JP2003336191A - Coating agent for paper-made container and container produced by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-odor coating agent having oil resistance and water resistance and suitable for paper vessels such as paper cup and paper tray. <P>SOLUTION: The coating agent for paper vessels contains an ethylene-(meth) acrylic acid copolymer having a number-average molecular weight (Mn) of 10,000-20,000 and a (weight-average molecular weight Mw)/(number-average molecular weight Mn) ratio of 2.0-3.0. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a coating agent for a paper container and a paper container using the coating agent. More specifically, the present invention relates to a coating agent suitable for paper containers such as paper cups and paper plates. More specifically, it has good reusability as a raw material for papermaking, and is excellent in oil resistance, water resistance, and folding resistance when used as a paper cup, paper plate, etc., and is tasteless and odorless. The present invention relates to a coating agent capable of forming an excellent coating layer and a container using the coating agent.

[0002]

2. Description of the Related Art Conventionally, for oil-resistant processing of paper, there are an internal addition method in which a processing agent is added and mixed with pulp to make paper, and an external addition method in which a processing agent is impregnated or coated on raw paper. As a coating agent exhibiting excellent oil resistance in the external additive process, there is a coating agent obtained by neutralizing an ethylene- (meth) acrylic acid copolymer with ammonia. However, in the conventional ethylene- (meth) acrylic acid copolymer, the low-molecular components generated during polymerization remain and cause odors, which may cause changes in the odor and aroma of the contents and in the taste of the contents. On the other hand, there is a problem that it is not suitable as a coating agent for paper containers such as paper cups and paper plates, which are subject to severe requirements.

[0003]

An object of the present invention is to provide a coating agent having oil resistance and water resistance and having a low odor suitable for paper containers such as paper cups and paper plates.

[0004]

Means for Solving the Problems As a result of intensive investigations by the present inventors, it was found that an ethylene- (meth) acrylic acid copolymer having a small amount of low-molecular components can form a tasteless and odorless coating layer or impregnated layer. And completed the present invention. That is, the first invention is the number average molecular weight (Mn) = 10000.
To 20000, weight average molecular weight (Mw) / number average molecular weight (Mn) = 2.0 to 3.0 ethylene- (meth) acrylic acid copolymer (B), for a paper container It is a coating agent.

In a second aspect of the invention, the ethylene- (meth) acrylic acid copolymer (B) has a number average molecular weight (Mn) of 700.
No. 0 to 10,000, weight-average molecular weight (Mw) / number-average molecular weight (Mn) = 3.2 to 4.2 Ethylene- (meth) acrylic acid copolymer (A), characterized by being purified A coating agent for paper containers according to the first aspect of the invention.

The third invention is the first or second invention characterized in that the ethylene- (meth) acrylic acid copolymer (B) is dispersed in an aqueous medium in the presence of a basic compound. The coating agent for paper containers described in 1.

A fourth invention is a paper container characterized in that a paper base material is coated with the coating agent according to any one of the first to third inventions.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION First, the coating agent for paper containers of the present invention will be described. The coating agent for a paper container of the present invention has Mn = 10000 to 20000, Mw / M.
It contains an ethylene- (meth) acrylic acid copolymer (B) with n = 2.0 to 3.0. In other words, the ethylene- (meth) acrylic acid copolymer (B) has a small amount of low molecular weight components and a sharp molecular weight distribution. By using such a low amount of low molecular weight components,
It is possible to form a tasteless and odorless coating layer.

The ethylene- (meth) acrylic acid copolymer (B) can be obtained by various methods. For example, Mn = 7000 to 10000, Mw / Mn = 3.
The ethylene- (meth) acrylic acid copolymer (A) containing a large amount of relatively low molecular components having a molecular weight distribution of about 2 to 4.2 is purified to remove the low molecular components, or the synthesis conditions (catalyst, By controlling the temperature, the reaction ratio, etc.), a low molecular weight component and a sharp molecular weight distribution may be obtained.

The former, that is, Mn = 7000 to 1000
The ethylene- (meth) acrylic acid copolymer (A) having a relatively low molecular weight component and a molecular weight distribution of 0, Mw / Mn = 3.2 to 4.2 is purified to remove the low molecular weight component. The method will be described. Among the ethylene- (meth) acrylic acid copolymers (A), the ethylene-acrylic acid copolymers include “PRIMACOR 5990 manufactured by Dow Chemical Co., Ltd.
I ”(Mn = 9100, Mw / Mn = 3.4) and the like.

