JPH01230678A - Water-based can lining paint - Google Patents

Abstract

PURPOSE:To provide the title paint excellent in flavor, sanitariness, etc., by producing a specified self-emulsifiable resin from a purified bisphenol epoxy resin having a decreased low-MW component content and dispersing this self- emulsifiable resin in an aqueous medium. CONSTITUTION:A bisphenol-derived epoxy resin having an average MW in the range of 2000-6000 and an MW distribution is dissolved in a good solvent for this resin or molten by heating and is brought into contact with a lower alcohol to remove a component of an MW <=800 contained in the resin. The obtained purified resin is partially esterified with a carboxylated acrylic resin in the presence of an esterification catalyst to produce a self-emulsifiable bisphenol-derived epoxy resin having a carboxylated acrylic resin part. This resin is dispersed in water in the presence of an amine or ammonia to produce a water-based can lining paint.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a water-based paint for the inside of a can that is extremely hygienic. More specifically, a highly hygienic can obtained by introducing a carboxyl group-containing acrylic resin moiety into a purified bisphenol-type epoxy resin with reduced or removed low molecular weight components and dispersing it in an aqueous medium in the presence of an amine or ammonia. This relates to water-based paints for internal surfaces.

(Prior technology) Conventionally, solvent-based paints (based on a combination of bistubonol-type epoxy resin and phenol resin) have been used as paints for the inside of cans.
(hereinafter referred to as epoxy/phenol paints) are widely used. This paint system has excellent adhesion to metal substrates and water resistance, and is also used for hot-back and retort-processed contents.

It is known that unreacted low molecular weight components and high boiling point solvents remain in the coating film even under normal curing conditions, which is unsatisfactory in terms of hygiene.

In addition, water-based paints based on self-emulsifying bisphenol-type epoxy resins that have been used in recent years have water resistance and better hygiene than epoxy/phenol paints, but since they are mainly composed of epoxy resins, they do not react. At present, there remains the problem that low molecular weight components remain.

As described above, among the paints used in this technical field, there is no one that is both water resistant and hygienic, which is a problem that should be improved.

(Problems to be Solved by the Invention) As a result of repeated studies on the sanitary properties of the paint on the inside of a can, the present inventors introduced carboxyl groups into purified epoxy resin and dispersed it in an aqueous medium in the presence of amine or ammonia. It was discovered that the resulting water-based paint has improved hygiene without impairing its water resistance, and based on this knowledge, the present invention was developed.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a resin in which a self-emulsifying bisphenol-type epoxy resin having a carboxyl group-containing acrylic resin moiety introduced by chemical bonding is dispersed in an aqueous medium in the presence of an amine or ammonia. In the dispersion paint, as the self-emulsifying bisphenol epoxy resin, a raw material bisphenol epoxy resin having a number average molecular weight in the range of 2,000 to 6,000 and a molecular weight distribution is used in a solution of the resin's affinity agent, or To provide a water-based paint for the inside of a can, which uses a purified bisphenol type epoxy resin obtained by heating and melting the resin and bringing it into contact with a lower alcohol to reduce or remove components with a molecular weight of 800 or less contained in the resin. be.

Any self-emulsifying bisphenol type epoxy resin used in the present invention can be used as long as it satisfies the condition that it has a carboxyl group-containing acrylic resin moiety introduced by chemical bonding. That is, the esterification reaction composition of a carboxyl group-containing acrylic resin and an epoxy resin in JP-A-55-75460;
A polymerization reaction composition of an acrylic acid- or methacrylic acid-modified epoxy resin and an acrylic monomer in JP-A-57-105418, and a carboxyl-functional graft polymer and a carboxyl-functional graft polymer in JP-A-53-1228. Polymer epoxy resin compositions and the like can be suitably used.

The raw material bisphenol type epoxy resin used in the present invention is manufactured for industrial use.

