JP2016147971A - Hydrolyzable particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide hydrolyzable particles which have hydrolyzability, circularity and a particle size that are suitable for hydraulic fracturing, are easy to be handled, and hardly cause fusion between particles.SOLUTION: Hydrolyzable particles have such a dispersed structure that fine particles of a hydrolyzable polymer for adjusting hydrolyzability of a hydrolyzable matrix resin are distributed in the matrix resin, and have such circularity that an average particle diameter (D) is in a range of 300-1,000 μm and a ratio of minor axis/major axis is 0.8 or more.SELECTED DRAWING: None

Description

  The present invention relates to a hydrolysable particle, and more particularly to a hydrolysable particle suitably used as an additive to be added to a drilling dispersion.

Hydrolyzable resins typified by polyoxalate and polylactic acid are also excellent in biodegradability. From the viewpoint of environmental improvement, etc., they are currently being investigated as substitutes for various plastics in various applications. Has been put to practical use.
Recently, the use as an additive to be added to the drilling fluid used when collecting underground resources has also been proposed (see Patent Documents 1 to 3).

  For example, a well drilling method called a hydraulic fracturing method is currently widely used for collecting underground resources. Such a drilling method pressurizes the drilling fluid filling the well at high pressure, thereby generating a crack (fracture) in the vicinity of the well, improving the permeability (ease of fluid flow) in the vicinity of the well, It expands the effective cross section of resources such as oil and gas into the well, and increases the productivity of the well. Such drilling fluids are also called fracturing fluids. In the past, viscous fluids such as gel-like gasoline were used, but recently, shale gas produced from a shale layer that exists in a relatively shallow place. With the development of the above, considering the influence on the environment, aqueous dispersions in which polymer particles are dissolved or dispersed in water have been used. As such polymers, hydrolyzable resins such as polyoxalate and polylactic acid have been proposed.

That is, when the drilling fluid in which the hydrolyzable particles as described above are dispersed in water is filled in the well and is pressurized, the particles penetrate into the vicinity of the well, and cracks (fractures) that have already formed are formed. ) As a sealing material (sealing material), and the passage of resources such as gas and oil can be effectively blocked temporarily.
In general, in order to generate a crack in a well, a preliminary blast called perporation is performed in a horizontal well. Such preliminary blasting produces a large number of small cracks along with relatively large cracks in the deep part of the well. After that, when a drilling fluid (fracturing fluid) is injected into the well, the fluid flows into these cracks, and a load is applied to these cracks, so that the cracks have a size suitable for collecting resources. Although it will grow, the crack formed at the beginning is temporarily clogged with the above-mentioned hydrolyzable resin particles, so that the subsequent fluid pressurization makes the crack more effective. It becomes possible to form. The additive added to the fluid in order to temporarily close the crack in this way is called a diverting agent.

  Since the hydrolyzable particles are hydrolyzed by underground water and enzymes and disappear, it is not necessary to remove the hydrolyzable particles in a subsequent process, and the well drilling is efficiently advanced.

  By the way, the temperature of the well varies depending on the depth, the temperature in the well varies widely from 40 ° C to 200 ° C, and the optimum hydrolyzable resin varies depending on the temperature in the well where the crack for resource collection is formed. Oxalate is highly hydrolyzable compared to polylactic acid and is expected to be used in a low temperature range (for example, 80 ° C. or less). It also has the function of accelerating.

  However, a highly hydrolyzable polymer typified by polyoxalate has a specific problem that when it is used by adding it to water, there is a problem in workability. That is, the water resistance is low, and the particles hydrolyze in a short time, so that they decompose on the ground and cause fusion, or sufficiently perform the functions required for the particles in the well. It has become difficult.

