JPS6028860A - Method for coating inside surface of vessel or pipe body - Google Patents

Abstract

PURPOSE:To effect a quick curing reaction of a coating surface by coating a base resin prepolymer of a low viscosity contg. no hardener on the inside surface of a vessel then spraying the hardener so as to fill the same in the vessel. CONSTITUTION:A resin material consisting of a polyisocyanate prepolymer contg. a free isocyanate group is coated on the inside surface of a vessel or pipe body. A hardener consisting of ammonia or amine is thereafter sprayed in the vessel or the pipe body so as to be filled therein. Then the surface of the coating is quickly cured and therefore the uniform and continuous coating having no pinholes is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coating the inner surface of a container or a small diameter tube with a base resin and a hardening material.

Metal or plastic containers (cylinders, tanks, etc.) are sometimes coated on their inner surfaces for various purposes. For example, for iron cylinders, the inner surface is rust-proofed,
Further, in the case of cylinders made of other non-rust metal materials (stainless steel, aluminum, etc.), the inner surface is coated primarily to prevent reaction between the sealed contents and the cylinder material. On the other hand, in plastic tanks, the inner walls of the tank are sometimes coated to protect them from the contents. In view of its purpose, the inner surface of such a container must be coated uniformly and reliably, that is, to form a continuous coating without uneven coating, uncoated areas, pinholes, etc.

Conventionally, the inner surface of such a container has generally been painted by inserting a spray gun through the opening. However, with this method, for example, the opening of a cylinder is small and long, making it difficult to paint.
Uniform coverage is difficult. In particular, the shoulder area around the neck of the opening is extremely difficult to paint because it is shaded by the spray pattern, often resulting in uneven coating and uncoated areas. Furthermore, in the case of plastic tanks, the shoulder below the neck of the opening is generally sharply curved from a negative angle to approximately a right angle, so problems such as uneven coating and uncoated coating due to the above-mentioned causes are still noticeable.

In order to solve these problems, it is natural to think of a method of injecting a coating material from the opening of the container to be coated and coating the inner surface while moving the container, but this method has not been used conventionally for coating the inner surface of containers. Since the coating material is already completed as a face (it can form a cured film as it is) and has a high viscosity, it is difficult to flow, so it must be coated uniformly over the entire inner surface of the container by means such as rolling. That is difficult.

Therefore, the present inventors conducted research to find a method to uniformly and reliably coat the inner surfaces of containers with narrowed openings such as cylinders and plastic tanks, and similar objects to be coated, and as a result, the festival was completed. Rather than covering it with
A low viscosity base resin prepolymer containing no curing agent is uniformly coated on the inner surface of the container by an appropriate means, and then the curing agent is sprayed and filled into the container to cause a curing reaction.
The present invention was completed based on the discovery that the curing reaction progresses rapidly from the coated surface and that a uniform continuous coating can be easily formed on the inner surface of the container.

Here, the present invention provides coating by applying a resin material made of a polyisocyanate prepolymer containing free isocyanate groups to the inner surface of a container, and then spraying and filling the container with a curing agent made of ammonia or amine. It is characterized by causing a rapid curing reaction from the surface.
This is a method for coating the inner surface of a container.

The present invention will be explained in detail below.

The coating material used in the present invention is a catalytically cured urethane resin coating using an amine catalyst (curing agent). This paint is an industrial paint with excellent chemical resistance, solvent resistance, corrosion resistance, and abrasion resistance, and is suitable for purposes such as protecting the inner surface of containers and preventing rust.

Conventionally, this type of urethane resin paint was used for painting after mixing the base resin and amine curing agent, which are the paint film forming components, before use, but the method of the present invention allows these two components to be mixed together. Seed components are applied separately without mixing.

The base resin used in this invention is a polyhydric or polyisocyanate (generally diisocyanate) prepolymer containing free isocyanate groups. Such prepolymers are commonly used in catalyst-curing urethane resin paints and are well-known materials. Specific examples of prepolymers containing free isocyanate groups include tolylene diisocyanate (TDI), xylene diisocyanate (MDI),
), low molecular weight homopolymers of polyisocyanates such as hexamethylene diisocyanate (HDI), and polyol-added prepolymers obtained by subjecting these polyisocyanate monomers to an addition reaction with polyols such as glycols. In the case of this adduct-type prepolymer, the polyisocyanate is reacted in excess with respect to the polyol so that the isocyanate group is present at the end of the prepolymer. This reaction is well known and commercially available products of this adduct type prepolymer are also available. Examples of suitable polyols include propylene glycol, trimethylolpropane, acrylic polyols, alkyd polyols, epoxy resins, epoxy-modified acrylic polyols, and the like. Specific examples of polyisocyanate-polyol adduct type prepolymers include prepolymers of propylene glycol and TDI;
Prepolymers of trimethylolpropane and XDI, prepolymers of acrylic polyol and TDI, prepolymers of alkyd polyol and XDr, prepolymers of epoxy resin and MDI, prepolymers of epoxy-modified acrylic polyol and MDI, etc. It will be done. However, the polyisocyanates and polyols listed here are merely examples, and the present invention is not limited thereto.

The degree of polymerization of the prepolymer is preferably adjusted so as to provide a viscosity suitable for flow coating, for example by transfer. Generally, the viscosity of the prepolymer is 10-3000 cp
s, preferably within the range of 50 to 1 QOOcps.

