JP2000336304A - Metacresol resin composition for coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin for a coating material for a can, having extremely superior fast curability compared to a conventional phenol resin for the coating for the can, and capable of providing a coated film having small potassium permanganate consumption and excellent in processability such as bending. SOLUTION: This metacresol resin composition for a coating material is a reaction product obtained by reacting a prepolymer obtained by reacting metacresol with formaldehydes, with alcohols, having 600-1,800 weight average molecular weight (Mw), and <=3.0 ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), and containing >=60% of alkoxylated methylol group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a meta-cresol resin composition for coatings useful as a curing agent for inner coatings of epoxy cans and the like. The present invention relates to a meta-cresol resin composition for paints that consumes a small amount and has excellent workability such as bending.

[0002]

2. Description of the Related Art As is well known, the performance of an epoxy resin-phenolic resin paint is greatly affected by the properties of the phenolic resin to be blended. Actually, the balance of performance such as curability, hygiene, adhesion, workability, etc. is changed depending on the type and composition ratio of the phenol component used, the ratio of epoxy resin / phenol resin, etc. Phenolic resin is used.

In recent years, phenol resins, which are curing agents for epoxy-based paints, have been required to have rapid curability. Generally, the baking of paint for cans is 150-
It is performed at 300 ° C. for about 30 seconds to 20 minutes. However, such high-temperature baking requires a large amount of heat energy cost and generates fumes and tar at high temperatures. In addition, there is a demand for a curing agent resin that cures in a short time.

However, the conventional phenolic resins for coatings containing a difunctional phenol as a main component have a weight average molecular weight of 400 to 800, a relatively low molecular weight, and a large amount of low molecular weight components. When used as a curing agent for paint on the inner surface of a can, there is a problem that curability is low and potassium permanganate consumption is high. In order to solve these characteristics, there is also an example of using a high-molecular-weight resol type phenol resin using trifunctional phenols or bisphenol A. However, since the methylol group concentration becomes high, self-condensation with a curing agent alone is performed. There is also a disadvantage that the tendency is increased and processability is poor. Furthermore, bisphenol A
Is suspected as an endocrine disrupting substance, and it is not preferable to use it as a curing agent for paint on the inner surface of cans.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a curing agent for an epoxy can inner coating which has a short curing property and consumes potassium permanganate in a coating film to be formed. It is an object of the present invention to provide a meta-cresol resin composition for coatings, which is small in size and excellent in processability. As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that a metacresol resin having a specific molecular weight, which has a narrow molecular weight distribution and an extremely large degree of alkoxylation, is preferable.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a reaction product obtained by reacting a prepolymer obtained by reacting metacresol with formaldehyde and an alcohol, and comprising a weight average molecular weight ( Mw) is 600 to 1,800, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 3.0 or less, and 60% or more of the methylol groups are alkoxylated. The present invention relates to a meta-cresol resin composition for paints.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. In order to obtain the meta-cresol resin composition for a paint of the present invention, for example, a method including the following three steps can be mentioned. In the first step, formaldehyde is added to meta-cresol to form methylol, in the second step, dehydration-condensation of the methylolated meta-cresol proceeds to form a prepolymer, and in the third step, the prepolymer reacts with alcohols to form an alkoxy group. It is a method to become.

In the first step, the reaction between metacresol and formaldehyde is carried out in the presence of a basic catalyst. Here, it is preferable to react all of the used meta-cresol to form methylol. In the first step, dehydration condensation of methylolated metacresols may be partially performed in addition to methylolation of metacresol.

Formaldehyde used in the first step includes formalin, paraformaldehyde and the like. The amount of formaldehyde used is 2.0 to 2.0 mol in terms of formaldehyde per mol of metacresol.
5.0 mol is preferable, and 3.0 to 4.0 mol is more preferable. When the amount of formaldehyde used (molar ratio) is less than 2.0 mol, non-methylolated meta-cresol often remains, while when it exceeds 5.0 mol, the methylol group concentration in the resin tends to be too high. There is.

As the basic catalyst used in the first step, a known catalyst used in synthesizing a general resol type phenol resin can be used. For example, hydroxides of alkali metals such as sodium hydroxide, lithium hydroxide and potassium hydroxide, hydroxides of alkaline earth metals such as magnesium hydroxide and calcium hydroxide, amines such as triethylamine, trimethylamine and ethanolamine Kind. The use amount of the basic catalyst is preferably 0.01 to 0.3 mol per 1 mol of metacresol. 0.
If the amount is less than 01 mol, the methylolation reaction is slow and the productivity is lowered, and if it exceeds 0.3 mol, the reaction is too fast to control.

