JP2002249532A - Cresol novolak resin for coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cresol novolak resin having a narrow molecular weight distribution and a reduced amount of a binucleate component which can form a coating film having excellent curability when used as the curing agent for epoxy resin based coating materials. SOLUTION: The cresol novolak resin composition for coating materials is obtained by reacting cresols composed of o-cresol and p-cresol with formaldehyde in the presence of an acidic catalyst, and has a bonding ratio of the o- cresol to the p-cresol in the resin, obtained by the NMR measurement, of 1/9 to 7/3, a bonding molar number of the formaldehyde per mole cresol component of 0.7-0.95 mole, a content of a binuleate component, obtained by the GPC measurement, of <=6%, a number average molecular weight of 600-3,000 and, simultaneously, a degree of dispersion (a ratio of the weight average molecular weight to the number average molecular weight) of <=3.2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cresol novolak resin having a low binuclear component content and a narrow molecular weight distribution. The cresol novolak resin of the present invention is particularly suitably used as a curing agent for an epoxy resin-based food can coating.

[0002]

2. Description of the Related Art Cresol novolak resins obtained by subjecting cresols and formaldehyde to a dehydration condensation reaction in the presence of an acidic catalyst are well known, and meta- and para-cresols obtained by using meta-para-cresol as the cresols are known. Paracresol novolak resins are widely used as curing agents for epoxy resins, binders for positive photoresists, and the like. Examples of the use of the cresol novolak resin as a curing agent for an epoxy resin include paints for food cans, adhesives, molding materials, and laminates that require heat resistance.

A conventionally known meta-paracresol novolak resin has a number average molecular weight of 500 to 1500.
Having a dispersity of 4.0 to 18.0 and a cresol binuclear component content of 6 to 20%. In an epoxy resin material using such a cresol novolak resin as a curing agent, the reactivity between the cresol binuclear component and the epoxy resin is low, so that the higher the content of the cresol binuclear component, the higher the heat resistance and curability. There is a disadvantage that it is inferior.

Next, an epoxy resin-based paint for food cans will be described. Food can paint is a protective paint that is coated on the inner surface of a metal can to prevent corrosion of the metal can made of tin, tin-free steel, aluminum, etc. and elution of the metal into the contents. It is manufactured by dissolving an epoxy resin and a curing agent in a solvent such as xylene or butyl cellosolve.

[0005] As a paint for food cans, an epoxy resin-based paint containing a resol-type cresol resin as a curing agent is usually used because of its excellent adhesion and corrosion resistance. In addition, the cured coating film formed using these paints has a workability and adhesion that can withstand the canning process, heat resistance that can withstand retort sterilization, and low elution of components from the coating film to the contents of the can. In addition, a cresol resin as a curing agent has been studied in various ways as well as a base resin such as an epoxy resin.

When a resol type cresol resin is used as a curing agent for an epoxy resin, the self-condensation of the resole resins also occurs during curing, so that the coating film becomes hard and is inferior in workability in canning and in corrosion resistance of the coating film. Because of this aspect, the use of a novolak-type cresol resin having no tendency to self-condensation is expected to improve such disadvantages.

However, when a conventionally known cresol novolak resin is applied as a curing agent for an epoxy resin can coating, a large amount of a cresol binuclear component having low reactivity with the epoxy resin remains. Curing is slow, and the resulting coating film is inferior in heat resistance and hygiene. For this reason, it is desired to reduce the content of the binuclear component in the cresol novolak resin.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a hardening agent for an epoxy resin-based coating composition which can form a coating film having excellent curability, has a narrow molecular weight distribution and contains a binuclear component. It is to provide a cresol novolak resin in a small amount.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a cresol novolak resin obtained by reacting cresols consisting of orthocresol and paracresol with formaldehyde in the presence of an acidic catalyst. The binding ratio of ortho-cresol to para-cresol in the resin is 1/9 to 7/3, and the number of moles of formaldehyde bonded to 1 mole of the cresol component is 0.7.
0.95 mol, the content of the binuclear component determined by the GPC measurement method is 6% or less, and the number average molecular weight is 60%.
A cresol novolak resin for paint, wherein the cresol novolak resin has a dispersion of from 0 to 3000 and a dispersity of 3.2 or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. The cresol novolak resin of the present invention is a novolak resin obtained by reacting cresols consisting of orthocresol and paracresol with aldehydes in the presence of an acidic catalyst, and a binding ratio of orthocresol to paracresol in the resin. Is 1/9 to 7/3. If it is less than 1/9, the compatibility with the epoxy resin is reduced, so that the curability and hygiene are reduced. On the other hand, if it exceeds 7/3, the melting point will be low and the heat resistance will be reduced.