Furthermore, as described above, when hydrolyzable particles are added to the excavation dispersion, the shape and size of the particles are problematic. That is, such hydrolysable particles are introduced into cracks (fractures) formed in the ground, and serve to close the cracks or to suppress the collapse of the cracks. Therefore, it is required to have a particle shape close to a spherical shape and an appropriate particle size. For example, if the particle shape is indefinitely far from a sphere (ie, the roundness of the particle is low), there are many voids even if it is difficult to press-fit into the crack or it can be introduced into the crack. It becomes difficult to effectively suppress the outflow of gas from the crack. If the particles are too large, it is difficult to penetrate into the cracks. If the particles are too small, it is necessary to use a remarkably large amount of particles in order to close the cracks.
However, hydrolysable particles having a high sphericity and a particle size suitable for hydraulic fracturing have not been known so far.

JP2014-134090A JP2014-134091A JP2014-177618A

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

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

In the hydrolyzable particles of the present invention,
(1) When the hydrolyzability is shown by the weight loss rate when immersed in water at 70 ° C. for 168 hours, the hydrolyzable particles show a weight retention of 50% or less, and the hydrolyzable particles The weight retention of the matrix resin contained 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 tri- or higher functional alcohol or acid,
Is preferred.

  The hydrolyzable particles of the present invention have a dispersion structure in which a polymer for adjusting the hydrolyzability of the matrix is dispersed in a hydrolyzable matrix resin. That is, in this hydrolysable particle, the polymer for adjusting hydrolyzability (that is, the easily hydrolyzable polymer) is protected by the matrix resin (that is, the hardly hydrolyzable polymer existing in the sea state). Further, it is possible to effectively prevent the fusion of particles due to hydrolysis of the hydrolyzability adjusting polymer, and the handling property is excellent.

In addition, the hydrolyzable particles have an extremely high roundness represented by the ratio of short diameter / major diameter of 0.8 or more, and the average particle diameter (D ₅₀ ) is in the range of 300 to 1000 μm, which is small. It ’s never too big, it ’s not too big.

  Accordingly, the hydrolyzable particles of the present invention are extremely useful as an additive added to the dispersion for excavation, particularly as an additive used for clogging cracks during hydraulic crushing.

The figure which shows schematic structure of an example of the dripping type particle manufacturing apparatus used for manufacture of the hydrolysable particle | grains of this invention. The figure which shows schematic structure of the other example of the dripping type particle manufacturing apparatus used for manufacture of the hydrolysable particle | grains of this invention. The SEM photograph of the film formed from the composition which forms the hydrolysable particle produced in the experiment example of this invention.

<Material for forming hydrolyzable particles>
The hydrolyzable particles of the present invention have a dispersion structure in which a polymer for adjusting hydrolyzability for adjusting the hydrolyzability of the matrix resin is distributed in the matrix resin. As the polymer for adjusting degradability, any polymer exhibiting various hydrolyzability can be used. In particular, in addition to moderate hydrolyzability when used for hydraulic crushing, it is excellent in enzyme degradability. Therefore, biodegradable polyesters such as polylactic acid, polyhydroxyalkanoate, polyoxalate, polyglycolic acid, polybutylene succinate, polybutylene succinate adipate, and polycaprolactone are preferable. Such biodegradable polyesters can be used alone or in combination of two or more, and various aliphatic polyhydric alcohols and aliphatic polybasic acids are used as long as the hydrolyzability is not impaired. , Hydroxycarboxylic acid, lactone and the like may be used in the form of a copolymer.
That is, among the biodegradable polyesters, those that are hardly hydrolysable are used as the matrix resin, and those that are more easily hydrolysable than the matrix resin are used as the hydrolyzable adjusting polymer.

  The biodegradable polyester preferably has a weight average molecular weight (Mw) in the range of 50,000 to 500,000. When applied to either a matrix resin or a hydrolyzable polymer, if the weight average molecular weight (Mw) is too low, the particle strength cannot be maintained in an appropriate range and disintegrated. This is because it is easy to maintain the particle shape, and those having an excessively high weight average molecular weight result in a decrease in hydrolyzability.

