JPH043905B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a heat-resistant container, and more particularly to a heat-resistant container whose contents can be heated and cooked in a microwave oven, an electric oven, or a toaster oven. (Prior Art) Tray-shaped paper containers are widely used as containers that can be easily filled with food and other contents.
In recent years, with the spread of ovens, microwave ovens, toaster ovens, etc., cooked or uncooked foods are sold in tray-shaped containers, and when eating, the containers are placed in the above-mentioned heater and heated or heated. It is desired to develop a container that can be used for shoe packing. As a response to such requests, the special public
-41890 discloses that after paper stock is prepared at near neutrality, a base paper is made by infiltrating an aqueous dispersion containing an inorganic filler, and then a heat-resistant coating is attached or laminated on both sides of the base paper. , describes a method for manufacturing paper for food containers, which comprises applying a heat-resistant resin to the surface that will become the inside of the container. In addition to aluminum foil, resins such as nitrocellulose lacquer, epoxy, urethane, and fluorine are used as the heat-resistant coating. It is also described that heat-resistant resin such as silicone-based resin is applied. (Problem to be solved by the invention) Although this container can be used for filling raw materials such as Uiro, Castella, etc. and performing heat treatment at a temperature of about 200 to 250 degrees Celsius, it can be heated in a toaster oven, etc. Alternatively, when packing is performed, the temperature of the container reaches a high temperature of 300° C. or higher, and the heat resistance is not yet fully satisfactory for such high-temperature applications. Paper cellulose fibers begin to carbonize and become colored at a temperature of about 260°C, and are completely carbonized at a temperature of about 300°C. Thus, when paper containers are used in applications where they are heated to temperatures of 300°C or higher, the appearance of the container itself becomes colored black to the extent that it cannot withstand use, and the strength of the container itself is also significantly lost. It is. In order to hide the coloring of paper containers, it is natural to consider providing a coating layer consisting of a hiding pigment and a resin binder on the surface of the paper substrate, but such coated paper generally does not have the necessary elongation to form it. There is a difficulty in press forming into chipped trays, and when the press mold is heated to improve the formability, the coating layer adheres to the mold and tends to cause defects that make molding impossible. In addition to this forming problem, conventional tray containers made of coated paper tend to emit bad odors when heated in ovens, and also have the disadvantage of impairing the flavor of foods. Therefore, the present invention provides a heat-resistant product that is composed of a paper laminate with excellent formability and has excellent appearance characteristics, container strength, and flavor retention even when the container wall is heated to a temperature of 300°C or higher. The challenge is to provide paper containers. (Means for solving the problem) The heat-resistant paper container of the present invention has a longitudinal elongation of 1.5.
% or more and a lateral elongation of 4.5% or more, and a coating layer of concealing pigment applied to both sides of the paper substrate, which is press-molded into a seamless container with a bottom. However, the coating amount of the hiding pigment is within the range of 1 to 50 g/m ² , the binder in the coat layer is composed of a thermosetting resin binder, and the binder in the coat layer has the following formula R _P = k・O _A・d _R ...(1) In the formula, O _A is the oil absorption of the hiding pigment (ml/100g), d _R represents the density of the binder (g/ml), and k is a number from 0.005 to 0.2, and it is a remarkable feature that it exists at a weight ratio (R _P ) that satisfies the following. (Function) In FIG. 1 showing a perspective view of the heat-resistant paper container of the present invention, this tray-shaped paper container has a rectangular and planar bottom wall portion 1 and a side wall portion 2 connected to the bottom wall portion 1.
a, 2b, 2c, and 2d, there are folds 3 between adjacent sidewalls, and a flange or curled portion 4 is provided on the upper edge of the sidewall. The second image shows an enlarged cross-sectional structure of the container wall of this paper container.
In the figure, this vessel wall 10 includes a paper substrate 11 and heat-resistant coating layers 12a and 12 applied to both surfaces of the paper substrate.