The reaction conditions in the first step are preferably such that the reaction temperature is 40 to 55 ° C. and the reaction time is about 0.5 to 3 hours. The important point in the first step is to convert all of meta-cresol to methylol. To this end, the reaction temperature should be as low as possible. However, if the temperature is lower than 40 ° C., the reaction is slow and the productivity is reduced.

In the second step, the methylolated metacresols obtained in the first step are subjected to dehydration condensation at a reaction temperature of 60 ° C. or more to form a prepolymer. The degree of prepolymerization is controlled by the molecular weight of the resulting prepolymer. The weight average molecular weight at this time is preferably from 300 to 1,000, and more preferably from 400 to 800. If the weight average molecular weight is out of the range of 300 to 1,000, it becomes difficult to control the alkoxylation in the third step.

The reaction conditions in the second step may be a reaction temperature of 60 to 80 ° C. and a reaction time of about 1.0 to 3 hours. After completion of the prepolymer reaction, the used basic catalyst is neutralized with a known acid such as sulfuric acid, acetic acid, phosphoric acid, etc., washed with water, and concentrated under reduced pressure to remove water.

In the third step, the prepolymer obtained in the second step is reacted with an alcohol in the presence of an acidic catalyst to carry out alkoxylation of the prepolymer.

As the acidic catalyst used in the third step, generally known catalysts such as oxalic acid, formic acid and acetic acid can be used, and the amount thereof is 0.1 to 1 mol of meta-cresol.
About 01 to 0.1 mol, preferably 0.03 to 0.007
It is good to be about mol.

The alcohols used in the third step include n-butyl alcohol, isobutyl alcohol, n-amyl alcohol and the like. An important point in the third step is to alkoxylate at least 60% of the methylol groups, and it is necessary to mix alcohols in equal amounts or more. The blending amount of the alcohol with respect to the prepolymer is preferably 100 to 400 PHR, more preferably 150 to 300 PHR. If it is lower than 100 PHR, the alkoxylation of the methylol group becomes insufficient, and if it is higher than 400 PHR, the productivity decreases.

The reaction conditions are as follows:
The reaction may be performed at 0 ° C. for about 3 to 20 hours while removing the condensed water.

By carrying out the first, second and third steps, the weight average molecular weight (Mw) is from 600 to 1,800 and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw / Mn) is 3.0 or less, and 60
% Or more can be obtained.

The meta-cresol resin composition for paints of the present invention is obtained as described above, and has a weight average molecular weight (M
w) is from 600 to 1,800, preferably from 800 to 1,5
00 and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 3.0 or less, preferably 2.0 or less, and 60% or more, preferably 70% of the methylol group. The above is what has been alkoxylated.
When the meta-cresol resin composition for a paint of the present invention is used as a curing agent for an inner paint of an epoxy can, it has a short-time curability, and the formed coating film consumes a small amount of potassium permanganate, and has a bending property. It has extremely excellent performance in processability. If the weight average molecular weight is less than 600, the curability and the consumption of potassium permanganate deteriorate, while if the weight average molecular weight exceeds 1,800, the processability tends to deteriorate. 2. The ratio of the weight average molecular weight to the number average molecular weight is 3.
If it exceeds 0, the consumption of potassium permanganate increases due to the influence of the low molecular weight component, and the processability deteriorates due to the effect of the high molecular weight component. If the degree of alkoxylation is less than 60%, the tendency of self-condensation is increased, so that the processability is extremely reduced.

The weight average molecular weight and the ratio of the weight average molecular weight to the number average molecular weight are determined by gel permeation chromatography (GPC) in terms of polystyrene, and the degree of alkoxylation is determined by NMR.

The meta-cresol resin composition for a paint of the present invention exhibits particularly excellent performance as a curing agent for an epoxy-based paint, but has an acrylic or alkyd type having a hydroxyl group.
Excellent performance as a curing agent such as polyester. The meta-cresol resin composition for a paint of the present invention can be used not only for an organic solvent type paint but also for a water-based paint.

[0022]

The present invention will be described below with reference to examples. However, the present invention is not limited by these examples.