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

  The moderate hydrolyzability as described above is 60% or less when the hydrolyzability is indicated by the weight reduction rate when immersed in water at 70 ° C. for 168 hours, Preferably it is 50% or less. That is, if the degree of hydrolysis is low and the weight loss rate is too small, it remains without hydrolysis for a long time even if it can penetrate into the crack when added to the dispersion for hydraulic fracturing described later. Resulting in. Also, if the degree of hydrolysis is high and the weight loss rate is excessively large, for example, the particles may collapse by hydrolysis before entering into the cracks. There exists a possibility that the fusion | melting will be produced and supply to a crack may become difficult. Therefore, the weight loss rate measured under the above conditions is preferably in the above range.

1. Matrix resin;
Accordingly, in the present invention, it is desired to use a resin having hydrolyzability to such an extent that the degree of hydrolysis as described above can be used as a matrix resin. For this purpose, among the biodegradable polyesters described above, It is optimal to use a non-hydrolyzable material having a weight retention of 90% or more, such as polylactic acid, as the matrix resin.
That is, if a matrix resin having a high degree of hydrolysis is used, it is difficult to adjust the degree of hydrolysis of the target hydrolyzable particles to the above range. In addition, the use of such a highly hydrolyzed resin as a matrix resin is particularly effective in terms of suppressing hydrolysis of a readily hydrolyzable polymer used as a hydrolysis adjusting polymer.

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

2. Hydrolyzable adjusting polymer;
Furthermore, when a hardly hydrolyzable biodegradable polymer as described above is used as a matrix resin, the hydrolyzable adjusting polymer dispersed in this matrix resin is easily hydrolyzable, and in a small amount, Polyoxalate and polyglycolic acid are preferable in that the weight retention of the particles can be adjusted to the above-described range (for example, 50% or less).
Among these, the above-mentioned polyoxalate releases oxalic acid by hydrolysis, so when used in a blend with low hydrolyzable materials such as polylactic acid, it has the property of greatly promoting the hydrolysis of polylactic acid. It is preferable in that the degree of hydrolysis can be adjusted to the above-described range by using a small amount.
Further, the polymer for adjusting hydrolyzability is preferably finely distributed. For example, the average particle diameter of the dispersed particles is 5 to 0.01 μm, preferably 3 to 0.1 μm, more preferably 3 It is good to be in the range of ˜0.5 μm.

  For example, polyoxalate can adjust a hydrolysis degree to the range mentioned above by use of 5-95 mass parts per 100 mass parts of polylactic acid mentioned above, especially about 30-80 mass parts. That is, the ability to adjust the degree of hydrolysis with a small amount means that the polyoxalate is coated with a relatively thick polylactic acid layer, and therefore the polyoxalate is very easily hydrolyzed. However, because it is protected by a thick layer of polylactic acid, it can effectively suppress hydrolysis in an environment near room temperature. Hydrolysis on the ground when used as a dispersion for hydraulic fracturing This is extremely advantageous in preventing the fusion of particles due to the above.

  In the present invention, among the polyoxalates described above, polyoxalate copolymers having a branched structure introduced in the molecule are 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 having no such branched structure introduced (not yet) Compared with the modified polyoxalate), the hydrolysis rate after 12 hours from dropping in water is extremely low, and the hydrolysis rate after 24 hours from dropping in water is the same as that of unmodified polyoxalate. It is equivalent. That is, such a polyoxalate copolymer exhibits hydrolyzability equivalent to that of unmodified polyoxalate, but is significantly lower than unmodified polyoxalate in terms of initial hydrolyzability. Presumably, due to the dense molecular structure, the water penetration rate is remarkably suppressed, which leads to a decrease in initial hydrolyzability.

