JP5672992B2 - Hydrophilization method of plastic surface - Google Patents

Description

  The present invention relates to a method for hydrophilizing a plastic surface, which uses a plasma treatment to hydrophilize the surface of a plastic material.

  Polymer materials such as plastic are lightweight and can be easily processed at low cost, and are therefore used as raw materials for manufacturing various products around us. Among them, most containers and packaging for storing food and drink are made of plastic. However, since plastic is originally a hydrophobic material, it cannot be bonded or printed as it is. For this reason, surface treatment using corona discharge or plasma has been attempted for the purpose of improving the adhesion and printability of the polymer material.

  For example, in Patent Document 1 below, the surface roughness of the fluororesin is increased by using methods such as plasma etching, ion beam etching, and corona discharge treatment in order to improve the low adhesion of the fluororesin surface. Then, it is proposed to form a hydrophilic thin film, and it is described that the hydrophilicity of the fluororesin surface is improved by forming the silicon hydrophilic thin film. Patent Document 2 below describes a method for improving the hydrophilicity of a plastic surface by exposing the plastic to a high electron density plasma formed using oxygen gas.

Japanese Patent No. 3274669 JP 2003-342400 A

  In the method of Patent Document 1, it is considered that the imparted hydrophilicity is dependent on the surface adhesiveness of the thin film for a sustainable period, but this point is unclear and how much hydrophilicity can be maintained. Not sure.

  In the above-mentioned Patent Document 2, it is described that the improved hydrophilicity of the polyester surface is maintained for 15 days, but it is described that polypropylene is not hydrophilized, and this method is a method limited to polyester materials. is there. Therefore, it is necessary to develop a hydrophilization method that can be applied to plastics other than polyester and can maintain the hydrophilicity of the plastic material surface for a long period of time.

  The object of the present invention is to solve the above-mentioned problems and to provide a method for hydrophilizing a plastic surface that can be applied to general-purpose plastic materials such as styrene resin and polyolefin, and the hydrophilicity imparted to the surface is sustainable for a long period of time. That is.

  In order to solve the above problems, the present inventors have conducted extensive research and found that hydrophilic deterioration over time imparted to the plastic surface can be suppressed depending on the conditions under which gas plasma is generated. The invention has been completed.

According to one aspect of the present invention, the method for hydrophilizing a plastic surface includes disposing a plastic at a position where the distance from the plasma generation position is smaller than the mean free path of the ion species, and supplying a rare gas at 1.0 × 10 ^−2. A pre-treatment for generating plasma by generating a plasma by supplying a gas pressure of less than Torr, and supplying a gas as a raw material for introducing hydrophilic groups to generate a plasma to selectively generate radicals on the plastic surface. It has a gist of having a hydrophilization treatment to act.

  According to the present invention, it is possible to efficiently modify the surface of a hydrophobic plastic, to suppress the deterioration with time of hydrophilicity imparted to the plastic surface and to maintain a long period of time, and to produce a high-quality material. Therefore, it is possible to provide useful plastic materials in medical-related fields that require biocompatibility, and in various equipment and instrument fields that require hydrophilicity of highly durable plastic materials to ensure the service life of parts, etc. .

The schematic block diagram which shows one Embodiment of the plasma generator which can implement the hydrophilization method of the plastic surface which concerns on this invention. The graph which shows the effect of the hydrophilization process in the hydrophilization method of the plastic surface which concerns on this invention. The graph which shows the effect of the pre-processing in the hydrophilization method of the plastic surface which concerns on this invention. The spectrum which shows the change of the surface by the hydrophilization method of the plastic surface which concerns on this invention. The graph which shows the influence of the gas pressure in the pre-processing of the hydrophilization method of the plastic surface which concerns on this invention. The graph which shows the influence of the to-be-processed object position in the pre-processing of the hydrophilization method of the plastic surface which concerns on this invention. The graph which shows the influence by the kind of gas in the pre-processing of the hydrophilization method of the plastic surface which concerns on this invention.