Here, the binding ratio of ortho-cresol to para-cresol is 13% of cresol novolak resin.
A C-NMR (nuclear magnetic resonance spectrum) measurement was performed to find a peak at 21.5 ppm based on the methyl group of paracresol and a peak of 16.5 ppm based on the methyl group of orthocresol.
Is obtained from the area intensity ratio of the peaks. 13C-
The NMR measurement apparatus and measurement conditions are as shown below.
NMR spectrometer: JNM-AL300 manufactured by JEOL Ltd., pulse sequence: non-NOE method, repetition time: 10 seconds, number of accumulation: 3000 times, solvent: 1,4-dioxane / deuterated methanol = 6/1 (solid content: 15%) Adjusted to become

Further, the number of moles of formaldehyde bonded to 1 mole of the cresol component of the cresol novolak resin of the present invention is 0.7 to 0.95 mole. If it is less than 0.7 mol, the content of the binuclear component is increased or the number average molecular weight is reduced, so that the curability and hygiene are reduced.
On the other hand, if it exceeds 0.95 mol, the molecular weight becomes too high, so that the compatibility with the epoxy resin decreases.

Here, the binding ratio of formaldehyde to cresol component is 1H of cresol novolak resin.
-NMR (nuclear magnetic resonance spectroscopy) measurement was performed, and a peak of 1.5 ppm based on a methyl group in a cresol component obtained by combining ortho-cresol and para-cresol, and a peak based on a methylene group formed by addition condensation of cresol with formaldehyde were measured. It is obtained from the area intensity ratio of the peak at .75 ppm. The 1H-NMR measurement apparatus and measurement conditions are as shown below. NMR spectrometer: JEOL J
NM-AL300, pulse sequence: NON method, repetition time: 7 seconds, integration frequency: 16 times, solvent: heavy acetone (adjusted to a solid concentration of 15%)

The cresol novolak resin of the present invention has a G
6% cresol binuclear content determined by the PC measurement method
It is as follows. In order to determine the content of the cresol binuclear component by the GPC measurement method, based on the GPC measurement chart,
It is calculated from the area ratio (%) of the portion corresponding to the cresol binuclear component to the whole resin. If this content exceeds 6%, the curability is reduced, and the heat resistance and hygiene of the coating film are reduced. The cresol novolak resin of the present invention has a number average molecular weight of 600 to 3000. If the number average molecular weight is less than 600, the heat resistance and hygiene of the cured coating film will be reduced, and if the number average molecular weight exceeds 3000, the compatibility with the epoxy resin will be poor.

The cresol novolak resin of the present invention has a degree of dispersion of 3.2 or less. If the degree of dispersion exceeds 3.2, the low molecular weight component in the resin increases and the sanitary property of the cured coating decreases, and / or the high molecular weight component in the resin decreases the workability of the cured coating. May be invited. Here, the degree of dispersion is a ratio of weight average molecular weight / number average molecular weight. In the present invention, the weight average molecular weight and the number average molecular weight are determined by GPC (gel permeation chromatography). A calibration curve prepared using a polystyrene standard substance was used. GP
C measurement uses tetrahydrofuran as an elution solvent,
The measurement was performed under the conditions of a flow rate of 1.0 ml / min and a column temperature of 40 ° C. The apparatus is composed of a main body: TOSOH HLC-8020, and a detector: TOSOH UV-wave set at 280 nm.
8011, analytical column: SHOdex K manufactured by Showa Denko
One F-802, One KF-803, KF-805
One was used.