Moreover, the decrease in initial hydrolyzability can effectively avoid sudden hydrolysis due to contact with moisture, etc. when used on the ground, and the fusion of particles due to such hydrolysis can be more reliably performed. The advantage is that it can be prevented.
That is, when the 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 with a thick coating layer of polylactic acid. Although there is an advantage that hydrolysis (initial hydrolysis) at the time of use on the ground can be effectively suppressed, a part of it is exposed to the particle surface, so that hydrolysis on the ground cannot be completely prevented. Absent. However, the use of the polyoxalate copolymer as described above can effectively suppress the hydrolysis even when a part of the polyoxalate copolymer is exposed on the particle surface, thereby preventing the fusion of the particles when used on the ground. This can be prevented more effectively, and the operability can be greatly improved.

  In the present invention, the polyoxalate copolymer into which the above-described branched structure is introduced includes a linear oxalate main ester unit and a branched ester copolymer unit derived from a tri- or higher functional alcohol or acid. The weight average molecular weight (Mw) is in the above-described range, and particularly in the range of 5000 to 200000.

In such a polyoxalate copolymer, the oxalate main ester unit connected in a straight chain is represented by the following formula (1):
Where
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 a dialcohol that can form an ester with oxalic acid.
As the oxalic acid diester used for introducing the main ester unit, dialkyl oxalate is preferable, and an alkyl group having 1 to 4 carbon atoms such as dimethyl oxalate, diethyl oxalate, and propyl oxalate is preferable. Most preferred are dimethyl oxalate and diethyl oxalate from the viewpoint of transesterification and the like.
The dialcohol used to introduce the main ester unit is ethylene glycol, 1,3 propanediol, propylene glycol, butanediol, hexanediol, octanediol, dodecanediol, neopentyl glycol, bisphenol A, cyclohexanedimethanol. Etc. can be illustrated. Among these, fatty dialcohols, particularly straight chain dihydric alcohols, are preferred because they have excellent long-term hydrolyzability and little influence on the environment. For example, ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol , Dodecanediol. In particular, butanediol is optimal from the viewpoint that the effect of suppressing the initial hydrolyzability by the introduction of the branched ester copolymer unit is high.
Further, in the main ester unit, a dicarboxylic acid having an aliphatic ring or an aromatic ring in an amount not exceeding the target hydrolyzability, for example, 20 mol% or less, particularly 5 mol% or less per oxalic acid. An acid (for example, cyclohexanedicarboxylic acid or phthalic acid) may be copolymerized.

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

  In the above-mentioned branched ester copolymer unit (hereinafter, sometimes simply referred to as a branched unit), a residue of trifunctional or higher alcohol (P in formula (2)) and a residue of trifunctional or higher acid The number of carbon atoms in (Q in Formula (3)) is preferably 18 or less. This is because when these residues P and Q are long chains, the effect of lowering the initial hydrolyzability due to the branched structure becomes dilute.

  Examples of the tri- or higher functional alcohol having a residue having a carbon number as described above include triols such as glycerin, trimethylolmethane, trimethylolethane, and trimethylolpropane, and tetraols such as tetramethylolmethane (pentaerythritol). The polyfunctional aliphatic alcohol represented by the above can be exemplified, and the trifunctional or higher acid includes aliphatic tricarboxylic acids such as propanetricarboxylic acid and cyclohexanetricarboxylic acid, and aliphatic tetracarboxylic acids such as ethylenetetracarboxylic acid. And 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, from the viewpoint of not impairing the long-term hydrolyzability, it is preferable that a branched ester copolymer unit is introduced with a trifunctional or higher alcohol, for example, a linear ester copolymer with pentaerythritol. Preferably, units are introduced.

  The above-mentioned branched unit is preferably introduced in an amount of 0.01 to 1.0 mol% per main ester unit continuous in a straight chain. That is, when the amount of the branched ester copolymer unit is small, the effect of reducing the initial hydrolyzability is reduced, and when the branched unit is introduced in a larger amount than necessary, the branched unit is connected to the branched unit. As a result, the molecular weight of the linear main ester unit is reduced. As a result, the effect of reducing the initial hydrolysis characteristics due to the branched structure is reduced, and the solvent-insoluble content (gel fraction) contained in the particles is increased. For example, there is a possibility that molding may be difficult.