As a method for removing the low-molecular component, a method of washing the copolymer (A) or a method of sealing the copolymer (A) in a closed container is used.
And a method of distilling off low-molecular components, separation by a column, recrystallization and the like.

A method for washing the copolymer (A) will be described. Examples of the method for washing the copolymer (A) include (a) reprecipitation method, (b) Soxhlet extraction method, (c) alcohol stirring method and the like.

(A) Reprecipitation method: The copolymer (A) is dissolved in a mixed solvent such as methyl ethyl ketone / toluene under heating and then cooled, and the copolymer (B) is reprecipitated and removed at a low temperature. Separate the solution of the molecular component and the copolymer (B).

(B) Soxhlet extraction method: A copolymer (A) is put into a filter for Soxhlet extraction, a solvent which does not dissolve the copolymer (B) but can dissolve a low molecular component at least under heating, Soxhlet extract low molecular components.
Examples of the solvent capable of dissolving the low molecular weight component at least under heating include alcohols such as methanol.

(C) Alcohol stirring method: A method which can be said to be a modification of the Soxhlet extraction method, in which the copolymer (B) is not dissolved and the low-molecular component is at least dissolved in a solvent which can be dissolved under heating. ) Is added and the low molecular component in the copolymer (A) is dissolved under stirring to separate the solution of the low molecular component to be removed from the copolymer (B).

From the viewpoint of Mw, the copolymer (A) and the copolymer (B) from which the low molecular weight components have been removed are not so different from each other. However, the effect of removing low-molecular components is that Mn and M
Remarkably appeared in w / Mn, Mn = 7000-10000,
What was Mw / Mn = 3.2-4.2 was Mn = 1.
It becomes 20,000 to 20,000 and Mw / Mn = 2.0 to 3.0. In other words, Mn = 10000 to 20000, M
It is important to use the copolymer (B) purified until w / Mn = 2.0 to 3.0 in a coating agent for a paper container, and Mn = 11000 to 18000, Mw / M.
It is preferable to use the copolymer (B) having n = 2.0 to 2.8. When the Mn value of the copolymer (B) is less than 10000 or the Mw / Mn value is more than 3.0, a large amount of low-molecular components that cause odor is contained. Is unsuitable as a coating agent for paper containers.

The low-molecular component removed is Mn = 1500.
˜3000, Mw = 2500-8500, and a large amount of oxide is contained. That is, as compared with the copolymer (A) and the copolymer (B), the low-molecular component to be removed contains a large amount of carbonyl groups. IR (infrared absorption spectrum) of the copolymer (A), the copolymer (B), and the low-molecular component to be removed was measured by IR (infrared absorption spectrum), and the absorption spectrum intensity of ethylene part (absorption at 2850 to 2855 cm ^-1 ) Absorption spectrum intensity of the carbonyl group for (17
The absorption ratio at 05 cm ⁻¹ is calculated. When a copolymer (A) having a carbonyl group strength S of about 0.87 is purified to obtain a copolymer (B) having a carbonyl group strength S of about 0.86, a low-molecular-weight carbonyl group to be removed The strength S is about 2.6 for the reprecipitation method and about 1.3 for the Soxhlet extraction method. Further, the acid value of the copolymer (B) after purification is slightly smaller than that of the copolymer (A). For example, acid value 16
When the copolymer (A) of about 5 (mgKOH / g) is purified, it has an acid value of about 155 (mgKOH / g) in the case of the reprecipitation method and an acid value of about 160 (mgKOH / g) in the case of the Soxhlet extraction method. A copolymer (B) is obtained.

The ethylene- (meth) acrylic acid copolymer referred to in the present invention is an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-acrylic acid-methacrylic acid copolymer, And the compositions in which they are in a mixed state. Further, Mn and Mw / Mn in the present invention are values obtained by gel permeation chromatography in terms of styrene.