  In general, when a voltage is applied to a gas molecule, the insulation of the gas is broken at a certain voltage, and the gas molecule that has been bombarded with electrons with high kinetic energy dissociates, resulting in electrons, radicals, ions, or excited electrons. A plasma state containing chemical species is formed. Among them, ionic species rapidly disappear due to recombination with stalled electrons, but radical species have a longer life than these. Therefore, in plasma processing in a high-pressure system, the mean free path of ion species is small, and it is difficult to place an object to be processed in this, so that it is substantially a treatment with radical species. In the plasma treatment, depending on the arrangement conditions of the object to be processed, there are cases in which ion species and radical species coexist in the mean free process of ion species, and cases in which treatment is performed by radical species alone outside the mean free process of ion species. Divided into

  The inventors of the present application tried to hydrophilize the plastic surface by variously changing the plasma generation conditions when the plastic object was plasma treated. When the plastic surface was treated under specific conditions, it was applied to the plastic surface. It has been found that hydrophilicity can be sustained for a long period of time, which is related to the plasma species. Specifically, in the method for hydrophilizing a plastic surface according to the present invention, pretreatment for supplying plasma in a state where ionic species can act on a plastic object to be treated, and radical species can act on the plastic object to be treated alone. And a hydrophilic treatment for supplying plasma in a state. In the pretreatment, it is important that ion species in the plasma act on the object to be treated. In the hydrophilic treatment, radical species may selectively act on the object to be treated, and the ion species may not substantially act. It is essential.

  In the present invention, it is not certain how the pretreated ionic species function. However, the collision of the ionic species generates an active site that easily reacts with the radical species. And the ionic species are easier to supply energy to the deep part of the object to be processed than the radical species, and the radical species can be filled or densified in the deep part or in the subsequent hydrophilization treatment. It is conceivable to promote the reaction and the introduction of hydrophilic groups in the deep part of the object.

  The method for hydrophilizing a plastic surface according to the present invention will be described in detail below with reference to the drawings.

(Apparatus for carrying out the hydrophilic treatment method)
The method for hydrophilizing a plastic surface according to the present invention is carried out using an apparatus capable of generating plasma, and it is sufficient that the operating conditions of the apparatus can be set to the pretreatment and hydrophilization conditions. An example of the apparatus is an ECR plasma generator as shown in FIG. The ECR plasma generator 1 shown in FIG. 1 has a chamber 7 having a base 3 and a coil 5 for supporting a plastic workpiece S, and is removed from the exhaust port 9 using a vacuum pump (not shown). The inside of the chamber 7 is depressurized by gassing, and the internal pressure of the chamber can be controlled by adjusting the amount of gas supplied from the gas inlet 11. The direction and frequency of the microwave generated by the microwave generator 13 are adjusted by the directional coupler 15 and the tuner 17, and are introduced into the chamber 7 from the quartz window 21 at the upper part of the chamber via the waveguide 19. The plasma P is generated inside the coil 5 by electron cyclotron resonance (ECR) due to the magnetic field and microwave generated by the coil 5. The electrons in the gas molecules that have obtained energy dissociate from the atoms or collide with the gas molecules, and neutral molecules (or atoms) and ions (charged particles) are generated.

The existence range of molecules or atoms in plasma can be obtained as an average free process. As described above, since the ion free species in plasma has a smaller average free process than radical species, the generation position of the plasma and the object to be processed The ratio of the chemical species that reaches the object to be processed changes depending on the distance between the Specifically, if the distance between the plasma generation position and the object to be processed is within the mean free path of the ion species, the radical species and the ion species reach, and the arrival amount of the ion species decreases as the distance increases. Outside the mean free path of ionic species, the ionic species do not reach and the radical species reach. The mean free path can be determined according to the following formula (where R: gas constant, T: temperature, N _A : Avogadro number, σ: collision cross section, p: pressure), and if the gas pressure decreases, Since the mean free path increases, the chemical species reaching the object to be processed can also be controlled by the gas pressure for generating plasma.

Mean free process λ = RT / (2 ^1/2 × N _A × σ × p)
Therefore, a plasma generator configured such that the distance between the plasma generation position (that is, the inside of the coil) and the object to be processed can be changed by adjusting the position of the table 3 in the chamber 7, or the ion species can be adjusted by adjusting the gas pressure in the chamber. In the plasma generator configured to be able to change the mean free process, both the pretreatment and the hydrophilization treatment in the hydrophilization treatment method of the present invention can be suitably performed. In changing the distance between the plasma generation position and the object to be processed, the distance in the pretreatment is shorter than the distance in the hydrophilic treatment, and in adjusting the gas pressure, the gas pressure in the pretreatment is more than the gas pressure in the hydrophilic treatment. It is adjusted low, and the reachable distance of ion species becomes long at low gas pressure.