It consists of b. From the viewpoint of formability, it is important that the paper substrate 11 used in the present invention has an elongation of 1.5% or more in the machine direction and 4.5% or more in the transverse direction. This paper substrate 11
A coating layer of a concealing pigment is provided on the surface of the paper substrate to prevent the paper substrate from being directly exposed to a high-temperature atmosphere and to conceal carbonization of the paper substrate. Another notable feature is that the elongation of the laminate is maintained at 1.5% or more in the longitudinal direction and 4.5% or more in the lateral direction, and excellent formability is maintained. That is, according to the present invention, the coating amount of the hiding pigment is reduced to 1
^A thermosetting resin binder such as epoxy-acrylic resin is used as the binder in the coat layer ^, and the binder in the coat layer is By using the adhesive at a weight ratio (R _P ) that satisfies the above formula (1), the original formability of the paper substrate is maintained, while improving the appearance and container properties when the container is heated in an oven, etc. And flavor retention can be significantly improved. First, if the coating amount of the hiding pigment is less than the above range, the insulation effect between the paper base and the high-temperature atmosphere will be insufficient, the strength of the paper base will decrease significantly under heating, and the hiding effect of fiber carbide will be reduced. is also likely to be inadequate. Furthermore, if the amount of the pigment applied is greater than the above range, the processability will deteriorate, such as cracking, peeling, or falling off of the coating layer during molding. The above-mentioned hiding pigment is held on the surface of the paper substrate via a binder, but by using a thermosetting binder such as epoxy-acrylic resin, the moldability of the laminate can be improved. and flavor retention under heating. That is, styrene, which is conventionally used as a binder,
When butadiene copolymer latex, acrylic ester copolymer, casein, etc. are used,
There is a problem of the coating layer adhering to the press mold during molding, and there is also a problem of generation of strange odor and malodor during heating, but according to the present invention, all of the above problems are solved. In this specification, the above formula (1) has the following meaning. O _A on the right side of equation (1) is the oil absorption amount of the concealing pigment (ml/100g), and the product of this and the density d _R of the binder is calculated when the binder is the continuous phase and the pigment is the dispersed phase. pigments to the extent that they can form homogeneous compositions.
Means grams of binder per 100g. Therefore, when this composition is applied to a smooth and impermeable substrate surface such as a glass plate, k on the right side of equation (1)
When the value of k is 0.01 or more, the pigment particles are not exposed on the outer surface, and a coating layer with no voids or unevenness near the surface is formed inside, and when the value of k is less than 0.01, the pigment particles are exposed on the outer surface. Alternatively, a coating layer with irregularities may be formed inside the film, such as voids or near the surface. By the way, in the paper substrate used in the present invention, it is unavoidable that the binder permeates into the inside of the paper substrate from the surface to some extent. However, at a pigment-to-pigment binder weight ratio (R _P ) where the value of k in equation (1) is 0.2 or less, the pigment particles are exposed on the outer surface or there are voids inside the coating layer or irregularities near the surface. A laminate having such a coat layer has the same elongation as a paper substrate and can be easily formed into a tray shape. The value of k in equation (1) has a certain minimum standard value in terms of the adhesion of the hiding pigment to the paper substrate, and if the value of k is less than 0.005, the separation of the hiding pigment during molding may occur. Moreover, the heat resistance strength of the vessel wall also decreases. (Operations and Effects of the Invention) According to the present invention as described above, the paper laminate retains excellent formability while retaining its appearance characteristics, container strength, and flavor even when the container wall is heated to a temperature of 300°C or higher. It has become possible to significantly improve the retention properties, and it has been possible to provide a dual ovenable container that can be used in both a microwave oven and a toaster oven. (Description of preferred embodiments of the invention) As paper, natural pulps such as softwood pulp and hardwood pulp; inorganic fibers such as glass fiber, rock wool, slag wool, asbestos, and ceramic fiber; synthetic resins such as polyolefin, polyester, polyamide, and polyimide; Pulp 1 or 2
Examples include natural or synthetic paper obtained by paper-making more than one type of paper. These papers can be blended with fuel-retardant fillers, such as aluminum hydroxide, magnesium hydroxide, calcium aluminate, dawsonite, and the like. In addition, silica, talc, clay, calcium carbonate, etc. can be added to improve the texture and stiffness of the paper, and an organic resin binder can be added to improve paper formability and bond or fix fibers to each other. can be used. In the present invention, even when using ordinary paper obtained from wood pulp,