By using the ethylene- (meth) acrylic acid copolymer (B) from which the low-molecular component is thus removed, a tasteless and odorless coating layer or impregnation layer can be formed on the paper substrate. . Examples of the coating agent of the present invention include those in which the ethylene- (meth) acrylic acid copolymer (B) is dispersed in an aqueous medium, dissolved in an organic solvent, or heated and melted.
Those dispersed in an aqueous medium are preferred.

As the aqueous dispersion of the ethylene- (meth) acrylic acid copolymer (B), for example, the ethylene- (meth) acrylic acid copolymer (B) is dispersed in an aqueous medium in the presence of a basic compound. Can be obtained. Specifically, it is preferable to neutralize the ethylene- (meth) acrylic acid copolymer (B) with a basic compound and water in a state of being heated to 90 ° C to 110 ° C. Examples of the basic compound include ammonia, alkali metal salts, alkaline earth metal salts, organic amine compounds and the like, and these can be appropriately used in combination. Ammonia water and an alkali metal salt are used in combination to make ethylene- (meth) acrylic acid copolymer (B) aqueous, or ethylene- (meth) acrylic acid copolymer (() made aqueous in the presence of aqueous ammonia ( B) and ethylene- (meth) hydrated in the presence of an alkali metal salt
Mixing with the acrylic acid copolymer (B) is preferable because not only oil resistance but also water vapor barrier property can be improved.

Examples of alkali metal salts include alkali metal hydroxides and alkali metal carbonates, and examples of alkali metal hydroxides include lithium hydroxide, potassium hydroxide, sodium hydroxide, and the like. Examples of the alkali metal carbonate include lithium carbonate, potassium carbonate, sodium carbonate and the like. Examples of the alkaline earth metal salt include magnesium hydroxide, calcium hydroxide, magnesium carbonate, calcium carbonate and the like. Examples of the organic amine compound include alkylamines such as trimethylamine and triethylamine, and alcohol amines such as dimethylaminoethanol and diethanolamine. Examples of the aqueous medium include water, and a hydrophilic organic solvent can be used together.

The coating agent of the present invention may contain a filler, a thixotropy imparting agent, a coloring pigment, an extender pigment, a dye, an antioxidant, an antioxidant, an antistatic agent, if necessary, within a range that does not impair the effects of the present invention. , Flame retardants, thermal conductivity improvers, plasticizers, anti-sagging agents, antifouling agents, antiseptics, bactericides, defoamers, leveling agents, UV absorbers, and various other additives may be added. .

Next, the paper container of the present invention will be described.
The paper container of the present invention is formed by applying a coating agent containing the copolymer (B) onto a paper base material and impregnating the paper base material with the coating agent to form an impregnated layer, or forming from the coating agent. A processed paper obtained by forming a coating layer on a paper substrate is formed into a container shape such as a cup or a plate by a conventional method. For example, punch a processed paper to a specified size with a punching device, and if necessary, set a specified ruled line, bend it or roll it into a cylinder, and heat the part to be overlapped and bonded to co-load. By melting the united product (B), a paper container can be made.

To apply an aqueous dispersion of the copolymer (B) or an organic solvent solution to a paper substrate, for example, when forming an impregnation layer, various impregnation machines such as size press, calender, size, and When forming the coating layer, a coater such as a spray, a roll coater, a knife coater, or a gravure coater can be used. The applied amount varies depending on the paper quality and the required oil resistance, but it is 3 to 7 in dry.
It is preferable to apply about g / m ² .

[0025]

EXAMPLES Next, examples of the present invention will be specifically described. Example 1 An ethylene-acrylic acid copolymer manufactured by Dow Chemical Co., Ltd. in pellet form, PRIMACOR, was put into a flask having an internal volume of 1000 ml equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introducing tube.
5990I (Mn = 9100, Mw = 31000, Mw /
Mn = 3.4, acid value = 165 (mgKOH / g)) 50 g,
375 g of methyl ethyl ketone and 125 g of toluene were charged, and the mixture was heated and dissolved while stirring under a nitrogen stream. When completely dissolved, the heating was stopped and the mixture was gradually cooled at room temperature to form a precipitate, the precipitate was separated by suction filtration, and the solvent was removed by a vacuum dryer. The ethylene-acrylic acid copolymer obtained by the reprecipitation treatment has Mn = 17,000, Mw = 36000,
The Mw / Mn was 2.1 and the acid value was 155 (mgKOH / g). )

In a flask having an inner volume of 300 ml equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introducing tube, 20 g of the ethylene-acrylic acid copolymer obtained by the above reprecipitation treatment, 2
7 g of 8% ammonia water and 73 g of water were charged, and the temperature was raised to 95 ° C. with stirring under a nitrogen stream. The mixture was stirred for about 3 hours to obtain an aqueous dispersion of a translucent aqueous solution or an emulsion of neutralized ammonia having a solid content of 20%.