(Preprocessing)
In the pretreatment, the object to be processed is disposed at a position where the distance between the plasma generation position and the object to be processed is smaller than the average free process of the ion species to generate plasma, and the ion species are applied to the object to be processed. Since ion species in plasma have a shorter lifetime than radical species, they disappear rapidly due to recombination with stalled electrons, and the mean free path is small, but the object to be processed is placed within the mean free process of the ion species. In this case, the effect of pretreatment can be obtained. Therefore, regardless of the gas pressure for generating plasma, pretreatment can be performed as long as the object to be processed can be arranged in the mean free process of ion species. However, practically, when the gas pressure is reduced and the mean free path is increased, the plasma diffuses and it is easy to adjust the arrival of the ion species and the conditions are easily set. Therefore, when a low gas pressure is applied in the pretreatment, it is easy to appropriately adjust the treatment conditions and cause the ionic species to act well on the workpiece. From such a point, it is preferable to set the gas pressure to 1.0 × 10 ⁻² Torr or less, more preferably 5.0 × 10 ⁻³ Torr or less. The gas used for plasma generation in the pretreatment is preferably a gas that is inert to the object to be processed, and is preferably a rare gas such as argon, helium, neon, krypton, or xenon. You may use combining a seed | species or more. Among these, argon and helium are preferable, and argon is the most effective, and has a high effect of maintaining the hydrophilicity imparted by the subsequent hydrophilization treatment for a long period of time. The gas supplied to the pretreatment may contain a gas other than the inert gas described above, but when the ratio of the rare gas decreases, the action of the ionic species decreases, so the ratio of the rare gas (total gas flow ratio) ) Is preferably 75% or more, more preferably 90% or more.

  In the pretreatment, not only ionic species but also radical species act on the object to be treated, and the physical action of the ionic species and the chemical action of the radical species compete on the surface of the object to be treated. Due to the physical action of ionic species, the surface area of the object to be treated is increased macroscopically, and microscopically, polymer sites are broken and surface hydrogen is dissociated to increase the active sites and react with radicals. make it easier. Since argon ions are heavier than radical species or oxygen-derived chemical species, the object to be processed disposed below the plasma generation site is susceptible to the action of argon ions.

  If the gas supplied to the chamber contains a gas having a hydrophilizing action such as oxygen or nitrogen, a hydrophilic group introduction reaction can proceed simultaneously due to a chemical action by oxygen radicals or the like. However, the introduction efficiency of the hydrophilic group is actually low and the cause is not clear. However, in a state where the ionic species and the radical species compete with each other, the functional group introduced to the surface of the object by the radical species becomes an ionic species. It is thought that it is detached or activated / decomposed.

  Since the pretreatment is a treatment for activating the surface of the object to be treated, other energy supply means may be used in combination. For example, irradiation with ultraviolet rays or the like may be performed during the pretreatment.

(Hydrophilic treatment)
Hydrophilization of the plastic surface is possible without introducing hydrophilic groups, and in the treatment with rare gas plasma, the hydrophilicity is increased by roughening the surface. However, this effect alone is not sufficient, and the introduction of a hydrophilic group is necessary for hydrophilization such that the contact angle of water on the plastic surface is lowered to about 20 degrees or less. For this purpose, a gas having a hydrophilizing action is used, and a plasma having a hydrophilizing action is supplied to the chamber to generate plasma. The gas having a hydrophilizing action contains a raw material gas from which a hydrophilic group is derived, and a radical species generated from the raw material gas collides with the surface of the plastic workpiece and a hydrophilic group is introduced by a chemical reaction. Examples of the raw material gas used as a raw material for the hydrophilic group include oxygen, nitrogen, carbon dioxide, etc., but oxygen is particularly preferable in terms of the high hydrophilicity imparted by the introduced hydrophilic group, and a hydroxyl group, a carbonyl group, and the like. Is introduced. The gas supplied to the chamber does not need to be a source gas alone, and may be a mixed gas containing a rare gas such as argon, helium, neon, krypton, xenon, etc. Processing efficiency is high. Therefore, in order to suitably hydrophilize using a mixed gas of source gas / rare gas, the ratio of the source gas is preferably about 20% or more (total gas flow ratio), more preferably about 50% or more. Good. Hydrophilization treatment tends to proceed more easily when the gas pressure is higher, and this tendency becomes more prominent when a mixed gas is used. The reason for this tendency is considered to be that when the gas pressure is high, the selectivity of radicals incident on the object to be processed is high, and chemical action by radical species, that is, easy introduction of a hydrophilic group. Therefore, the gas pressure in the hydrophilization treatment is preferably adjusted to about 0.01 Torr or more, more preferably about 0.1 Torr or more in order to allow radical species to act on the object to be treated. Hydrophilization treatment by treatment is useful. Hydrophilic treatment at low pressure is possible by arranging the object to be processed outside the region where ions can reach, but higher gas pressure is better in terms of processing efficiency.

