Polyacrylic acid (SALT), polyacrylic acid (SALT)-based water-absorbing resin, and process for producing same

Abstract

A polyacrylic acid (salt), or a polyacrylic acid (salt)-based water-absorbing resin, contains a tracer for detecting various troubles in the water-absorbing resin during the period from the production of the water-absorbing resin to the use and discard thereof by a consumer. The polyacrylic acid (salt)-based water-absorbing resin has a stable carbon isotope ratio, as determined by accelerator mass spectrometry, of less than −20% and a radioactive carbon content of 1.0×10−14 or mole. The polyacrylic acid (salt)-based water-absorbing resin has: a CRC of 10 [g / g] or mole; an AAP of 20 [g / g] or mole; an Ext of 35 wt. % or less; a content of residual monomers of 1,000 ppm or less; a PSD in which the proportion of particles having a particle diameter of 150 μm or larger but less than 850 μm is 90 wt. % or more; and an FSR of 0.15 [g / g / s] or more.

Description

TECHNICAL FIELD[0001]The present invention relates to polyacrylic acid (salt), polyacrylic acid (salt)-type water-absorbing resin and process for producing same. More specifically, it relates to a water-absorbing resin which is easy to identify and trace.BACKGROUND ART[0002]A water-absorbing resin (SAP / Super Absorbent Polymer) is a water-swelling and water-insoluble polymer gelling agent and has been used for mainly disposable uses including absorbing articles such as paper diapers and sanitary napkins and the like, further, water retention agents for agriculture and horticulture, and water-stopping materials for industrial use and the like (Non-patent Literature Document 1). For these water-absorbing resins, a number of monomers and hydrophilic polymers have been suggested as raw materials. However, a polyacrylic acid salt type water-absorbing resin made mainly from an acrylic acid is mainstream thereof and most of the water-absorbing resins manufactured all over the world are cros...

AI Technical Summary

Benefits of technology

The present invention allows for the identification and tracking of a water-absorbing resin that is distributed on the market. This is done by analyzing the physical properties of Carbon 13C and Carbon 14C / C. Additionally, the invention provides a CO2-reducing and carbon-neutral water-absorbing resin as a result of using a C3 plant as a carbon source for acrylic acid to control the amount of Carbon 13C.

Problems solved by technology

And now, most of commercialized water-absorbing resins have a polymer structure of polyacrylic acid sodium salt and are insoluble in a solvent, so that it is impossible to measure their molecular weights as polymers.

Accordingly, in the case where produced water-absorbing resins are actually used for disposable diapers, sanitary napkins, greening humectants, humectants for agriculture and horticulture, digestion gel, and the like after distributed through various distribution channels and subsequently discarded, it is difficult to determine in which factories, which plants, and which production lines such water-absorbing resins and their used hydrogels are produced and even if a certain water-absorbing resin causes a trouble at the time of its use or after its use or even if it is tried to assess the effect on environments, degradability in the ground after landfill or the like, it is difficult to distinguish which water-absorbing resin manufacturer, which factory, which plant, or which production line produced the water-absorbing resin.

Many methods for producing various kinds of water-absorbing resins as disclosed in the following Patent Documents 1 to 21 have been proposed so far, but they do not disclose a method for solving all the troubles which possibly occur in the process for producing a water-absorbing resin.

Consequently, when a trouble occurs, the production method is revised and in general, the process for producing a water-absorbing resin involves many steps such as a monomer preparation step, a polymerization step, a drying step, a pulverizing step, and a surface-crosslinking step and in some production methods, many different raw materials are used and the production proceeds following a complicated course through many steps, and therefore it is difficult to pursue a cause of a trouble.

Also, there are troubles which are discovered after time passes, such as coloration with the lapse of time of a water-absorbing resin as a representative, so that it is difficult to investigate the cause from the production method.

In recent years, the physical properties required by users represented by disposable diaper manufacturers are more or less similar, and therefore, even if water-absorbing resins are taken out of disposable diapers etc., their physical properties are often similar and consequently, it is difficult to improve the precision of the identification of a manufacturer and a distributor based on the water-absorbing resins.

It is conceivable to add a tracer substance to a water-absorbing resin; however, addition of a tracer not only causes an adverse effect on the cost and safety but also sometimes deteriorates the performance and whiteness of the water-absorbing resin.

Also, such a problem is found occurring not only in the case of a water-insoluble and water-swelling polyacrylic acid (salt) (also referred to as a polyacrylic acid (salt)-type water-absorbing resin) but also in the case of a water-soluble polyacrylic acid (salt) (also referred to as a water-soluble polymer).

Also, a water-absorbing resin has another problem that the ratio of acrylic acid is high, in other words, the cost of a water-absorbing resin significantly depends on the price of propylene (petroleum).

Also, in addition to the above-mentioned problem, since the water-absorbing resin containing acrylic acid as a main component is mainly used for disposal use such as disposable diapers and the like, the water-absorbing resin has another issue of stable supply of a raw material in terms of the cost.

To deal with that, there is a technique known for obtaining a water-absorbing resin, for example, a carboxymethyl cellulose crosslinked body and the like by crosslinking starch or cellulose, but the physical properties are inferior as compared with those of a polyacrylic acid (salt).