The polyoxalate copolymer having the branched structure as described above is composed of an oxalic acid source (oxalic acid or oxalic acid ester) for forming a linear main ester unit, a dihydric alcohol component, and a branched unit formation. The polycondensation reaction is carried out by a known method using a polyhydric alcohol component or polybasic acid component for use and a catalyst so that the branched units are formed at the aforementioned ratio.
Here, typical examples of the catalyst include compounds such as P, Ti, Ge, Zn, Fe, Sn, Mn, Co, Zr, V, Ir, La, Ce, Li, Ca, and Hf. Compounds and organic tin compounds are preferred, and for example, titanium alkoxide, dibutyltin dilaurate, butyltin hydroxide oxide hydrate 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 degradation. Further, a catalyst deactivator may be added when the polymerization is stopped.

After synthesizing the polyoxalate composed of the above-mentioned linear main ester unit, a polyfunctional alcohol or polybasic acid component for the branched unit is added in the subsequent step, and a polycondensation reaction or a transesterification reaction is performed. The intended polyoxalate copolymer of the present invention can also be produced.
In this post-process, the polyfunctional component can also be introduced by adding a trifunctional or higher polyfunctional component and melting and mixing it while melting the linear polyoxalate using an extruder.

  In the polyoxalate copolymer obtained as described above, the above-mentioned branched unit is introduced as a copolymerized ester unit. By adjusting the amount of the introduced unit, a solvent-insoluble content (measured in dichloromethane at 23 ° C.) It is advantageous for reducing the initial hydrolysis characteristics that the gel fraction) is in the range of 1% by mass to 70% by mass. Preferably they are 10% or more and 70% or less, More preferably, they are 30% or more and 70% or less. As mentioned above, when the amount of branched units introduced is small and the solvent insoluble content is smaller than the above range, and when the amount of branched units introduced is large and the solvent insoluble content is larger than the above range. In either case, the effect of reducing the initial hydrolysis characteristics becomes small.

3. Other compounding agents;
In addition to the matrix resin and the polymer for adjusting hydrolyzability, the hydrolyzable particles of the present invention include, as necessary, known plasticizers, heat stabilizers, light stabilizers, antioxidants, Additives such as UV absorbers, flame retardants, colorants, pigments, fillers, fillers, mold release agents, antistatic agents, fragrances, lubricants, foaming agents, antibacterial / antifungal agents, nucleating agents, etc. Also good.

<Form of hydrolyzable particles>
As described above, the hydrolyzable particles of the present invention have a matrix in which a hardly hydrolyzable resin such as polylactic acid is used, and a hydrolyzable adjustment 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 ratio of the minor axis / major axis is 0.8 or more, particularly extremely close to 1.
Also, the particles have an average particle size based on volume measured by a laser diffraction scattering method _{(D 50)} is in the range of 300 to 1000.

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 wells during hydraulic fracturing. It has a size. For this reason, it exhibits an excellent function as an agent called a diverting agent that is introduced into a crack formed in a well during hydraulic fracturing and temporarily closes the crack.
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, and the outflow of gas from the crack cannot be effectively suppressed. It will interfere with the work to be formed. If the particle size is larger than the above range, it is difficult to introduce particles into the crack, and if the particle size is smaller than the above range, it is difficult to effectively block the crack. In addition, problems such as dust scattering are likely to occur during handling.

  As described above, the hydrolyzable particles of the present invention have a form suitable for use in addition to a dispersion for excavation for hydraulic fracturing during hydraulic fracturing. In comparison, the angle of repose is as small as 50 degrees or less (refer to Examples described later for the measurement method).