  In the pretreatment in which the ionic species are allowed to act on the object to be treated, the ionic species and the radical species compete with each other, so that the possibility of performing the pretreatment and the hydrophilization treatment at the same time is expected. However, the effect of pretreatment with ionic species cannot be sufficiently obtained when oxygen gas is used alone, and the hydrophilicity after treatment tends to deteriorate with time. For this reason, the supply gas needs to contain a rare gas such as argon. However, when ion species are caused to act by plasma using a mixed gas of oxygen and argon, the hydrophilic group introduced by the radical species is caused by the action of the ion species. Desorption occurs, making it difficult to make it hydrophilic. For this reason, it is difficult to simultaneously perform the pretreatment and the hydrophilization treatment, and it is important that the radical species selectively act after the ionic species act.

  Therefore, a hydrophilization treatment that is separate from the pretreatment is required, and even under conditions where the hydrophilization treatment proceeds simultaneously in the pretreatment (radicals derived from source gas and rare gas ions compete) It is necessary to ensure the state of treatment alone (selective action of radical species).

  The radical species is highly reactive, but the energy given when it collides with the object to be processed is relatively small, and the action on the object to be processed is considered to be limited to the vicinity of the surface. On the other hand, the ion species is heavier than the radical species and gives a large amount of energy when it collides with the object to be treated. Therefore, it is considered that the energy propagates to the deep part of the object to be treated. From this, the phenomenon that the hydrophilicity imparted to the object to be treated deteriorates with time seems to be related to the region or function in which only the ion species can act. For example, the surface of the object to be treated is roughened by collision of the ion species. As the surface area is changed, the material structure (voids, etc.) in the deep part is changed to make it difficult for the hydrophilic group introduced into the surface to gradually enter the inside, and the deep part is activated by the energy supplied to the deep part of the object by the ion species. Thus, in the subsequent hydrophilization treatment, it is easy to introduce a hydrophilic group in the deep part, and it is considered that the hydrophilic group on the surface is suppressed from entering the inside.

  The hydrophilization treatment by the selective action of radical species is considered not only to introduce hydrophilic groups, but also to have the function of returning the object to be processed by consuming the energy supplied to the object by pretreatment. It is done. The energy supplied to the object to be processed by the action of the ionic species activates the deep part of the object to be processed and the organic groups on the surface. However, it is considered that the hydrophilicity of the surface is lost, but when the residual energy is consumed by the selective action of radical species, the stability of the hydrophilic group is considered to increase.

(Embodiments and applications)
From the above, the following procedure can be cited as an embodiment of the hydrophilization method of the present invention. In this embodiment, argon gas is used as the gas supplied to the pretreatment, and oxygen gas is used as the raw material gas for introducing the hydrophilic group.

In the chamber 7, a plastic substrate is disposed as an object to be processed about 30 cm below the coil 5. While evacuating the chamber 7 with a vacuum pump, argon gas is introduced so that the chamber internal pressure becomes about 3 × 10 ⁻³ Torr, the microwave oscillator 15 is activated to generate plasma, and the object to be processed is exposed. (Pre-processing) Subsequently, oxygen or an argon / oxygen mixed gas is introduced so that the chamber internal pressure becomes about 0.1 Torr, plasma is generated, and the object to be processed is exposed (hydrophilic treatment).

  Plasma generated inside the coil is localized above the object to be processed. Since ionic species have a shorter life than radical species, they reach the object to be treated by low-pressure pretreatment. Only selectively acts on the workpiece. Oxygen radicals act selectively on the active sites generated by the pretreatment to introduce hydrophilic groups, and the active sites are stabilized. Thereby, hydrophilicity is imparted and long-term sustainability is possible. The higher the oxygen concentration in the atmosphere in the hydrophilic treatment, the higher the hydrophilicity can be imparted. In other words, the hydrophilicity imparted to the object to be processed can be adjusted by adjusting the concentration of oxygen in the argon / oxygen mixed gas.

  Since the degree of the effect of the pretreatment and the hydrophilization treatment depends on the energy supplied to the object to be treated by the treatment, the effect increases as the treatment time increases. Since the plasma generation state varies depending on the structure design of the plasma generator, etc., the arrangement of the target object and the gas supply conditions based on the hydrophilicity data actually given to the target object under certain plasma generation conditions By appropriately changing (gas pressure, concentration ratio in the case of mixed gas) and the like, the processing conditions can be optimized, and the processing time can be set according to the required hydrophilicity.

