JPH04309536A - Radiation grafting process and grafted product - Google Patents

Abstract

PURPOSE:To provide the title process useful for obtaining a grafted product excellent in metal adsorptivity, strengths, etc., by subjecting a polymer base to specified irradiation before grafting a specified monomer onto the base. CONSTITUTION:A polymer base (e.g. PE film) is irradiated with a radiation (e.g. accelerated electron beams) at a dose sufficient to crosslink the base, before vinyl monomer (e.g. acrylic acid) is grafted onto the base.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-grafted polymer base material that can be used, for example, as a metal ion adsorbent, and a method for producing the same.

0002

[Prior Art] Generally, in order to obtain rapid metal adsorption properties, the large surface area of polymer particles or fibrous base materials is utilized, and some metal adsorbent such as acrylic acid, methacrylic acid or styrene sulfone is applied to the surface of these resins. A method of providing an active layer of acid, 2-acrylamido-2-methylpropanesulfonic acid, amidoxime group, etc. has been used. The conditions for using such metal adsorbents are various, and when used for wastewater treatment or metal recovery from seawater, the adhesion between the polymer base material and the active layer is an important issue. When the active layer is fixed by heat curing or the like, the durability of the base material is sufficient, but the adhesiveness with the active layer is insufficient, making it unsuitable for long-term use. As a method to overcome these drawbacks, studies have been conducted on a grafting reaction in which the polyolefin resin of the base material and the substance constituting the active layer are bonded directly through chemical bonds. The grafting reaction itself involves electron beam irradiation, γ-ray irradiation, light irradiation,
Although it can be initiated by many means such as plasma treatment, corona treatment, flame treatment, etc., radiation irradiation such as electron beams and gamma rays is preferred from a practical standpoint.

[0003] These grafting reactions by irradiation with radiation are not only easy to perform, but also have the advantage that the reaction is fast due to the high dose rate, the irradiation can be carried out at low temperatures, and the amount of grafting is large. In the grafting reaction by radiation irradiation, it is efficient to make the polymer base material and the monomer to be grafted coexist and irradiate them at the same time (simultaneous irradiation method). (For example, the monomer requires a relatively low G value, and the polymer base material requires a high G value). Furthermore, not only is the polymerization of the monomer alone unavoidable, but this monomer polymer must be washed with water or extracted after the grafting reaction. Therefore, it is difficult to separate, which poses a practical problem.

[0004] As a grafting method by radiation irradiation, a method in which only the polymer base material is irradiated with radiation in advance and then reacted with the monomer (pre-irradiation method) can suppress the homopolymerization of the monomers mentioned above; However, in this radiation irradiation reaction, the penetrating power of the active energy rays is too large, which activates even the inside of the particles, fibers, and films of the polymer base material. It has the disadvantage that it can be diffused inside. In particular, this drawback poses the dilemma that if the reaction is carried out at a high temperature to increase the grafting reaction rate or if a solvent is used to make the reaction uniform, diffusion into the interior of the polymer base material will be further promoted. Ta. Diffusion of such monomers into the polymer base material is
This not only reduces metal adsorption efficiency, but also reduces the mechanical strength of the polymer base material due to swelling during use, and the graft compound inside the film slows metal adsorption and desorption, resulting in slow processing speed. This was a serious problem in practical terms.

[0005] In general, it can be considered that the radical species generated inside a polymer base material by radiation irradiation is proportional to the radiation dose. At a low radiation dose where crosslinking of the polymer base material is negligible, the grafting rate at a given reaction time is almost proportional to the radiation dose. As the reaction time increases, the grafting rate also increases, and the graft layer progresses from the surface of the polymeric substrate toward the inside. It can be seen that the increase in the grafting rate and the decrease in the thickness of the unreacted polymer base material are almost proportional, but if the graft layer spreads over the entire thickness of the polymer base material, that is, the unreacted polymer base layer disappears. At this point, this grafted polymeric substrate begins to rapidly swell and expand.
Moreover, the mechanical strength originally possessed by the polymer base material is extremely reduced. In order to obtain a grafted product while maintaining the mechanical strength of the polymer base material, use a solvent that does not dissolve or swell the base material, and shorten the reaction time to prevent the graft layer from advancing inside the polymer base material. There is no choice but to stop it, but in this case there is a dilemma in that the amount of monomer grafted onto the surface of the polymer base material is small, the grafting ratio becomes small, and the metal adsorption ability decreases. This dilemma can be solved not only by metal adsorption, but also by applying graft reaction technology to polymer substrates for ion exchange, immobilization of enzymes and bacteria, improved adhesion, antistatic properties, antifogging properties, and lithography. Naturally, this also poses a problem.