Bis(4-hydroxyphenyl) alkanes are reacted with epichlorohydrin in the presence of a strong alkali, or bis(4-hydroxyphenyl) alkanes are added to the epoxy resin produced by this method. It is obtained by a two-step polymerization process. These bisphenol-type epoxy resins are obtained as a mixture of molecules with various degrees of polymerization and have a molecular weight distribution plate, and even if the number average molecular weight is about 2000 to 6000, it contains components with a molecular weight of 800 or less. It is
As long as the above-mentioned industrial production method is used, the contamination of components with a molecular weight of 800 or less is unavoidable. The number average molecular weight of the raw material epoxy resin is preferably in the range of 2000 to 6000,
When epoxy resins with molecular weights smaller than 2000 are used as paints for the inside of cans, processability decreases, and as the molecular weight of the epoxy resin decreases, components in the low molecular weight range increase.
Even if this is washed, the remaining proportion of low molecular weight components becomes high, which is not preferable. On the other hand, if it is greater than 6,000, the viscosity of the resin solution becomes high and only a coating material with a low solid content can be obtained, which is not preferable because it becomes difficult to obtain a uniform coating film during coating.

Examples of such raw material bisphenol-type epoxy resins include 5, commonly commercially available bisphenol-type epoxy resins, and 2
For example, Epicote 1007. Epicort 1009, Epicort) 1010 (manufactured by Yuka Shell Epoxy@).

There are AER-667 and AER-669 (manufactured by Asahi Kasei Corporation).

The purified bisphenol epoxy resin of the present invention is 500 parts by weight or less per 100 parts by weight of the raw material bisphenol epoxy resin obtained for industrial use.

It can be obtained by dissolving preferably 200 parts by weight or less of an epoxy resin affinity solvent and performing solvent extraction with a lower alcohol.

Examples of epoxy resin solvents include methyl ethyl ketone,
Examples of the lower alcohols include xylene, toluene, cyclohexanone, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol motubutyl ether, etc.
Examples include methanol, ethanol, isopropanol, and butanol.

In addition, the purified bisphenol type epoxy resin of the present invention is
The epoxy resin before purification may be brought into contact with the lower alcohol in a heated and melted state at a temperature equal to or higher than its softening point to extract and remove low molecular weight substances.

In the method of using a solution of a good solvent for epoxy resin, it is necessary to select a combination of a good solvent and a lower alcohol, which is a poor solvent, which are incompatible with each other. conduct. In this extraction operation, the epoxy resin is usually separated into a parent container in the lower layer and a lower alcohol solvent in which the low molecular weight components are extracted in the upper layer, so it is sufficient to remove the upper layer.

If the low molecular weight substances are not removed to the desired extent in one extraction operation, the extraction operation can be repeated multiple times.

In the coating system of the present invention, if even higher water resistance is required, a curing agent component for the self-emulsifying bisphenol-type epoxy resin can be used in combination.

As the curing agent component, phenol resins, amino resins, etc. can be used, but it is preferable to use phenol resins in that they can improve the water resistance of the paint without degrading its sanitary properties.

Phenol resin is produced by reacting bifunctional, trifunctional, or tetrafunctional phenols such as carbolic acid, cresols, ethylphenols, other alkylphenols, or bisphenols with aldehydes such as formaldehyde and acetaldehyde in the presence of a basic catalyst. It is preferable to use an initial condensate or an alkyl etherification product obtained by reacting the same with an alcohol. By using such an initial condensate, it is possible to increase the concentration of methylol groups or alkoxylated methyl groups in the phenolic resin, and by improving the density of the baked coating film, it is possible to improve the density of the baked coating without reducing hygiene. Water resistance can be improved.

The weight ratio of the phenol resin to the self-emulsifying bisphenol epoxy resin is preferably 2 to 15% by weight, and if it is less than 2%, the phenol resin will not contribute to curing. If it exceeds 15%, the processability of the coating film decreases, which is not preferable.

The water-based paint for the inside of a can according to the present invention can be used as a paint by adding a surfactant, an antifoaming agent, etc. to improve coating properties, if necessary.

Applicable base materials include untreated steel sheets and treated steel sheets.