When the table 3 in the chamber 7 is movable, the pretreatment and the hydrophilic treatment can be switched by moving the table 3. In this case, for example, a mixed gas of argon and oxygen is used as the supply gas, and the object to be processed is arranged in a region where argon ions can be achieved while maintaining the chamber internal pressure at a low pressure of about 3 × 10 ⁻³ Torr. Then, pretreatment is performed by generating plasma, and thereafter, the base 3 is moved away from the coil 5 and the object to be processed is moved out of the region where ions can be achieved. Processing is performed.

  The above-described method for hydrophilizing a plastic surface according to the present invention can introduce a hydrophilic group into a stable molecular bond such as a polyolefin main chain, and thus can be applied to various plastic materials such as nylon-6, nylon-66, nylon, and the like. -11, nylon-12, nylon-610, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polyether ether ketone, poly α-methylstyrene, polycarbonate, polymethacrylonitrile, polyacrylic acid, polymethyl methacrylate, polyacrylonitrile Polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethyl methacrylate, polyvinyl acetate, poly n-butyl methacrylate, polylactic acid, polyamide, styrene-acrylonitrile copolymer, etc. It is below.

  Hereinafter, the present invention will be described in detail with reference to examples. In the following description, the percentage indicating the gas composition ratio is expressed by the total gas flow ratio in the plasma.

<Hydrophilic treatment and its effect>
A polystyrene substrate having a diameter of 25 mm was prepared as an object to be processed, and was ultrasonically cleaned with ethanol for 2 minutes and air-dried. This was placed in a chamber 7 of an ECR plasma generator (microwave oscillation frequency: 2.45 GHz) as shown in FIG. 1 and placed on a table 3 about 30 cm below the coil 5. While evacuating the chamber 7 with a vacuum pump, argon gas is supplied to the chamber at a flow rate of 15 sccm to maintain the chamber internal pressure at 3 × 10 ⁻³ Torr, plasma is generated under the condition of a coil current of 30 A, and the substrate is left for 1 minute. Plasma treatment was performed.

  Further, a polystyrene substrate subjected to plasma treatment with different gas pressures was obtained in the same manner except that the chamber internal pressure was changed by changing the flow rate of argon gas in the above operation.

  Further, the polystyrene substrate subjected to plasma treatment with different gas composition by changing the gas supplied to the chamber in the above operation from argon gas to argon / oxygen mixed gas, and the polystyrene substrate subjected to plasma treatment with different gas pressure Got.

  In order to evaluate the hydrophilicity of the surface of each of the polystyrene substrates obtained as described above, 2 ml of pure water was dropped onto an arbitrary portion of the substrate with a syringe, and the contact angle was measured using a contact angle meter. The measurement was performed by dropping water droplets at two locations, and at each of the two water droplets at two locations, and calculating an average value of the four values. For reference, the contact angle was also measured for an untreated polystyrene substrate. The results are shown in the graph of FIG. In general, it is considered that the hydrophilicity increases as the contact angle decreases.

  Originally, the contact angle of the hydrophobic polystyrene substrate surface is high, but according to FIG. 2, it can be seen that the plasma treatment reduces the contact angle of the substrate surface with water and imparts hydrophilicity. Furthermore, when the oxygen ratio in the supply gas (argon / oxygen) and the gas pressure in the chamber are changed, the contact angle of the substrate surface immediately after the plasma treatment changes, and the oxygen ratio in the gas and the chamber internal pressure increase, respectively. It can be seen that the more hydrophilic the effect is. This suggests that oxygen-derived ion species or active species (radicals) generated in the plasma greatly contribute to imparting hydrophilicity.

  In general, in plasma treatment, physical action by ion species (collision on the surface) and chemical action by radical species (chemical reaction with the surface) compete with the substrate. As it rises, plasma is localized between the coils above the substrate. Therefore, increasing the gas pressure during processing increases the distance between the plasma and the substrate, and ion species having a short lifetime tend to disappear before reaching the substrate, whereas radical species reach the substrate and reach the substrate. It will contribute to the action and modification with the surface. Therefore, it is considered that the hydrophilicity imparting effect on the high pressure side seen in FIG. 2 is brought about by the selective reaction of radical species with the surface, and the contact angle at a gas pressure of 0.1 Torr is the oxygen ratio of the supply gas. That the hydrophilization is an action by oxygen-derived radicals. Further, the contact angle when the gas pressure is low clearly varies depending on the presence or absence of argon (that is, a gas other than oxygen). That is, it is understood that the hydrophilic group introduced by oxygen is removed by argon ions. From this, it is considered that the ionic species have the action of activating the substrate surface to dissociate or desorb the organic groups, and desorb the hydrophilic groups introduced by the radical species. When it exists, it is thought that the detachment | desorption of the hydrophilic group introduce | transduced into the board | substrate becomes remarkable.