Example 1 Metacresol 108. was placed in a 1 L four-necked flask equipped with a stirrer, heat exchanger and thermometer.
0 g (1 mol), 324 g (3 mol) of 37% formalin
And a 25% aqueous sodium hydroxide solution 16 as a catalyst.
g (0.1 mol) at 50 ° C. for 3 hours, then 70
The reaction was carried out at 3 ° C. for 3 hours. After completion of the reaction, 50% sulfuric acid aqueous solution was added for neutralization, and the separated and precipitated resin was washed four times with water. Further, after water was removed by dehydration under reduced pressure, 400 parts of n-butanol was added to 100 parts of the produced prepolymer having a weight average molecular weight of 800, 0.05 mol of formic acid was added as a catalyst, and the mixture was reacted at 100 ° C. for 10 hours. I let it. Further, the target 50% meta-cresol resin varnish 3 is obtained by concentration under reduced pressure.
00 parts were obtained. The weight average molecular weight of the product by GPC was 1,000, and the ratio of the weight average molecular weight to the number average molecular weight was 1.
5. The degree of alkoxylation by NMR was 80%.

Example 2 108.0 g (1 mol) of meta-cresol and 432 g (4 mol) of 37% formalin were added to the same reactor as in Example 1, and 40 g (0.4 mol) of triethylamine was added as a catalyst. 3 hours at 50 ° C
Then, the reaction was carried out at 70 ° C. for 4 hours. After completion of the reaction, formic acid was added for neutralization, and the separated and precipitated resin was washed four times with water. Further, after water was removed by dehydration under reduced pressure, 200 parts of n-butanol was added to 100 parts of the produced prepolymer having a weight average molecular weight of 600, and 0.03 mol of formic acid was added as a catalyst, followed by a reaction at 100 ° C. for 6 hours. I let it. Further, the target 50% meta-cresol resin varnish 28 is concentrated by vacuum concentration.
0 parts were obtained. The weight average molecular weight of the product by GPC was 7
00, the ratio of the weight average molecular weight to the number average molecular weight is 1.7, N
The degree of alkoxylation by MR was 75%.

Example 3 108.0 g (1 mol) of metacresol, 188 g of 80% paraformaldehyde (5 mol as formaldehyde) and 200 g of water were added to the same reaction apparatus as in Example 1, and 25% of water was used as a catalyst. Add 64 g (0.4 mol) of aqueous sodium solution and add
The reaction was allowed to proceed for 2 hours at 80 ° C. After completion of the reaction, acetic acid was added for neutralization, and the separated and precipitated resin was washed four times with water. Further, after removing water by dehydration under reduced pressure, 150 parts of n-amyl alcohol was added to 100 parts of the produced prepolymer having a weight average molecular weight of 1,000, and 0.03 mol of acetic acid was added as a catalyst. The reaction was performed for 10 hours. Furthermore, 310 parts of the target 50% meta-cresol resin varnish was obtained by vacuum concentration. The weight average molecular weight of the product by GPC was 1,400, the ratio of the weight average molecular weight to the number average molecular weight was 2.0, and the degree of alkoxylation by NMR was 7
It was 0%.

Comparative Example 1 108.0 g (1 mol) of metacresol and 324 g (3 mol) of 37% formalin were added to the same reactor as in Example 1, and 1.6 g of a 25% aqueous sodium hydroxide solution as a catalyst ( (0.01 mol) was added and reacted at 50 ° C. for 3 hours and then at 70 ° C. for 3 hours. After the completion of the reaction, a 50% aqueous sulfuric acid solution was added for neutralization, and the separated and precipitated resin was washed three times with water. Further, after removing water by dehydration under reduced pressure, 80 parts of n-butanol was added to 100 parts of the produced prepolymer having a weight average molecular weight of 600, 0.05 mol of formic acid was added as a catalyst, and the reaction was carried out at 100 ° C. for 10 hours. I let it. Furthermore, 220 parts of a 50% meta-cresol resin varnish was obtained by vacuum concentration. The product had a weight average molecular weight by GPC of 1,400, a ratio of the weight average molecular weight to the number average molecular weight of 3.2, and a degree of alkoxylation by NMR of 65.
%Met.