The advantage is that it can impart significantly better heat resistance. The basis weight of the paper substrate is 100 to 600 g/m ² , especially 150 g/m 2
It is desirable that the amount is in the range of 400 g/m ² to 400 g/m 2 . As a hiding pigment, a non-toxic or low-toxicity pigment with a high hiding power, especially a hiding power (JIS K 5101)
Pigments with a value of 40 or less are used. Examples of suitable pigments are:

【table】

[Table] These pigments may be used alone or in combination of two or more types, but the preferred pigment is one mainly composed of rutile type or anatase type titanium white (titanium dioxide). Of course, instead of using titanium white alone, for example, a small amount of yellow iron oxide, red iron oxide, or ultramarine may be blended to form a colored coating layer of cream color, pale pink, pale blue, or the like. Furthermore, fillers or extenders such as aluminum hydroxide, magnesium hydroxide, talc, clay, magnesium silicate, calcium silicate, etc. can be used in combination with this pigment. Examples of thermosetting resins include phenol-formaldehyde resin, furan-formaldehyde resin, xylene-formaldehyde resin, ketone-formaldehyde resin, urea-formaldehyde resin, melamine-formaldehyde resin, alkyd resin, unsaturated polyester resin, epoxy resin, and bismaleimide. Resins, triallyl cyanurate resins, thermosetting acrylic resins, silicone resins, etc. may be used alone or in combination of two or more. Among these, for the purpose of the present invention, it is preferable to use epoxy-acrylic resins, particularly water-soluble epoxy-acrylic resins. Suitable examples of such epoxy-acrylic resins include 12 to 30% by weight of acrylic or methacrylic acid and one of styrene, methylstyrene, vinyltoluene or a C1-C8 alkyl ester of acrylic or methacrylic acid. Or an alkali-neutralized acrylic resin (A) with a number average molecular weight of 10,000 to 100,000, which is a copolymerization of 70 to 88% by weight of two or more types, and an average of 1.1 to 2.0 per molecule.
An aromatic epoxy resin (B) having a number average molecular weight of 1,400 or more and having a number of epoxy groups is reacted with an epoxy resin with an excess of carboxyl groups and an acrylic resin partially reacted with the PH of the final coating composition. Examples include those dispersed in an aqueous medium in the presence of ammonia or amine in an amount of 5 to 11. The thermosetting resin and pigment are used in an amount ratio that satisfies the above-mentioned restrictions, and the resulting coating solution is applied onto the substrate by brush coating, spray coating, electrostatic coating, roller coating, dip coating, electrodeposition coating, etc. applied. The coated sheet is cured by heating or the action of a catalyst to form a laminate for molding. Forming into a tray is carried out by a normal press molding method using a combination of a male die (punch) and a female die (die) as appropriate depending on the type of material. From an economic point of view, it is desirable to apply a coating layer of hiding pigment to a paper substrate and then form it into a tray.
It is no problem if the paper substrate is first formed into a tray and then a coating layer of hiding pigment is applied, for example by spray painting. (Example) The present invention will be explained with the following example. Example 1 First, a water-based epoxy-acrylic paint containing titanium white as a hiding pigment was prepared by the following procedure. (A) Production of carboxyl group-containing acrylic resin Styrene 300.0 parts Ethyl acrylate 210.0 Methacrylic acid 90.0 Ethylene glycol monobutyl ether 388.0 Benzoyl peroxide 12.0 1/4 of the mixture with the above composition was replaced with nitrogen gas 4
Pour into a two-necked flask and heat to 80-90°C, keep at that temperature and gradually drop the remaining 3/4 over 2 hours. After the dropwise addition is complete, stir at that temperature for another 2 hours, then cool. Acid value 93 (solid content equivalent, same below), solid content 59.7%, viscosity 4100 cps (25℃,
A carboxyl group-containing resin solution was obtained (all viscosities below are measured at 25°C). (B) Production of epoxy resin solution Epicote 1007 500 parts Ethylene glycol monobutyl ether 333.3 Pour the entire amount into a 4-neck flask purged with nitrogen gas, gradually heat to raise the internal temperature to 100℃,
After stirring for a period of time until complete dissolution, the mixture was cooled to 80°C to obtain an epoxy resin solution with a solid content of 60%. (C) Preparation of aqueous coating resin composition 100.0 parts of the above (A) carboxyl group-containing acrylic resin solution 50.0 parts of the above (B) epoxy resin solution 2-dimethylaminoethanol 9.3 ion-exchanged water 290.7 Pour all of the above into a 4-necked flask. , was added with stirring to neutralize the contained carboxyl groups almost equimolarly, and then the internal temperature was raised to 80°C, stirring was continued at this temperature for 30 minutes, and then cooled to room temperature. . The reduction rate of oxirane % was 63.5%, and the viscosity was also 1.5 times thicker after packing compared to before packing. After kneading as described above, the solid content was 19.8 when I gradually added it little by little while stirring.