  Therefore, it can be seen that, in order to suitably obtain the hydrophilicity imparting effect by the hydrophilization treatment, it is preferable to carry out in a state where the raw material gas concentration of the hydrophilic group is high at a high gas pressure at which radical species easily act on the object to be treated.

  When a polystyrene substrate is treated by atmospheric pressure plasma (containing a small amount of oxygen derived from the atmosphere) using argon gas, the contact angle of the surface is reduced to about 12 ° C. by a short treatment of 2 seconds, and high hydrophilicity is obtained. It is confirmed that it can be obtained. Since this treated substrate has not been pretreated, the contact angle increased to 50 degrees after 6 days, but it is possible to maintain high hydrophilicity for a long period of time by combining with the pretreatment. It is clear from the experimental results.

<Pretreatment and its effects>
(Sample preparation)
A 25 mm × 25 mm polystyrene substrate was prepared, ultrasonically washed with ethanol for 2 minutes, and air-dried. This was put in a chamber of an ECR plasma generator (microwave oscillation frequency: 2.45 GHz) and placed on a table 3 about 30 cm below the coil 5. While evacuating the inside of the chamber 7 with a vacuum pump, argon gas is supplied to the chamber at a flow rate of 15 sccm, and the chamber internal pressure is maintained at 3 × 10 ⁻³ Torr to generate plasma under the condition of the coil current 28A. Plasma treatment was performed for a minute (pretreatment). Thereafter, as a hydrophilization treatment, the flow rate of the supply gas is changed to argon 100 sccm and oxygen 300 sccm to obtain an argon / oxygen mixed gas (oxygen content ratio 75%), the chamber internal pressure is maintained at 0.1 Torr, the coil current Plasma was generated under the condition of 30 A, and the substrate was plasma treated for 3 minutes (main treatment) to obtain a polystyrene substrate of Sample 1.

  Moreover, the polystyrene substrate of the sample 2 was obtained by performing the same operation as the above-mentioned sample 1 except not performing pre-processing and changing the time of this process to 4 minutes.

(Measurement of contact angle)
For each of Samples 1 and 2 and the untreated polystyrene substrate, the surface contact angle with water was measured in the same manner as described above. Furthermore, these substrates were stored, and changes with time in the contact angle of the surface were examined. The results are shown in the graph of Table 3.

  In order to confirm whether or not the low-molecular compound has an effect on the contact angle, a three-piece polystyrene substrate treated according to the procedure of Sample 2 is prepared and washed with pure water before the contact angle is measured. A comparison was made between what was immersed in water and washed for 1 minute and then air-dried) or ethanol washed (soaked in ethanol and ultrasonically washed and air-dried for 1 minute) and one that was not washed. As a result, the contact angle (average) of the substrate was 20 degrees when not cleaned, 20.7 degrees after cleaning with pure water, and 19.05 degrees after cleaning with ethanol, and there was virtually no change due to cleaning. . Therefore, it is clear that the change in hydrophilicity of the substrate over time is not due to the loss of low molecular weight compounds due to decomposition.

(Sample evaluation)
According to FIG. 3, the untreated substrate does not show a large change in contact angle with time, and its surface properties are almost constant. On the other hand, in the substrates of Samples 1 and 2 that have been subjected to the plasma treatment, the contact angle increases with the passage of time after the plasma treatment. However, the sample 1 and the sample 2 have the same plasma irradiation time, but the degree of increase in the contact angle is greatly different. In the sample 1 subjected to the pretreatment, the increase in the contact angle is suppressed. In particular, since a contact angle as low as about 27 degrees is maintained even after 82 days from the plasma treatment, it is clear that the pretreated substrate suppresses deterioration of the imparted hydrophilicity with time.

Since argon plasma is generated at a low pressure of 10 ⁻³ Torr in the pretreatment, the plasma diffuses into the chamber more widely than in the hydrophilic treatment, and the physical action of argon ion species reaches the substrate surface. As a result, the surface area of the substrate increases macroscopically, and the reaction sites increase by microscopically cleaving polystyrene molecular chains, which may improve the reaction efficiency of oxygen-derived radicals in the subsequent hydrophilization treatment. . In addition, it is considered that the structural change due to the action of the ionic species works favorably for immobilizing the hydrophilic element.