<Manufacture 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 multiple tube structure, and other methods. Then, manufacturing is difficult.
For example, in mechanical pulverization using a resin composition that forms hydrolyzable particles (a mixture containing a matrix resin, a hydrolyzability adjusting polymer, and a compounding agent that is blended as appropriate), it is natural that The sphericity becomes low.
In addition, as a method for producing spherical particles, a method using a poor solvent or a method such as spray spraying causes the particle size to become too fine, and even in strand cutting by resin extrusion, the particle size is too small. It becomes extremely coarse.
As described above, in the methods generally employed in the past, even if the particle diameter can be formed into a true sphere, the particle diameter cannot be adjusted to the above-described range (300 to 1000 μm).

  The hydrolyzable particles of the present invention are manufactured using a dropping method using a dropping nozzle. A dropping type particle manufacturing apparatus used for such a dropping method is a single tube as shown in FIG. There are 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 is maintained while maintaining the liquid droplet state. It is dripped.

As said A liquid, the liquid of the resin composition (The mixture containing the matrix resin, the polymer for hydrolysability adjustment, and the compounding agent mix | blended suitably) which forms the hydrolysable particle | grains mentioned above is used. As such a hydrolyzable particle liquid (A liquid), it is possible to directly supply a melt prepared by melt-mixing each component to the single tube nozzle 5, but the viscosity is high, so Since it is difficult to adjust the flow rate for dropping the droplets 7 adjusted to the particle size, the viscosity is adjusted to about 10 to 10,000 mPa · sec (25 ° C.) using a predetermined organic solvent, and this hydrolysis is performed. It is preferable to supply an organic solvent solution of the conductive particles as the A liquid.
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 liquid 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. The hydrolyzable particles 11 having a target particle size can be obtained by precipitation and solidification on the spot.

  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 received in the receiving tank 9 as described above. It is dripped.

  That is, in this apparatus, 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, so that the droplet 7 dropped from the nozzle 5 has the liquid A as a core. The capsule structure has the B liquid as a shell.

  In the present invention, as the liquid A that forms the core of the droplet 7, the liquid of the resin composition that forms the hydrolyzable particles described above is used as in FIG. 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 forming the hydrolyzable particles and maintains a constant particle size.

  Said A liquid (liquid of the resin composition for hydrolysable particle formation) is prepared by melt-mixing each component, and it is also possible to supply this melt directly as A liquid, but a viscosity is high. Therefore, since it becomes difficult to adjust the flow rate for dropping so that the droplet 7 adjusted to a predetermined particle size is formed, the viscosity is 10 to 1000 mPa · s using the same volatile organic solvent as described above. It is preferable to adjust this to about sec (25 ° C.) and supply this solution as liquid A.

By supplying such A liquid to the core tube 1 and supplying and dropping the above-mentioned sodium alginate aqueous solution as B liquid, droplets 7 encapsulated with A liquid as the core and B liquid as the shell are formed. However, in this case, in order to effectively perform the encapsulation, the viscosity of the sodium alginate aqueous solution used as the liquid B is preferably adjusted to be 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.
The inner diameter of the tip of the nozzle 5 as described above (the inner diameter of the core tube 1 and the outer tube 3) is set to such a range that the diameter of the finally obtained particles is within the aforementioned range, and the A liquid and The supply speed of the B liquid is also set to be in an appropriate range, but it is usually desirable that the flow ratio of the A liquid and the B liquid is appropriately set.

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. The droplets 10 thus deposited are immersed in a sodium citrate aqueous solution stretched in a receiving tank 9 ′, whereby particles 11 from which the shell of the B liquid has been removed from the droplets 10 are obtained.

The polyoxalate particles 11 obtained using the dripping nozzles of FIGS. 1 and 2 are all recovered immediately from the receiving tank 9 or 9 ′, and when they contain a solvent, they are appropriately poured into water to remove the solvent. Remove. This operation may be performed before removing the coated sodium alginate when encapsulation is performed using the apparatus of FIG.
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 target hydrolysable particles. .