[0006]

[Problems to be Solved by the Invention] Therefore, the present invention aims to create a highly adhesive and durable active layer only on the surface of a polymeric base material by a grafting reaction at a high concentration, thereby achieving a grafting structure with practical strength. A treated polymer base material is created.

[0007]

[Means for Solving the Problems] As a result of intensive research into means for solving the above-mentioned problems, the inventors have discovered the following method. That is, by first irradiating the polymer base material with radiation to crosslink the polymer base material, and then performing a graft reaction with a monomer having a vinyl group, the graft layer is formed only on the surface of the polymer base material. This is the invention of a radiation irradiation grafting method that can be created by limiting the method, and a grafted product having a graft layer only on the surface of a polymer base material crosslinked by radiation irradiation. In the present invention, "irradiation sufficient to crosslink the polymeric base material" refers to radiation irradiation sufficient to crosslink the polymeric base material such that the gel fraction becomes 40% or more. The amount of radiation required to achieve a gel fraction of 40% or more differs depending on the type of polymer, but typically electron beam irradiation of 8 Mrad or more is sufficient for low-density polyethylene and 12 Mrad or more for high-density polyethylene. . Incidentally, irradiation with radiation exceeding 128 Mrad is not preferable since it is economically inefficient and may also reduce the mechanical strength of the polymer base material.

[0008] It is clear that when the polymer base material is irradiated with radiation to crosslink it in advance and then the graft reaction with the monomer is carried out as in the present invention, it is completely different from the previously known pre-irradiation graft reaction. It became. That is, firstly, the grafting rate over a certain period of time decreases as the pre-irradiation dose increases. This is thought to be because the diffusion rate of the monomer into the polymer base material is suppressed by the effect of crosslinking of the polymer base material. Therefore, the position of the graft layer is relatively limited to the surface. Second, although the grafting rate increases with reaction time, the graft layer remains relatively on the surface of the polymeric substrate, and the thickness of the unreacted polymeric substrate decreases only slightly. This is because a sufficient amount of radicals exist on the surface of the polymer base material and within the graft layer, so the monomer diffuses inside the graft layer and captures the radicals within the graft layer before reaching the unreacted polymer base material. This is thought to be due to a reaction. Therefore, a large amount of unreacted polymer base material remains, and the grafting ratio reaches a high value while maintaining high mechanical strength. The present invention will be explained in detail below.

[0009] The polymer base material referred to here is polyethylene,
Polypropylene, polystyrene, polymethylpentene
1. Radiation crosslinked resins or copolymer resins such as polysulfone, polyacrylate, polyacrylamide, polyvinyl chloride, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinylpyrrolidone, and similar vinyl monomers such as polyisobutylene and polyvinylidene chloride. It cannot be applied to radiation-degradable polymers such as. These distinctions are influenced by the conditions during radiation irradiation (temperature, atmosphere), so depending on the conditions, not only polyolefin resins but also nylon, polydimethylsiloxane, Teflon, etc. can be used as long as the resins crosslink by radiation irradiation. The morphology of these polymeric substrates is
Basically, it can be of any shape such as plate, rod, sheet, film, fiber, bead, powder, hollow fiber, etc.

[0010] The radiation referred to here particularly refers to accelerated electron beams and γ
A beam is preferable, and in particular, as an electron beam characteristic, the accelerating voltage is at least 10 Kv or more in terms of penetrating power and activation efficiency. Examples of electron beam accelerators include electrocurtain system, scanning type, double scanning type, Van de Graaff, Any cold cathode or the like may be used. The crosslinking of the polymer base material referred to here can be simply measured by the gel fraction using a solvent that can dissolve the polymer base material, and the effect of the present invention is significant when the gel fraction is 40% or more. appears in Note that when irradiating radiation, high oxygen concentrations may lead to deactivation of grafted active species (mainly free radicals) or collapse of polymers due to oxidation reactions, so replacement with an inert gas such as nitrogen or helium is necessary. It is preferable to reduce the oxygen concentration. However, this is not the case when peroxide is used as the grafting active species.

The monomers used in the present invention to form the metal-adsorbing active layer by grafting include vinyl groups necessary for radical polymerization, and carboxyl groups, sulfonic groups, and phenolic groups necessary for metal adsorption (ionic bonding, chelate formation). A vinyl monomer that directly has a hydroxyl group, a thiol, an amino group, a phosphoric acid group, a cyano group, an amino group, an amidoxime group, etc., or into which these metal-adsorbing functional groups can be introduced after grafting can be used. For example, acrylic acid, methacrylic acid, acrylamide, acrylonitrile, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinyl acetic acid, styrene phosphoric acid, divinylbenzene, styrene, vinylaniline, vinylpyrrolidone, glycidyl methacrylate, glycidyl acrylate. Examples include. The grafting reaction can be achieved by reacting with the monomer directly, using a solvent, or reacting with a vaporized monomer after irradiation. Generally, the reaction rate is often slow when a monomer is used alone, so it is advantageous to react in a solution system using a solvent. In order to prevent homopolymerization of the monomer alone, a radical polymerization inhibitor such as Mohr's salt, a redox additive such as metallic copper or cuprous chloride, or a polymerization inhibitor such as hydroquinone monomethyl ether may be used in combination. .