Comparative Example 2 108.0 g (1 mol) of meta-cresol and 432 g (4 mol) of 37% formalin were added to the same reactor as in Example 1, and 25% sodium hydroxide was used as a catalyst. 3.2 g of aqueous solution (0.
02 mol) at 50 ° C. for 3 hours and then at 70 ° C. for 2 hours.
Allowed to react for hours. After the completion of the reaction, a 50% aqueous sulfuric acid solution was added for neutralization, and the separated and precipitated resin was washed three times with water. Furthermore, after removing water by dehydration under reduced pressure, the resulting weight average molecular weight 7
150 parts of n-butanol was added to 100 parts of the prepolymer No. 00 and reacted at 100 ° C. for 2 hours. Furthermore,
50% meta-cresol resin varnish 240 by concentration under reduced pressure
Got a part. The weight average molecular weight of the product by GPC is 90.
0, ratio of weight average molecular weight to number average molecular weight is 1.8, NM
The degree of alkoxylation by R was 30%.

Comparative Example 3 In the same reactor as in Example 1, 75.6 g (0.7 mol) of paracresol, 32.4 g (0.3 mol) of metacresol, and 24% of 37% formalin 24
3 g (3 mol) was added, and 48 g (0.3 mol) of a 25% aqueous sodium hydroxide solution was added as a catalyst, followed by reaction at 50 ° C. for 3 hours and then at 80 ° C. for 1 hour. 25 after reaction
% Sulfuric acid aqueous solution to neutralize and separate and precipitate the resin.
Washed twice. Further, after water was removed by dehydration under reduced pressure, 150 parts of n-butanol was added to 100 parts of the produced prepolymer having a weight average molecular weight of 700, and reacted at 100 ° C. for 7 hours. Further, 200 parts of a 50% cresol resin varnish was obtained by concentration under reduced pressure. The product has a weight average molecular weight by GPC of 1,300, a ratio of the weight average molecular weight to the number average molecular weight of 1.8, and a degree of alkoxylation by NMR of 70%.
Met.

[Coating film performance test] Using the cresol resins obtained in Examples 1 to 3 and Comparative Examples 1 to 3, coating materials were prepared as follows, and the coating materials were applied to an aluminum plate and baked. , And tests for workability, potassium permanganate consumption, and adhesion were conducted. Various test methods are shown below, and the test results are shown in Table 1.

1. Preparation of Paint 30 parts of Epicoat 1009 (epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd.) was dissolved in a mixed solvent of 50 parts of butyl cellosolve and 50 parts of xylene to obtain an epoxy resin solution having a solid content of 30%. The epoxy resin solution was mixed with the cresol resins obtained in Examples 1 to 3 and Comparative Examples 1 to 3 so that the weight ratio of the solid content was 9: 1 to obtain a test paint.

2. Coating performance test method Each coating prepared by the above method was applied to a 0.3 mm aluminum plate (5052 material) with a bar coater so as to have a dry coating thickness of 5 to 7 μm, and baked at 240 ° C. for 2 minutes. went. And the following coating film performance was measured. (1) Sol fraction The coated aluminum plate was cut into a predetermined size, extracted at the boiling point of methyl ethyl ketone for 1 hour, and the ratio of the uncured component (sol component) was determined from the weight difference before and after extraction and the coating film weight. (2) Potassium permanganate consumption Using 1 ml of ion-exchanged water per 1 cm ^{2 of the} coating film, 130
A retort extraction was performed at 30 ° C. for 30 minutes, and the obtained test liquid was measured according to the measurement method described in the Food Sanitation Law (Ministry of Health and Welfare No. 434). (3) Workability A test piece obtained by cutting a painted aluminum plate to 3 cm x 5 cm is preliminarily bent so that the painted surface is on the outside, and three aluminum plates having the same thickness as the test piece are inserted as spacers, and then 3 kg. Was dropped from a height of 30 cm to perform bending. The bent part of this bending test piece is immersed in 1% saline solution, and the test piece is +
Current value when a 6V DC load is applied as a pole (mA)
Was read and evaluated.

3. Test results

[Table 1]

[0033]

When the meta-cresol resin composition for a paint of the present invention is used as a curing agent for an inner paint of an epoxy can or the like, it has a short-time curing property, and the formed coating film is potassium permanganate. Since it has low consumption and excellent workability, it can be suitably used as a curing agent for paints on the inner surface of metal cans such as cans for storing foods and the like and beverage cans.

Claims (1)

[Claims] 1. A reaction product obtained by reacting a prepolymer obtained by reacting meta-cresol with formaldehyde with an alcohol, and having a weight average molecular weight (Mw) of 600 to 1,80.
0, weight average molecular weight (Mw) and number average molecular weight (M
A meta-cresol resin composition for paints, wherein the ratio (Mw / Mn) of n) is 3.0 or less and 60% or more of the methylol groups are alkoxylated.