According to the method of the invention, this polyisocyanate prepolymer (base resin) containing free isocyanate groups is first applied to the inner surface of the container. This application may be carried out by any means as long as uniform coverage is achieved. One example of a method suitable for coating the inner surface of a container with a narrow opening is to first inject an excess amount of prepolymer into the container through the opening, then roll the container to cause the resin to flow and adhere uniformly to the inner surface. rear,
This is to discharge excess resin. Depending on the shape of the container, it may be possible to coat the inner surface by spraying the prepolymer. After uniformly coating the inner surface of the container with the prepolymer base resin,
A gaseous or liquid curing agent is sprayed into the container to fill it, and the prepolymer coating formed on the inner surface of the container is rapidly hardened from the surface.

The curing agent used in the present invention is selected from ammonia and amines, in particular dimethylethanolamine (DMEA>
Tertiary amines such as , tetramethylethylenediamine (TMEDA) are preferred, but other amines and ammonia are also effective as curing agents.

The sprayed curing agent remains in the container for an appropriate amount of time (e.g. 1 to 30 minutes) so that the entire container is sufficiently filled and the desired curing reaction proceeds, and then the remaining curing agent is drained from the container. let Thereafter, when the container is left in the air, the free isocyanate groups in the base resin react with moisture in the air, the curing reaction further progresses, and a cured film is obtained. The time required to form a cured film is generally within 2 hours, for example 10 to 20 minutes, from the time the curing agent is sprayed.

In the above explanation, the object to be coated was referred to as a "container" for the sake of simplicity. However, as is clear from the above explanation, the method of the present invention applies only to containers such as tanks and cylinders. Objects to be coated, such as similar-shaped articles used for purposes other than containers, or curved pipes such as small-diameter corrugated pipes, which may result in uneven coating or uncoated surfaces using conventional spray methods. It can be similarly applied to the inner surface coating of.

Therefore, the method of the present invention also includes within its scope the coating of the inner surface of such container-like objects or small diameter tubes.

Next, the present invention will be described using Examples, but these Examples are merely illustrative for detailed explanation of the present invention, and are not intended to limit the present invention.

Implementation man↓ Acrylic polyol and TDI were mixed at room temperature for 15 minutes using a conventional method.
A prepolymer having a viscosity of 80 cps was prepared by reacting for a minute and was used as a base resin. This resin material is
High pressure gas container (for 7n?) compliant with S B-8241
A surplus amount of the compound was injected into a steel cylinder, and the cylinder was rolled to coat the inner surface of the cylinder uniformly, and the remainder was discharged from the cylinder. next,
DMEA was used as a curing agent, and the amount of amine in the air was 1500.
A mist was sprayed into the cylinder in an amount of ppm, the cylinder was filled with water, and left for 10 minutes. Thereafter, the remaining curing agent liquid was drained and the product was left at room temperature. After 30 minutes, the coating was completely cured, forming a uniform inner coating with a thickness of 55 microns.

On the other hand, for comparison, using a prepolymer made of acrylic polyol and TDI mixed with a DMEA curing agent in advance, the airless spray method and the container The interior was painted by injecting paint inside and transferring it. This comparative prepolymer had a high viscosity of 5000 cps.

As a result, with the airless spray method, paint was left unpainted in the blind spot of the spray pattern at the bottom of the neck of the container, and even with the latter method, because the viscosity was as high as 5,000 cps, the paint spread only on a portion of the inner surface. However, a uniform coating film could not be obtained in either case.

A prepolymer having a viscosity of 95 cps was prepared by reacting an epoxy resin with XDI for 12 minutes at room temperature using a conventional method, and used as a base resin. An excess amount of this resin material was injected into a polyethylene tank having a capacity of 2 On, the tank was rolled to uniformly coat the inner surface, and the remainder was discharged. Next, TMEDA was sprayed into the tank as a curing agent in an amount such that the amount of amine in the air was 1500 ppm to fill the tank, and the tank was left as it was for 15 minutes to allow the curing reaction by the amine curing agent to proceed. Ta. Thereafter, the curing agent liquid remaining in the tank was drained and the tank was left at room temperature. After 40 minutes, the coating film was completely cured, and a uniform inner coating film with a thickness of 45 μm was formed.

On the other hand, for comparison, a prepolymer consisting of an epoxy resin and MDI in which a TMEDA curing agent had been mixed in advance was used in the same polyethylene tank as described above, using the airless spray method and the injection/transfer method described above. The inner surface was painted. The viscosity of this comparative prepolymer was 3500 cps. As a result, with the airless spray method, the area around the opening edge of the tank could not be coated uniformly, and the injection and
In the transfer method, the fluidity was poor due to the high viscosity of 3500 cps, and complete coating was impossible.

As is clear from the above description, the method of coating the inner surface of a container according to the present invention is effective for coating containers with narrowed openings such as tanks and bongs, and bent tubes such as small-diameter corkscrews, etc., which can be coated unevenly using the conventional spray method. It is very useful in that it can easily form a uniform and reliable coating film on the inner surface of the object to be coated, where uncoated areas would otherwise occur. In addition, conventional catalytic curing urethane resin paints have a limited pot life and are difficult to adjust, making it difficult to use, but the present invention eliminates these concerns. One of the advantages is that there is no such thing.

Applicant: Sumitomo Metal Industries, Ltd. Agent Patent Attorney Akira Hirose -

Claims (1)

[Claims] After applying a resin material made of a polyisocyanate prepolymer containing free isocyanate groups to the inner surface of a container or i-tube, a hardening agent consisting of ammonia or amine is sprayed into the container or tube to fill the coating. A method for coating the inner surface of a container or small-diameter pipe body, which is characterized by causing a rapid curing reaction from the surface.