Example 2 An ethylene-acrylic acid copolymer manufactured by Dow Chemical Co., Ltd., PRIMACOR 5990I (Mn = 9100, Mw = 310) was used as a pellet in a filter in the Soxhlet extractor.
00, Mw / Mn = 3.4, acid value = 165 (mgKOH /
(g)) (19.94 g) and methanol (150 g) as an extraction solvent were charged into the flask, and extraction was performed for about 5 hours. When the pellet-shaped substance remaining in the filter was taken out and methanol was removed by a vacuum dryer, the weight was 19.82.
It was g, and the weight loss was 0.6%. Mn = 12000, Mw = 3 of the obtained ethylene-acrylic acid copolymer
2000, Mw / Mn = 2.8, acid value = 160 (mgKOH
/ G). Further, the solvent of the extract was removed by an evaporator, and the remaining components were Mn = 1600 and Mw = 35.
00, the acid value was 228 (mgKOH / g).

A flask having an internal volume of 300 ml equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introducing tube was charged with 20 g of the pellets obtained by the Soxhlet extraction treatment, 7 g of 28% ammonia water, and 73 g of water, and a nitrogen stream was introduced. The temperature is raised to 95 ° C. with stirring underneath. The mixture was stirred for about 3 hours to obtain an aqueous dispersion of a translucent aqueous solution or an emulsion of neutralized ammonia having a solid content of 20%.

Example 3 In a flask having an internal volume of 300 ml equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introducing tube, pelletized ethylene-acrylic acid copolymer manufactured by Dow Chemical Co., Ltd., PRIMACOR
5990I (Mn = 9100, Mw = 31000, Mw /
Mn = 3.4, acid value = 165 (mgKOH / g)) 30 g,
100 g of methanol was charged, and the temperature was raised to 50 ° C. under a nitrogen stream while gently stirring so as not to break the pellets. After stirring for about 2 hours, heating and stirring were stopped and the supernatant methanol was removed. 100 g of methanol was poured again, the mixture was stirred at 50 ° C. for about 2 hours, and then the supernatant methanol was removed. This was repeated again, and stirring was carried out 3 times in total.
After removing the methanol, the pellet was dried in a vacuum dryer. Mn of the obtained ethylene-acrylic acid copolymer
= 12000, Mw = 32000, Mw / Mn = 2.
7. Acid value = 160 (mgKOH / g).

A flask having an internal volume of 300 ml equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introducing tube was charged with 20 g of the pellet obtained by the above methanol stirring treatment, 7 g of 28% ammonia water, and 73 g of water, and a nitrogen stream was introduced. The temperature is raised to 95 ° C. with stirring underneath. Stir for about 3 hours to obtain a solid content of 2
An aqueous dispersion was obtained in a 0% translucent aqueous solution or an ammonia neutralized product of an emulsion.

Comparative Example 1 In a flask having an inner volume of 300 ml equipped with a cooling tube, a stirrer, a thermometer, and a nitrogen introducing tube, pelletized ethylene-acrylic acid copolymer manufactured by Dow Chemical Co., Ltd., PRIMACOR
5990I (Mn = 9100, Mw = 31000, Mw /
Mn = 3.4, acid value = 165 (mgKOH / g)) 20 g,
7% of 28% ammonia water and 73 g of water were charged, and the temperature was raised to 95 ° C while stirring under a nitrogen stream. The mixture was stirred for about 3 hours to obtain an aqueous dispersion of a translucent aqueous solution or an emulsion of neutralized ammonia having a solid content of 20%.

Examples 1 to 3 produced as described above,
Using the aqueous dispersion obtained in Comparative Example 1, test pieces 1, 2
Was prepared, and a sensory test for changes in odor (test piece 1) and taste (test piece 2), and oil resistance (test piece 1) and water resistance (test piece 1) tests were conducted as follows.