<Change in hydrophilization>
In order to investigate the change in the surface state of the substrate due to the plasma treatment, the substrate of the sample 1 and the untreated substrate were analyzed by X-ray photoelectron spectroscopy (XPS). In the analysis, the detection angle of the detector was set to 45 degrees with respect to the substrate surface. The obtained spectrum is shown in FIG.

According to FIG. 4, polystyrene is a molecule composed of only carbon and hydrogen, and its spectrum is derived from the C—C bond or the C—H bond appearing at 285.0 eV, the C═C bond appearing at 291.5 eV. It consists only of the peak attributed to π-π ^* . On the other hand, in the spectrum after the plasma treatment, the peak of 285.0 eV becomes broad and the skirt spreads to the high energy side. In this region, it is generally known that a peak derived from carbon to which a functional group derived from oxygen is bonded occurs. When the spectrum was fitted with a Gaussian function in order to grasp the bonded functional group, C = C (284.4 eV), C—C / C—H (285.0 eV), C—O (286.6 eV), C ═O (288.0 eV), O—C═O (289.1 eV), and π-π ^* (291.5 eV) matched. This indicates that the functional group containing oxygen was bonded to polystyrene by plasma treatment, and these are considered to determine the hydrophilicity of the substrate surface. Therefore, it is presumed that changes in the surface functional groups with time are included in the factors of hydrophilic deterioration with time observed when measuring the contact angle. In order to verify this, the spectrum for several days after the plasma treatment was measured, and the time-dependent change in the area ratio with respect to the peak total area of the portion attributed to each functional group was examined. Only C = O was found to decrease with time. From this, it is considered that O—C═O is mainly involved in the hydrophilicity of the polystyrene surface, and the disappearance from the surface is one of the hydrophilic deterioration factors. Moreover, it is considered that the change in the surface structure in the physical action of the argon ion species in the pretreatment is related to the delay of the disappearance rate of O—C═O, and suppresses the deterioration of hydrophilicity.

  Polystyrene substrates of Samples 3 to 7 were prepared according to the following procedure, and used for the following evaluation together with Sample 1 of Example 1.

(Sample 3)
A polystyrene substrate of Sample 3 was obtained by performing the same operation as Sample 1 of Example 1 except that the flow rate of argon gas in the pretreatment was increased and the chamber internal pressure was maintained at 1.5 × 10 ⁻² Torr. .

(Sample 4)
A polystyrene substrate of Sample 4 was obtained by performing the same operation as Sample 1 of Example 1 except that the flow rate of argon gas in the pretreatment was increased and the chamber internal pressure was maintained at 1.5 × 10 ⁻¹ Torr. .

(Sample 5)
A polystyrene substrate of Sample 4 was obtained by performing the same operation as Sample 1 of Example 1 except that the position of the table 3 in the chamber was lowered 100 mm downward.

(Sample 6)
Similar to Sample 1 of Example 1 except that the position of the base 3 in the chamber was lowered 100 mm downward, the flow rate of argon gas in the pretreatment was increased, and the internal pressure of the chamber was maintained at 1.5 × 10 ⁻² Torr. The operation was performed to obtain a polystyrene substrate of Sample 6.

(Sample 7)
The same as Sample 1 of Example 1 except that the position of the table 3 in the chamber was lowered 100 mm downward, the flow rate of argon gas in the pretreatment was increased, and the chamber internal pressure was maintained at 1.5 × 10 ⁻¹ Torr. The operation was performed to obtain a polystyrene substrate of Sample 7.

(Sample evaluation)
For each of the polystyrene substrates of Samples 3 to 7, the contact angle of the surface with water was measured in the same manner as described in Example 1. Furthermore, these substrates were stored, and changes with time in the contact angle of the surface were examined. The results of samples 3 and 4 are shown in the graph of FIG. 5 together with the results of sample 1, and the results of samples 5 to 7 are shown in the graph of FIG.

  According to FIG. 5, it is clear that the hydrophilic durability of the substrate surface varies depending on the chamber internal pressure in the pretreatment, and the hydrophilic sustainability imparted to the substrate is high when the pretreatment is performed at a low chamber internal pressure. . Since the ion species in the plasma easily act on the substrate when the chamber internal pressure is low, it can be considered from the results of FIG. 5 that the ion species in the plasma acts on the substrate in the pretreatment. This point is supported by the results of FIG. 6 with samples 5-7 lowered the substrate position away from the plasma for the following reasons.

