particles into the crack, and if the particle size is smaller than the above range, it becomes difficult to effectively close the crack. Furthermore, when handling the product, problems such as dust scattering are likely to occur.

As described above, the hydrolyzable particles of the present invention have a form suitable for use by adding to a dispersion liquid for excavation for hydraulic fracturing at the time of hydraulic fracturing. In comparison, the angle of repose is extremely small, 50 degrees or less (see Examples described later for the measurement method).

<Manufacturing of hydrolyzable particles>
By the way, the hydrolyzable particles having a high sphericity and an appropriate particle size as described above are produced by a dropping method using a dropping nozzle having a single tube structure or a multi-tube structure, and other methods. Then, it is difficult to manufacture.
For example, in mechanical grinding using a resin composition (a mixture containing a matrix resin, a polymer for adjusting hydrolyzability, and an appropriately blended compounding agent) that forms hydrolyzable particles, it is natural that the particles are true. The degree of sphericalness becomes low.
Further, as a method for producing spherical particles, a method using a poor solvent or a method such as spray spraying makes the particle size too fine, and further, even if the strand is cut by extruding the resin, the particle size becomes large. It becomes extremely coarse.
As described above, in the method generally adopted conventionally, even if the particle size can be formed into a spherical shape, the particle size cannot be adjusted within the above-mentioned range (300 to 1000 μm).

The hydrolyzable particles of the present invention are produced by using a dropping method using a dropping nozzle, and the dropping type particle manufacturing apparatus used in such a dropping method is a single tube as shown in FIG. There is a structure and a multi-tube structure as shown in FIG.

In the single-tube structure of FIG. 1, the liquid A is supplied to the nozzle of the single-tube indicated by 5, and the droplet 7 of the liquid A is dropped from the tip thereof, and the receiving tank 9 keeps the droplet state. Dropped into.

As the above-mentioned liquid A, a liquid of the resin composition (a mixture containing a matrix resin, a polymer for adjusting hydrolyzability, and a compounding agent appropriately blended) that forms the above-mentioned hydrolyzable particles is used. As such a solution of hydrolyzable particles (solution A), it is possible to directly supply the melt prepared by melting and mixing each component to the single tube nozzle 5, but since it has a high viscosity, it is predetermined. Since it is difficult to adjust the flow rate for dropping the droplet 7 adjusted to the particle size of the above, the viscosity is adjusted to about 10 to 10000 mPa · sec (25 ° C.) using a predetermined organic solvent, and this hydrolysis is performed. It is preferable to supply the organic solvent solution of the sex particles as the solution A.
Examples of the organic solvent used here include dichloromethane, chloroform, dimethyl sulfoxide, dimethylformamide, acetone, toluene, ethyl acetate and the like. The concentration is preferably in the range of 10% to 70%.

The droplets dropped from the tip of the single tube nozzle 5 as described above are dropped into the receiving tank 9. The receiving tank 9 is filled with a poor solvent for hydrolyzable particles such as water and methanol, and is precipitated and solidified in this place to obtain hydrolyzable particles 11 having a desired particle size.

Further, in the multi-tube structure of FIG. 2, the dropping nozzle 5 is formed of the core tube 1 and the outer tube 3, and the droplet 7 dropped from the nozzle 5 is the receiving tank 9 as described above. Dropped into.

That is, in this device, the liquid A is supplied to the core tube 1 of the dropping nozzle 5, and the liquid B is supplied to the outer tube 3. Therefore, the droplet 7 dropped from the nozzle 5 has the liquid A as the core. , Has a capsule structure with liquid B as a shell.

In the present invention, as the liquid A forming the core of the droplet 7, the liquid of the resin composition for forming the hydrolyzable particles described above is used as in the case of FIG. 1, and the liquid B forming the shell of the droplet 7 is used. As the liquid, an aqueous solution of sodium alginate is used. That is, this liquid B functions as a particle size adjusting agent that prevents fusion of the resin composition that forms hydrolyzable particles and maintains a constant particle size.

The above-mentioned solution A (the solution of the resin composition for forming hydrolyzable particles) is prepared by melting and mixing each component, and this melt can be directly supplied as the solution A, but the viscosity is high. Therefore, it is difficult to adjust the flow rate for dropping the droplets 7 so that the droplets 7 having a predetermined particle size are formed. Therefore, the viscosity is 10 to 1000 mPa · using the same volatile organic solvent as described above. It is preferable to adjust the temperature to about sec (25 ° C.) and supply this solution as the solution A.

By supplying such a liquid A to the core tube 1, supplying the above sodium alginate aqueous solution as the liquid B and dropping the liquid A, a droplet 7 encapsulated with the liquid A as the core and the liquid B as the shell is formed. However, in this case, in order to effectively perform encapsulation, it is desirable that the viscosity of the sodium alginate aqueous solution used as the liquid B is adjusted to about 10 to 1000 mPa · sec (25 ° C.). For example, the concentration of the aqueous solution is preferably in the range of about 1 to 5% by mass.
Further, the inner diameter of the tip of the nozzle 5 (inner diameter of the core tube 1 and the outer tube 3) as described above is set within a range in which the diameter of the particles finally obtained is within the above-mentioned range, and the liquid A and the liquid A and The supply speed of the liquid B is also set to be in an appropriate range, but it is usually desirable that the flow rate ratio of the liquid A to the liquid B is set appropriately.