%, a slightly milky dispersion with a viscosity of 360 cps was obtained. To the thus obtained dispersion were added rutile titanium oxide with an oil absorption of 20 and a ratio of 4.2 and ion-exchanged water so that the total solid content of the resin and titanium oxide was 35%. The titanium oxide was uniformly dispersed by kneading this mixture using a ball mill type attritor. Next, stretch this titanium white-containing water-based epoxy-acrylic paint, length 2.0%, width 6.0%, basis weight 300
g/ ^m2 , softwood pulp (NBKP) 30wt%, hardwood pulp (LBKP) 70wt% as chemical pulp
%, was coated with a bar coater on both sides of a paper substrate containing 5 wt % of talc as an inorganic filler, and dried and cured in an oven at 170°C for 4 minutes. The amount of paint applied was 10 g/m ² on one side. The coating amount of the hiding pigment was 5 g/m ² . Therefore, the value of R _P is 1.0, and the range of values calculated by R _P = k・O _A・d _R is 0.12
It was within ~4.8. (However, O _A = 20, d _R = 1.2) Using the thus obtained laminate with titanium white-containing epoxy-acrylic paint coated on both sides, it was press-molded into a shape with a length of 18 cm, a width of 10 cm, and a depth of 2.
A cm square tray was molded. In this case, paint may adhere to the mold during molding, or
Molding was performed satisfactorily without any falling off. Three skewers of salted yakitori that had been stored in the refrigerator were placed in this square tray and heated in a toaster oven for 4 minutes. When the yakitori was removed from the oven after heating, it was found to be at an appropriate temperature and delicious. At this time, the surface of the square tray was not burnt and no discoloration was observed. Furthermore, the surface temperature of the square tray during heating was measured and found to be 300°C. Comparative Example 1 In Example 1, a rectangular tray made of paper without coating with titanium white-containing epoxy-acrylic paint was formed, and the same test was conducted.
After heating, the surface of the square tray had turned brown. In addition, a decrease in paper strength was observed, and the wall surface of the square tray easily broke when force was applied by hand. Comparative Example 2 In Example 2, when a titanium white-containing thermoplastic polyester paint was used instead of the titanium white-containing epoxy-acrylic paint, the paint adhered to the mold during press molding, making molding difficult. In addition, when a similar heating test using a toaster oven was conducted using an incompletely formed tray, the paint became soft due to the heat and could adhere to the contents, making it unsuitable as a container. Examples 2 and 3 and Comparative Examples 3 and 4 Using the epoxy-acrylic resin with a density of 1.2 used in Example 1 and the rutile titanium oxide with an oil absorption of 20, epoxy resin was added at the weight ratio (R _P ) shown in Table 1. - A water-based paint containing an acrylic resin was prepared, a container similar to that in Example 1 was molded, and a heating test was conducted. The results are shown in Table 1. Comparative Examples 3 and 4, in which the weight ratio of resin to pigment (R _P ) was outside the preferred range, were not suitable for toaster ovens.

【table】 [Brief explanation of drawings]

FIG. 1 is a perspective view showing the heat-resistant paper container of the present invention, and FIG. 2 is a cross-sectional structural diagram of the container wall of the paper container of the present invention. Reference numeral 1 indicates the bottom wall, 2a, 2b, 2c and 2
d is a side wall portion, 3 is a pleat portion, 4 is a flange portion or curl portion, 10 is a wall portion, 11 is a paper substrate, 12a, 1
2b indicates a heat-resistant coating layer.

Claims (1)

[Scope of Claims] 1. Consisting of a paper substrate having an elongation in the longitudinal direction of 1.5% or more and an elongation in the transverse direction of 4.5% or more, and a coating layer of a hiding pigment applied to both sides of the paper substrate, The coating amount is within the range of 1 to 50 g/m ² , the binder in the coat layer is composed of a thermosetting resin binder, and the binder in the coat layer has the following formula R _P = k・O In _{the A}・_dR formula, O _A is the oil absorption amount of the hiding pigment (ml/100g), d _R represents the density of the binder (g/ml), and k is a number from 0.005 to 0.2. A heat-resistant paper container characterized by comprising a bottomed seamless container press-molded body of a laminate existing at a satisfactory weight ratio (R _P ). 2. The heat-resistant paper container according to claim 1, wherein the thermosetting resin binder is an epoxy-acrylic resin. 3. The heat-resistant paper container according to claim 1, wherein the hiding pigment comprises titanium dioxide.