Metal plates such as galvanized iron plates, tin plates, and aluminum plates are suitable, and coating methods include air spray, airless spray, electrostatic spray, dip coating, roll coater coating, and electrodeposition coating. be.

The baking conditions are 2 hours at a temperature of 150°C to 230°C.
You can choose from a range of up to 30 minutes.

The present invention will be explained below with reference to examples. In the two examples, "parts" and "%" indicate "parts by weight" and "% by weight," respectively.

(Example) Example 1 [Production of purified epoxy resin (A-1)] 1) 300 parts of Epicoat 1009 (manufactured by Yuka Shell Epoxy ■) 2) Cyclohexanone 2003) Isopropanol 4001), 2) The mixture was placed in a 4-Solo flask that had been purged with nitrogen gas once, and was heated to 120° C. and dissolved over 1 hour. Next, the temperature inside the system was set to 80℃.
After that, add 2) and stir for 30 minutes, then let it stand.
When the mixture was completely separated into two layers, the upper layer of isopropanol solution was removed. moreover.

Repeat the same cleaning operation with isopropanol 5 times.
Cooled to 0°C. Next, cyclohexanone was distilled off under heating and reduced pressure, and then taken out, and further held at 80°C under reduced pressure for 10 hours, resulting in a pale yellow solid epoxy resin 24.
Got 5 copies.

The characteristic values of this purified epoxy resin are shown below together with the raw material epoxy resin (Ebicor 1009) before cleaning treatment.

Table-1 n=o n-1Mn Mn, 7Mw (2) (χ
) Epicote 1009 1.30 1.26 3700
2.30I# epoxy resin 0.28 0.1
0 4800 Measurement of the n=o component and n-1 component in the general formula of the above bisphenol type epoxy resin in the 1.98-functional poxy resin component The content of each measured component was determined for each peak by Hakel permeation chromatography. It is expressed as a percentage of the area ratio. In the above listing, the molecular weight of the n=o component is 340, and the molecular weight of the n=1 component is 62.
It is 4.

Measurement conditions equipment JASCO side type TRI ROTER column
TSK G2500H, TSK G30 manufactured by Toyo Raidatsu
00H combination column temperature, flow rate 40°C, 1 ml/min detector UVUV-254 n Production of carboxyl group-containing acrylic resin (B)〕■)
Butyl cellosolve 470 parts 2) n-butanol 3003) styrene
1004) Ethyl acrylate
1005) Methacrylic acid
1306) Benzoyl peroxide
41) and 2) were charged into a 4-flow flask purged with nitrogen gas, and 174 of the mixed solution of 3) to 6) was charged. next,
After heating to 100°C and stirring for 30 minutes, the remaining 3/4 was added dropwise over 2 hours while maintaining the temperature at 100°C.

After the dropwise addition was completed, the mixture was further stirred for 2 hours to obtain an acrylic resin solution with a solid content of 30.5%.

[Manufacture of phenolic resin (C-1)] 1) 80 parts of ion-exchanged water 2) 2
1.5% sodium hydroxide aqueous solution 723) Bisphenol A 1404) 37% formalin
4005) 20% hydrochloric acid
706) n-butanol
1801) to 4) were charged into a 4-Solo flask purged with nitrogen gas, and reacted at 50°C for 2 hours and at 70°C for 1 hour to obtain a reddish-brown transparent solution. Cool to 40℃.

When 5) was added, the upper layer was separated into a colorless and transparent aqueous layer and the lower layer was a brown organic layer in a few minutes. After separating the upper layer by decantation, 6) was added to obtain a phenol resin solution with a solid content of 54%.

[Manufacture of water-based paint]

1) 200 parts of the above purified epoxy resin (A-1) 2)
Butyl cellosolve 1103) The above carboxyl group-containing acrylic resin (B) 4) Dimethylethanolamine 135) Ion-exchanged water
5806) The above phenolic resin (C-1)
5° 1) and 2) were placed in a 4-flow flask purged with nitrogen gas and completely dissolved at 120°C, then dissolved at 100°C for 3
).