Specimen 1: The aqueous dispersions obtained in Examples 1 to 3 and Comparative Example 1 were coated on one side of a paper cup paper with a bar coater No. No. 16 was used for coating and dried in an oven at 140 ° C. for 1 minute. Specimen 2: The aqueous dispersions obtained in Examples 1 to 3 and Comparative Example 1 were coated with a bar coater No. 16 was used, and after predrying in an oven at 80 ° C. for 30 seconds, the back surface was similarly coated and predried. Then, it was dried at 140 ° C. for 1 minute.

(1) Flavor (Odor) Test Specimen 1 was cut into 15 cm ² , put in a glass bottle, and 100 g of boiling water was poured from above, and the odor intensity was evaluated by 10 panelists. The judgment was scored according to the following three-step criteria, and the average score was shown. [Scoring criteria] 1: No odor. 2: Slightly odorous. 3: It smells clearly.

(2) Taste test The test piece 2 was cut into 500 cm ² , put in a pressure bottle and poured with 500 g of purified water, boiled for 30 minutes, cooled to room temperature with cold water, and used as a sample for taste evaluation. Also,
Only purified water was put in a pressure bottle and boiled for 30 minutes, and then cooled to room temperature to give a blank. The purified water in this bottle was put in a glass cup and the taste was evaluated by the panelists. In addition, the judgment was scored on the basis of the following 5 grades as compared with the blank, and the average score was shown. [Scoring Criteria] 1: No offensive odor or change in taste. 2: There is a slight offensive odor or a change in taste. 3: There is a distinct offensive odor or change in taste. 4: There is considerable off-flavor or change in taste. 5: There is a strong difference in odor or taste.

(3) Oil resistance test (according to TAPPIUM-557) A few drops of the mixed oil shown in Table 2 were dropped on the coating layer surface of the test piece 1, and 15 seconds later, black spots appeared on the surface coated by the penetration of oil drops. When it occurred, it was rejected, and the maximum oil resistance of oil droplets that did not penetrate was taken as the oil resistance of the test piece.

(4) Water resistance test Several drops of water were dropped on the surface of the coating layer of the test piece 1, and 1 hour later, the state of permeation of water drops was visually evaluated.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

As described above, by using an ethylene-acrylic acid copolymer having a low molecular weight component and a sharp molecular weight distribution, it has oil resistance and water resistance, has a low odor and spoils the taste of the contents. Of course, it is possible to obtain a coating agent suitable for a paper container such as a paper cup or a paper plate. Further, by using a paper coated with a coating agent containing such an ethylene- (meth) acrylic acid copolymer, an excellent tasteless and odorless paper container can be obtained.

Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) B65D 5/62 B65D 65/42 C 65/42 C09D 5/00 Z C09D 5/00 123/08 123/08 133/02 133/02 B65D 5/42 ZF Term (Reference) 3E060 BC04 BC08 DA30 3E086 AB02 AD05 AD06 BA04 BA14 BA24 BB71 BB74 BB90 CA01 CA11 DA01 4J038 CB061 HA116 HA306 JB01 MA08 MA10 MA14 NA04 NA07 NA27 PB04 PC10 4L055 AG59 AG71 AG71 AJ02 BE08 BE09 EA30 FA19 GA05

Claims (4)

[Claims] 1. A number average molecular weight (Mn) = 10000 to 2
0000, weight average molecular weight (Mw) / number average molecular weight (M
n) = 2.0-3.0 ethylene- (meth) acrylic acid copolymer (B) is contained, The coating agent for paper containers characterized by the above-mentioned. 2. The ethylene- (meth) acrylic acid copolymer (B) has a number average molecular weight (Mn) of 7,000 to 1,000.
0, weight average molecular weight (Mw) / number average molecular weight (Mn) =
The ethylene- (meth) acrylic acid copolymer (A) of 3.2 to 4.2 is purified, and the coating agent for a paper container according to claim 1. 3. The paper container according to claim 1 or 2, wherein the ethylene- (meth) acrylic acid copolymer (B) is dispersed in an aqueous medium in the presence of a basic compound. Coating agent. 4. A paper container comprising a paper base material coated with the coating agent according to any one of claims 1 to 3.