  In the above description, an example in which an aqueous sodium alginate solution is used as the liquid B forming the shell is not limited to this, but the liquid A is stably coated around the liquid droplets. Any aqueous solution of a salt or the like having an appropriate viscosity capable of preventing fusion between the A liquids can be used as the B liquid. Moreover, according to the kind of B liquid, the kind of aqueous solution stretched to the receiving tank 9 can also be selected suitably.

<Application>
The hydrolyzable particles of the present invention can effectively avoid inconveniences such as dust scattering, are effectively prevented from being fused on the ground, and are easy to handle, and are formed during hydraulic crushing. It has a function of being introduced into a crack and temporarily closing the crack, and after a certain period of time, it hydrolyzes and disappears.
Therefore, it is suitably used for the preparation of drilling dispersions such as fracturing fluids used at underground resource mining sites. Especially for mining shale gas, it is used as an aqueous liquid with water as a medium together with proppants such as sand grains. It is added and used suitably as a fracturing fluid.

<Melting point measurement>
Apparatus: DSC 6220 manufactured by Seiko Instruments Inc. (differential scanning calorimetry)
Sample preparation: Sample amount 5-10mg
Measurement conditions: measured in the range of 0 ° C. to 250 ° C. at a temperature increase rate of 10 ° C./min in a nitrogen atmosphere.

<Measurement of molecular weight>
Apparatus: Gel permeation chromatograph GPC
Detector: Differential refractive index detector RI
Column: Shodex HFIP-LG (1), HFIP-806M (2) (Showa Denko)
Solvent: hexafluoroisopropanol (5 mM sodium trifluoroacetate added)
Flow rate: 0.5 mL / min
Column temperature: 40 ° C
Sample preparation:
5 mL of a solvent was added to about 1.5 mg of a sample, and the mixture was gently stirred at room temperature (sample concentration: 0.03%). After confirming that it was dissolved visually, it was filtered with a 0.45 μm filter. All samples were measured within about 1 hour from the start of preparation. The standard used was polymethyl methacrylate.

<Polymerization of PEOx>
In a 1 L separable flask equipped with a mantle heater, a liquid temperature thermometer, a stirrer, a nitrogen inlet tube, and a distillation column,
Dimethyl oxalate 472 g (4 mol)
297 g (4.8 mol) of ethylene glycol
Tetrabutyl titanate 0.40g
The liquid temperature in the flask was heated to 120 ° C. under a nitrogen stream, and normal pressure polymerization was performed.
After the start of the distillation of methanol, the liquid temperature was gradually raised to 200 ° C. to effect normal pressure polymerization, and finally 260 ml of a distillate was obtained.
Thereafter, the temperature of the liquid in the flask was reduced at a temperature of 200 ° C. and a reduced pressure of 0.1 kPa to 0.8 kPa. The obtained polymer was taken out, granulated with a crusher, and crystallized by vacuum heat treatment at 120 ° C. for 2 hours.
The obtained polymer (PEOx) had a melting point of 180 ° C. and a weight average molecular weight of 70000.

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

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

Claims (4)

Hydrolyzable particles having a dispersion structure in which fine particles of hydrolyzable polymer for adjusting the hydrolyzability of the matrix resin are distributed in the hydrolyzable matrix resin, and having an average particle size (D ₅₀ ) is in the range of 300 to 1000 μm, and the hydrolyzable particles have a roundness with a minor axis / major axis ratio of 0.8 or more.   When the hydrolyzability is shown by the weight retention when immersed in water at 70 ° C. for 168 hours, the hydrolyzable particles exhibit a weight retention of 50% or less, and the matrix contained in the hydrolyzable particles The hydrolyzable particle according to claim 1, wherein the resin has a weight retention of 90% or more.   The hydrolysable particles according to claim 1 or 2, wherein the matrix resin is polylactic acid and the hydrolyzable polymer is polyoxalate.   The hydrolyzable particle according to claim 3, wherein the polyoxalate is a copolymer having a branched copolymer unit derived from a tri- or higher functional alcohol or acid.