The cresol novolak resin of the present invention can be produced, for example, as follows. Orthocresol 10-80 mol%, paracresol 20-90
0.75 to 2.0 mol of formaldehyde is reacted with 1 mol of cresol consisting of mol% in the presence of an acidic catalyst (reaction step), and after the reaction is completed, dehydration and demonomerization are performed under normal pressure and reduced pressure (dehydration). Process). In the reaction step, by using the ratio of orthocresol, paracresol and formaldehyde within the above range,
A desired cresol novolak resin having an area ratio of the binuclear component of 6% or less, a number average molecular weight of 600 to 3000, and a dispersity of 3.2 or less can be obtained.

The reason that the content of the binuclear component in the cresol novolak resin of the present invention can be reduced is that ortho-paracresol has a small difference in reactivity with formaldehyde, and therefore, the low-molecular-weight component of cresol which is insufficiently reacted. This is probably due to the difficulty of remaining. On the other hand, in the case of meta-paracresol, which has been conventionally used, meta-cresol has a very high reactivity, so that para-cresol hardly reacts with formaldehyde. As a result, low molecular components such as binucleate are contained. It is expected that the amount will be large. Also,
Since paracresol has high crystallinity, when used alone, there is a property that the reaction with formaldehyde does not easily proceed,
When orthocresol is used alone, the content of the binuclear component decreases, but the curability when used as a curing agent becomes insufficient. For these reasons, by using ortho-cresol and para-cresol at an appropriate mixing ratio, a cresol novolak resin having a low content of binuclear components and excellent curability when used as a curing agent is obtained. You can do it.

As formaldehyde, either formalin (aqueous solution) or paraformaldehyde (solid) may be used, but paraformaldehyde is preferred for obtaining a resin having a narrow molecular weight distribution. As the acidic catalyst,
Organic acids such as p-toluenesulfonic acid and oxalic acid, sulfuric acid,
Mineral acids such as hydrochloric acid and the like that are usually used in the production of phenol novolak resins can be used.
0.1 to 2 parts by weight is preferable for 100 parts by weight of cresols.

The reaction conditions are not particularly limited, but a reaction temperature of 60 to 100 ° C. and a reaction time of 2 to 5 hours are preferable. Further, a reaction solvent can be used if necessary. After completion of the reaction, dehydration and demonomerization are performed under normal pressure and reduced pressure to obtain a cresol novolak resin for an epoxy resin curing agent. The conditions for dehydration and demonomerization are not particularly limited, but in consideration of the properties of the obtained cresol novolak resin, the degree of reduced pressure is 0.1 to 60 t.
It is preferably performed at about orr, and the final demonomerization temperature is preferably performed at 150 to 250 ° C.

[0020]

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

Example 1 Orthocresol 216 was placed in a 3 L four-necked flask equipped with a stirrer, heat exchanger and thermometer.
g (2 mol), 864 g (8 mol) of paracresol, 8
337.5 g (9 mol) of 0% paraformaldehyde was added, and 2 parts by weight of oxalic acid was charged as a catalyst with respect to 100 parts of cresols, and the reaction was carried out at 100 ° C. for 4 hours. After that, it was dehydrated under normal pressure to an internal temperature of 150 ° C.
Dehydration and demonomerization were performed at an internal temperature of 220 ° C. under a reduced pressure of orr to obtain 1185 g of a cresol novolak resin. In the obtained resin, the binding ratio of ortho-cresol to para-cresol was 1.7 / 8.3, the binding ratio of formaldehyde to 1 mole of the cresol component was 0.88, the number average molecular weight was 1233, the dispersity was 2.4, and the free monomer was 0. .7
%, Binucleate component was 3.2%.

<< Examples 2 to 5, Comparative Examples 1 to 4 >> Cresol novolak resins were produced in the same manner as in Example 1 with the formulations shown in Table 1. The physical properties of the obtained cresol novolak resin are also shown in Table 1.

[Coating film performance test] Using the cresol novolak resin obtained in each of Examples 1 to 5 and Comparative Examples 1 to 4, a coating material was prepared as follows, and the coating material was applied to an aluminum plate and baked. The treatment was performed, and tests for curability, heat resistance (retort resistance), hygiene (consumption of potassium permanganate), and workability were performed. Various test methods are shown below, and the test results are shown in Table 2.