0012

[Function] In the radiation irradiation grafting reaction, the crosslinking structure of the polymer base material due to radiation irradiation restricts the diffusion of monomers having vinyl groups into the interior of the polymer base material during the grafting reaction, resulting in grafting. By limiting the position to only the surface of the polymer base material, it is possible to obtain a grafted base material with high efficiency and high strength.

[0013]

[Examples] The present invention will be explained in detail below with reference to Examples, but the content of the present invention is not limited to the Examples. Example High-density polyethylene film with a thickness of 95 μm (density 0.
963g/cm3) with nitrogen gas (manufactured by ESI, 175/15/20, oxygen concentration 50pp)
m or less, acceleration voltage 175 kv) 12 Mrad, 1
6Mrad, 32Mrad, 64Mrad, and 12
Electron beam irradiation was performed to give each absorbed dose of 8 Mrad. The irradiated polyethylene film was degassed in advance by nitrogen gas replacement and placed in a 50% acrylic acid aqueous solution for 7 days.
The reaction was carried out at 0°C. In order to maintain a constant grafting rate, the reaction time varies depending on each irradiation dose. The grafted polyethylene film was quickly poured into a large excess of methanol to stop the reaction, and then the grafted layer was washed by refluxing in methanol for one day. After vacuum drying, the graft ratio was calculated by weight measurement, the graft layer was neutralized with 5% potassium hydroxide solution, washed with water, vacuum dried, and the diffusion state of acrylic acid inside the polyethylene film was measured using a scanning electron microscope. was measured. A polyethylene sample that had been irradiated with an electron beam under the same conditions apart from the graft reaction was placed in a glass filter and weighed, then refluxed in toluene for 48 hours, recovered, and weighed again to determine the gel fraction.

Comparative Example The absorbed dose due to electron beam irradiation was 1 Mrad, 2 Mrad,
A grafting reaction of acrylic acid was carried out on a polyethylene film in the same manner as in the example except that the amounts were changed to 4 Mrad and 8 Mrad. Results The results of Examples and Comparative Examples are summarized in Table 1. The gel fraction, graft ratio, and monomer diffusivity were calculated using the formulas shown below, and the strength and metal adsorption properties were calculated using the methods shown below. Gel fraction = 100 x (weight after solvent extraction) / (weight before solvent extraction) Grafting rate = 100 x (weight after grafting - weight before grafting) / (weight before grafting) Monomer diffusivity = 100 - 100 × (Thickness of the film other than the graft layer after grafting) / (Thickness of the film before grafting) Strength: The maximum tensile strength of the grafted polymer base material compared to the ungrafted polymer base material that has been irradiated with the same amount of electron beams. Relative value. As the electron beam irradiation dose increases from 1 Mrad to 64 Mrad, the tensile strength of the ungrafted polymeric substrate increases by approximately 10%. The grafted polymeric substrate was measured in a wet state. Metal adsorption: When immersed in a copper ion solution with a concentration of 0.1M for 15 minutes, the amount of copper ions adsorbed per unit weight of polyacrylic acid by the 1Mrad irradiated sample of the comparative example was 100%.
Values converted as % under the same conditions.

[0015]

[Table 1]

[0016]

[Effects of the Invention] As is clear from the monomer diffusion results in Table 1, by irradiating the raw material film with sufficient electron beam to crosslink it before the grafting reaction, the grafting reaction position can be limited to the film surface. Ta. The method of the present invention not only enables high-density surface treatment, but also makes it possible to obtain a high-strength surface-treated film that reflects the mechanical strength of the original film. The metal adsorption of such a grafted polymer base material in which the grafting positions were limited to the surface was higher than that in a grafted polymer base material in which the grafting positions were spread over the entire polymer base material.

Claims (2)

[Claims] Claim 1: Radiation irradiation grafting in which a polymer base material is irradiated with radiation to crosslink the polymer base material in advance, and then a graft reaction is performed between the polymer base material and a monomer having a vinyl group. Method. 2. A grafted product having a graft layer only on the surface of a polymer base material crosslinked by radiation irradiation.