4) was added and stirred for 1 hour. Next, cool to 60℃ and
) was added dropwise over 30 minutes, and then 6) was added to reduce the solid content to 2.
A 5.1% water-based paint was obtained.

Example 2 A water-based paint was produced in the same manner as in Example 1, except that the paint was prepared without adding the phenol resin (C-1).

Example 3 [Manufacture of purified epoxy resin (A-2)] 1) Epicoat 1009 (manufactured by Yuka Shell Epoxy ■) 300 parts 2) Xylene 1003) Ethanol 400 Manufacture purified epoxy resin (A-2) using the above solvent system Thereafter, a water-based paint was produced in the same manner as in Example 1.

The characteristic values of the purified epoxy resin (A-2) are shown below together with the raw material epoxy resin (Epicoat 1009) before cleaning treatment. Note that the measurement conditions were the same as in Example 1.

Table-2 n=o n-1Mn Mn/Mw (2) (χ) Epicote 1009 1.30 1.26 3700
2.30 Purified epoxy resin 0.08 0.10
4640 1.83 Example 4 A water-based paint was produced in the same manner as in Example 3, except that the paint was prepared without adding the phenol resin (C-1>).

Example 5 (Production of epoxy acrylate resin) 1) Purified epoxy resin (A-1) 646 parts 2
) Butyl cellosolve 3493) 10%
Sodium hydroxide 14) Hydroquinone 0.025) Methacrylic acid
41) and 2) were charged into a 4-north flask purged with nitrogen gas, and stirred at 110°C for 2 hours to dissolve. Add 3) at 100°C, then heat 4)
, 5) were added.

The reaction was carried out at 130°C for 5 hours, and the mixture was taken out after cooling. The resulting resin solution had a solid content of 65% and an oxidation content of 0.2.

(Manufacture of water-based paint) 1) Methyl ethyl ketone 40 parts 2)
The above epoxy acrylate solution 1713) Styrene 16.74) Ethyl acrylate 19.55) Methacrylic acid
19.56) Butyl cellosolve
33.47) Azobisisobutyronitrile 2.48) Azobisisobutyronitrile
0.69) Methyl ethyl ketone 10
10) Dimethylethanolamine 8.011
) Ion-exchanged water 5201) was charged into a 4-tube flask purged with nitrogen gas.

While heating and refluxing, the mixed solution of 2) to 7) was added over 3 hours. After the addition was completed, the temperature was raised to 90°C, 8) was added, and after further stirring for 2 hours, the mixture was cooled to 50°C, and 9) and 10) were added. Next, 11) was added dropwise over 1 hour to obtain a water-based paint with a solid content of 20.3%.

Example 6 [Production of water-based paint] 1) Purified epoxy resin (A-1) tGo part 2
) Butylcelloselb 513) n-butanol 714) Styrene
1゜5) Ethyl acrylate
26) Methacrylic acid
3゜7) Benzoyl peroxide
38) Dimethylethanolamine 129) Ion-exchanged water 6751) and 2) were placed in a 4-flow flask purged with nitrogen gas and dissolved at 120°C, and then a mixed solution of 4) to 7) was added dropwise at 120°C over 2 hours. After further stirring at 120'C for 1 hour, the mixture was cooled to 50°C, 8) was added, and then 9) was added dropwise over 1 hour to obtain a water-based paint with a solid content of 20%.

Comparative Example 1 [Production of phenolic resin (C-2)] 1) Bisphenol A 171 parts 2) p
-Cresol 273) 37% formalin 814) 25% aqueous ammonia 125) Methyl isobutyl ketone
506) n-butanol
507) Ion exchange water 500
8) Cyclohexanone 3201) ~
4) was charged into a 4-tube flask purged with nitrogen gas and reacted for 30 minutes while heating under reflux. After completion of the reaction 5), 6
), 7) was added and allowed to stand, the lower aqueous layer was removed and 7.
8) was added to obtain a phenol resin solution with a solid content of 29.5%.