The difference between the result of FIG. 5 and the result of FIG. 6 is due to the change of the substrate position. When these are compared, the deterioration of the hydrophilicity of the substrate surface over time becomes more noticeable by moving the substrate away from the plasma. It is clear that the same result is obtained regardless of the chamber internal pressure. Since the average free path of argon ions at 1.0 × 10 ⁻³ Torr and 20 ° C. is calculated to be about 60 mm, the 100 mm substrate position drop in samples 5 to 7 is caused by the arrival of argon ions in the plasma. This means that the substrate is surely excluded from the range to be obtained. Therefore, the results of FIG. 6 are those in which argon ions do not act on the substrate, and the difference between the results in FIG. 5 and FIG. 6 is attributed to the effects of argon ions in the pretreatment. That is, the difference between sample 1 and sample 5 is due to the presence or absence of the action of argon ions. The difference between Sample 1 and Sample 5 having a low internal pressure in the pretreatment is because the mean free path of ionic species at low pressure is long.

  A polystyrene substrate subjected to plasma treatment was prepared by performing the same operation as Sample 1 of Example 1 except that the gas supplied in the pretreatment was changed from argon to helium, hydrogen, nitrogen, or oxygen.

  About each of the obtained polystyrene board | substrate, the contact angle with respect to the surface water was measured like the above-mentioned. Furthermore, these substrates were stored, and changes with time in the contact angle of the surface were examined. These results are shown in the graph of FIG.

  According to FIG. 7, the persistence of the hydrophilicity of the substrate surface is the highest when argon gas is used in the pretreatment, followed by helium gas and hydrogen gas. This is probably because the energy supplied at the time of collision differs depending on the weight of the ions. When oxygen gas is used, the hydrophilicity immediately after is high, but the deterioration with time of hydrophilicity is not suppressed so much, and even when nitrogen gas is used, the deterioration with time of hydrophilicity is not so suppressed. From this, it is considered that the gas having low reactivity with the object to be processed is more suitable for pretreatment with ionic species.

  When nitrogen gas is used, the hydrophilization effect is small compared to other gases because the nitrogen-containing groups are introduced by the nitrogen-derived radicals competing in the pre-treatment, so that the oxygen-containing groups in the subsequent hydrophilization treatment are reduced. It is thought that the introduction is reduced and the hydrophilicity of the nitrogen-containing group is lower than that of the oxygen-containing group.

  The surface modification of hydrophobic plastics is performed efficiently to provide plastics with improved hydrophilic sustainability on the surface. Therefore, medical-related fields that require biocompatibility and highly durable plastic materials. It is possible to provide a plastic material useful in various fields of equipment / instruments that require hydrophilization, and it is useful for improving the service life and functionality of parts and the like.

The

1: ECR plasma generator, 3: stand, 5: coil, 7: chamber,
9: Exhaust port, 11: Gas inlet port, 13: Microwave generator,
15: Directional coupler 15, 17: Tuner, 19: Waveguide 19,
21: Quartz window.

Claims (5)

A plastic is placed at a position where the distance from the plasma generation position is smaller than the mean free path of the ion species, and a rare gas is supplied at a gas pressure of 1.0 × 10 ⁻² Torr or less to generate plasma, thereby generating ions. Pretreatment to act on the surface;
A method for hydrophilizing a plastic surface, comprising: supplying a gas as a raw material for introducing a hydrophilic group to generate plasma to selectively cause radicals to act on the plastic surface. In the pretreatment, the plastic surface is activated by the action of ions, and in the hydrophilization treatment, ions do not substantially act on the plastic surface, so that the stability of hydrophilic groups introduced into the plastic surface by radicals is increased. Item 2. A method for hydrophilizing a plastic surface according to Item 1. The rare gas includes at least one selected from argon, helium, neon, krypton, and xenon, and the gas supplied in the hydrophilization treatment includes at least one selected from oxygen, nitrogen, and carbon dioxide. The method for hydrophilizing a plastic surface according to claim 1 or 2. The method for hydrophilizing a plastic surface according to any one of claims 1 to 3, wherein a gas pressure in the hydrophilization treatment is 0.01 Torr or more. The method for hydrophilizing a plastic surface according to any one of claims 1 to 4, wherein the distance between the plastic and the plasma in the hydrophilization treatment is set farther from the mean free path of ionic species.

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