The droplet 7 dropped from the tip of the nozzle 5 as described above is dropped into the receiving tank 9.
The receiving tank 9 is filled with an aqueous solution of calcium chloride, whereby droplets 10 of hydrolyzable particles covered with calcium alginate are deposited. By immersing the droplet 10 thus precipitated in the sodium citrate aqueous solution stretched in the receiving tank 9', the particles 11 in which the shell of the liquid B is removed from the droplet 10 can be obtained.

The polyoxalate particles 11 obtained by using the dropping nozzles of FIGS. 1 and 2 are all immediately recovered from the receiving tank 9 or 9', and if they contain a solvent, they are appropriately added to water to add the solvent. Remove. This operation may be performed before removing the coating sodium alginate when encapsulation is performed using the apparatus of FIG.
Further, in general, the obtained particles are appropriately sieved to collect particles having a predetermined particle size, and further appropriately dried with hot air to be used as the target hydrolyzable particles. ..

In the above description, an example in which an aqueous solution of sodium alginate is used as the solution B forming the shell is shown, but of course, the present invention is not limited to this, and the periphery of the droplet of the solution A is stably covered. , An aqueous solution of salts or the like having an appropriate viscosity that can prevent fusion between solutions A can be used as solution B. Further, depending on the type of the liquid B, the type of the aqueous solution to be applied to the receiving tank 9 can be appropriately selected.

<Use>
Since the hydrolyzable particles of the present invention can effectively avoid inconveniences such as dust scattering and effectively prevent fusion on the ground, they are easy to handle and are formed at the time of hydraulic fracturing. It has the function of introducing into cracks and temporarily closing the cracks, and after a certain period of time, it hydrolyzes and disappears.
Therefore, it is suitably used for the preparation of excavation dispersions such as fracturing fluids used at the mining site of underground resources, and especially for shale gas mining, it is used as an aqueous liquid using water as a medium together with propant such as sand grains. It is added and is preferably used as a fracturing fluid.

<Melting point measurement>
Equipment: DSC6220 manufactured by Seiko Instruments Inc. (differential scanning calorimetry)
Sample preparation: Sample amount 5-10 mg
Measurement conditions: Measured in the range of 0 ° C to 250 ° C at a heating rate of 10 ° C / min under a nitrogen atmosphere. The melting point was determined at the peak.

<Measurement of molecular weight>
Equipment: Gel Permeation Chromatograph GPC
Detector: Differential refractometer RI
Column: Shodex HFIP-LG (1), HFIP-806M (2) (Showa Denko)
Solvent: Hexafluoroisopropanol (added 5 mM sodium trifluoroacetate)
Flow velocity: 0.5 mL / min
Column temperature: 40 ° C
Sample preparation:
5 mL of the solvent was added to about 1.5 mg of the sample, and the mixture was gently stirred at room temperature (sample concentration 0.03%). After visually confirming that it was dissolved, it was filtered through a 0.45 μm filter. All samples were measured within about 1 hour from the start of preparation. Polymethylmethacrylate was used as the standard.

<Polymerization of PEOx>
In a 1 L separable flask equipped with a mantle heater, a liquid temperature thermometer, a stirrer, a nitrogen introduction tube, and a distillation column,
Dimethyl oxalate 472 g (4 mol)
Ethylene glycol 297g (4.8mol)
Tetrabutyl titanate 0.40g
Was put in, and the liquid temperature in the flask was heated to 120 ° C. under a nitrogen air flow, and atmospheric pressure polymerization was carried out.
After the distillation of methanol was started, the liquid temperature was gradually raised to 200 ° C. and polymerization under normal pressure was carried out to finally obtain 260 ml of a distillate.
Then, the liquid temperature in the flask was 200 ° C., and the vacuum polymerization was carried out at a reduced pressure of 0.1 kPa to 0.8 kPa. The obtained polymer was taken out, granulated by a crusher, and vacuum heat-treated at 120 ° C. for 2 hours to crystallize.
The obtained polymer (PEOx) had a melting point of 180 ° C. and a weight average molecular weight of 70,000.

<Example 1>
0.95 g of polylactic acid, 0.05 g of PEOx, and 15 ml of HFIP solvent were added to a 20 ml vial and dissolved so that the content of PEOx was 5 wt%. After melting, it was cast on a Teflon petri dish to prepare a film.
The obtained film was immersed in water at 37 ° C. for 2 days to hydrolyze PEOx on the surface. The film was observed by SEM (Fig. 1).
The black part in FIG. 1 is a space formed by removing PEOx, and it was confirmed that PEOx particles having an average particle size of 2 μm were distributed in the polylactic acid matrix resin.

1: Core tube 3: Outer tube 5: Drop nozzle 7: Drop 9: Receiving tank

Claims (3)

Hydrolyzable particles having a dispersed structure in which fine particles of a hydrolyzable polymer for adjusting the hydrolyzability of the matrix resin are distributed in the hydrolyzable matrix resin, and have an average particle size. (D ₅₀ ) is in the range of 300 to 1000 μm, has a minor axis / major axis ratio of 0.8 or more, and has a roundness.
A hydrolyzable adjusting polymer having a higher hydrolyzability than the matrix resin is used for the fine particles.
Hydrolyzable particles, wherein the hydrolyzable adjusting polymer is a polyoxalate copolymer in which a branched structure is introduced at a ratio of 0.01 to 1.0 mol% per main ester unit. The hydrolyzable particles according to claim 1, wherein the matrix resin is polylactic acid and the hydrolyzable polymer is polyoxalate. The hydrolyzable particle according to claim 2, wherein the polyoxalate is a copolymer having a branched copolymer unit derived from a trifunctional or higher functional alcohol or acid.