1. Preparation of paint Epicoat 1009 (epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd.) was dissolved in a mixed solution of xylene and butyl cellosolve 1/1 to obtain an epoxy resin solution having a solid content of 25%. The epoxy resin solution and the cresol novolak resins obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were mixed and dissolved so that the weight ratio of the solid components was 8: 2, and the total solid components of both components were further dissolved. 0.2 part of phosphoric acid is added to 100 parts of
A variety of paints were obtained.

2. Coating film performance test method Each paint 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 of 5 to 7 μm, and was baked at 200 ° C. for 10 minutes. went. And the coating film performance shown below was measured.

(1) Curability A test piece having a coating film area of 100 cm ² was subjected to a solvent extraction treatment under reflux of 100 ml of methyl ethyl ketone for 1 hour, and the weight (%) of the remaining coating film after the treatment relative to the weight of the coating film before the treatment was determined. evaluated. ：: 100 to 90% △: 89 to 80% ×: 79% or less

(2) Heat resistance The test piece was immersed in water, and the whitening state of the coating film that had been retorted at 130 ° C. for 30 minutes was visually judged. ：: No whitening Δ: Slight whitening ×: Significant whitening

(3) Hygiene A test piece having a coating area of 100 cm ² was immersed in 100 ml of ion-exchanged water and subjected to retort extraction at 130 ° C. for 30 minutes. Potassium permanganate consumption was measured according to (Ministry of Health and Welfare No. 434) and evaluated according to the following criteria. ：: consumption is less than 5 ppm △: 10 p at 5 ppm or more
Less than pm ×: 10 ppm or more

(4) Workability A test piece obtained by cutting a coated aluminum plate into a size of 3 cm × 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. Then, a 3 kg iron block was dropped from a height of 30 cm and bent. The current value (mA) when a current was applied for 4 seconds at an applied voltage of 6 V to the bent portion (between the resin-coated surface and the back side of the base aluminum plate) of the bent test piece was read and evaluated. ：: Current value less than 5 mA Δ: 5 mA or more and less than 10 mA ×: 10 mA or more

3. Test results

[Table 1]

[0031]

[Table 2]

The cresol novolak resin obtained in each of Examples 1 to 5 has a binding ratio of orthocresol to paracresol, a mole number of formaldehyde to 1 mole of cresol component, a binuclear component content, a number average molecular weight, and a dispersion. Each of the degrees was within an appropriate range, and good results were obtained with respect to the curability, heat resistance, hygiene, and processability of the coating film of the epoxy resin-based paint when these were used as a curing agent. On the other hand, in Comparative Example 1, since only para-cresol was used as cresols, the number average molecular weight of the obtained resin was low and the content of the binuclear component was large, so that the curability, heat resistance and hygiene of the coating film were reduced. did. Also in Comparative Example 2, since the amount of formaldehyde was small, the number average molecular weight of the resin was low and the content of the binuclear component was large, and satisfactory results were obtained in the curability, heat resistance and hygiene of the coating film. Did not. In Comparative Example 3, since only orthocresol was used as the cresol, the curability of the resin was poor, and the hygiene and heat resistance were deteriorated. Comparative Example 4 is a meta-para-cresol novolak resin. However, since the resin has a high degree of dispersion and a high binuclear component content, the curability and sanitary properties of the coating film are reduced, and the processability is poor. That was enough.

[0033]

According to the present invention, the content of the binuclear component determined by the GPC method is 6% or less, and the number average molecular weight is 60%.
It is a cresol novolak resin having a dispersity of 0 to 3000 and a dispersity of 3.2 or less, and is used as a curing agent for an epoxy resin-based paint for coating the inner surface of food cans and beverage cans, and has curability and heat resistance. In addition, a coating film having excellent hygiene can be formed.

Claims (1)

[Claims] 1. A cresol novolak resin obtained by reacting cresols consisting of ortho-cresol and para-cresol with formaldehyde in the presence of an acidic catalyst, wherein the cresol novolak resin is obtained by an NMR measurement method. Cresol binding ratio is 1/9 to 7
/ 3, and the number of moles of formaldehyde bonded to 1 mole of the cresol component is 0.7 to 0.95 mole,
A cresol novolak resin for paint, wherein the content of the binuclear component determined by GPC measurement is 6% or less, the number average molecular weight is 600 to 3000, and the dispersity is 3.2 or less.