[Manufacture of epoxy/phenol paint]

1) Epicote 1009 140 parts 2)
Phenolic resin (C~2) 2033) Methyl isobutyl ketone 1004) Xylene
1005) n-butanol
1001) to 5) were replaced with nitrogen gas 4
Pour into a solo flask and react at 100℃ for 3 hours.
An epoxy-phenol paint with a solid content of 31% was obtained.

Comparative Example 2 Purified epoxy resin (8-1
) was used in the same manner as in Comparative Example 1, except that epoxy
Manufactured phenol paint.

Comparative Example 3 Epikote 100 was used instead of purified epoxy resin (A-1)
A water-based paint was produced in the same manner as in Example 2 except that No. 9 was used.

[Water flavor test]

After coating a 0.1 mm thick aluminum plate with a paint in an amount of 50 mg/100 cm, the water-based paint was baked at 200°C for 3 minutes, and the epoxy/phenol paint was baked at 200°C for 10 minutes using an electric open circuit.

After 500 cm of this coated plate was immersed in activated carbon-treated water of 10,100 O and sealed tightly, it was heat-treated at 125° C. for 30 minutes.

Changes in taste were evaluated using a sample that had been subjected to the same heat treatment without immersing the painted plate as a standard.

The evaluation criteria are as follows.

1 point...no taste 2 points...slight taste 3 points...slight taste 4 points...clear paint film taste 5 points...strong paint film taste [excessive] Potassium Manganate Consumption] The same extraction operation as in the water flavor test above was performed using distilled water, and the consumption of potassium permanganate in the extract was measured.

Table-3 Water flavor Potassium permanganate (points)
Consumption amount/ppm Example 1 1 1. 52
1 1, 83 1
1, 84 1 2, 0
5 1 1, 46 1
1, 8 Comparative example 1 5
9. 52 3 4, 2
3 3 6, 8 [Effects of the Invention] The water-based paint for the inside of cans of the present invention uses purified bisphenol-type epoxy resin in which low molecular weight substances with a molecular weight of 800 or less contained in the raw material bisphenol-type epoxy resin are reduced, and can be used as a water-based paint. This reduces the extraction of low molecular weight substances from the cured coating into the contents of the can, resulting in significant improvements in flavor and hygiene that cannot be achieved with solvent-based epoxy/phenol additives using purified epoxy resins. It brings about

Claims (1)

[Claims] 1. A resin dispersion paint in which a self-emulsifying bisphenol-type epoxy resin having a carboxyl group-containing acrylic resin moiety introduced by chemical bonding is dispersed in an aqueous medium in the presence of an amine or ammonia, As the self-emulsifying bisphenol epoxy resin, a raw material bisphenol epoxy resin having a number average molecular weight in the range of 2,000 to 6,000 and a molecular weight distribution is prepared by melting the resin in a solution of a solvable agent of the resin or by heating and melting the resin. The molecular weight contained in the resin is 800.
A water-based paint for the inside of cans, characterized by using purified bisphenol-type epoxy resin with the following components reduced or removed. 2. The self-emulsifying bisphenol-type epoxy resin is a product obtained by partially reacting a carboxyl group-containing acrylic resin and the purified bisphenol-type epoxy resin in the presence of an esterification catalyst. paint. 3. Addition polymerization of a self-emulsifying bisphenol-type epoxy resin containing an acrylic monomer to an acrylic-modified epoxy resin obtained by partially reacting the purified bisphenol-type epoxy resin with acrylic acid or methacrylic acid in the presence of an esterification catalyst. 2. The paint for the inner surface of a can according to claim 1, which is obtained by polymerizing a monomer. 4. The self-emulsifying bisphenol epoxy resin is a graft modified product obtained by polymerizing the purified bisphenol epoxy resin with an addition polymerizable monomer containing acrylic acid or methacrylic acid in the presence of a radical generator. The paint for the inside of a can as described in item 1. 5. The water-based paint for the inside of a can according to claim 1, further comprising a curing agent component of a self-emulsifying bisphenol-type epoxy resin.