JPH0436935B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a heat-resistant container, and more particularly, to a method for manufacturing a heat-resistant paper container whose contents can be heated and cooked in a microwave oven, microwave oven, or 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. (Problems to be Solved by the Invention) Although the above-mentioned 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 cannot be used in a toaster oven or the like. When heating or shoeing,
The temperature of the container reached a high temperature of 300°C or higher, and the heat resistance was 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 has a high elongation required for molding. 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 it impossible to form, and it also does not adhere to the mold. Even if the mold is molded, the resin gradually adheres and accumulates on the surface of the mold, which tends to reduce molding workability and cause poor appearance of the molded container. Although this tendency may be slightly reduced by applying a mold release agent to the surface of the mold, it is not a fundamental solution to the above problem. Therefore, the present invention provides good appearance characteristics, even when the container wall is heated to a temperature of 300°C or higher in a toaster oven, various ovens, microwave ovens, etc.
The object of the present invention is to provide a method for producing heat-resistant paper containers having container strength and flavor retention without the aforementioned tendency to stick to molds and with excellent molding workability. (Means for Solving the Problems) According to the present invention, a laminated material consisting of a paper substrate and a paint film applied to both sides of the paper substrate is press-molded into a tray shape using a heated mold. In the manufacturing method of heat-resistant paper containers, the glass transition point after curing measured with a scanning calorimeter is 90°C or higher and 130°C.
A hiding pigment is blended into the following thermosetting paint, and the weight ratio of thermosetting resin per hiding pigment (R _P ) is
is the following formula R _P = k・O _A・d _R In the formula, O _A is the oil absorption amount of the hiding pigment (ml/100g), d _R is the density of the resin (g/ml), and k is
Prepare a coating solution that satisfies , which is a number between 0.005 and 0.2; Apply this coating solution to both sides of the paper substrate; Cure the coating formed to give a vertical 1.5% or more elongation in the direction, 4.5 in the lateral direction
% or more; and supplying the laminated material to a mold heated to 50°C to 180°C to perform press molding. be done. (Function) A first perspective view showing a heat-resistant paper container according to the present invention.
In the figure, this tray-shaped paper container consists of a rectangular and planar bottom wall 1 and side walls 2a, 2b, 2c, and 2d that are connected to the bottom wall 1. There is a pleated portion 3, and a flange portion or curled portion 4 is provided at the upper end edge of the side wall portion. In FIG. 2, which shows an enlarged cross-sectional structure of the laminated material used for manufacturing this paper container, this laminated material 10
consists of a paper substrate 11 and heat-resistant coating layers 12a and 12b applied to both surfaces of the paper substrate. In the present invention, the heat-resistant coating layers 12a, 12
The first feature of b is that a thermosetting paint containing a hiding pigment is used. First, this coating 12a,
When a thermoplastic resin is used as 12b, it tends to cause molding problems such as the coating sticking tightly to the mold when press-molding into a container, and it also generates bad odor, strange taste, and odor when heated in an oven etc. In addition to impairing the flavor of foods,
Although there is a remarkable tendency for the container strength itself to decrease, by using a thermosetting resin as the coating component, the above-mentioned disadvantages can be eliminated or alleviated. Furthermore, the hiding pigment contained in this paint has the effect of thermally insulating the paper substrate 11 from the heated high-temperature atmosphere, thereby maintaining the tendency of the paper substrate to decrease in strength under heating to a small level. At the same time, the coating itself also has the effect of imparting heat resistance and concealing fiber carbide generated on the paper substrate to maintain a good appearance.
Furthermore, the hiding pigments contained in the paint also serve an auxiliary function, somewhat reducing the formation and accumulation of resin stickies on the mold surface. The present invention further provides a thermosetting paint coating with a glass transition temperature (Tg) as measured by a scanning calorimeter (DSC).
The second feature is that by using a material whose temperature is in the range of 90 to 130°C, the moldability is improved while preventing the formation and accumulation of sticky substances on the mold surface. Glass transition, as is well known, is a phenomenon in which a polymer substance changes from a glassy, hard state to a rubbery state, and the temperature at which this occurs is Tg.
However, when measured using a scanning calorimeter, it appears as a shoulder-like endotherm, which is the point at which the motion of the frozen molecular chains begins. This Tg generally increases as the degree of crosslinking increases for thermosetting resins. It can be said that the thermosetting resin used in the present invention having a Tg in the range of 90 to 130°C has a degree of crosslinking that is approximately in the middle. When Tg is lower than 90℃, it is difficult to eliminate adhesive formation and accumulation on the heated mold surface, even with a thermosetting resin coating; on the other hand, when Tg is lower than 130℃ If the amount is also high, the processability of the coating will be poor, resulting in poor formability of the laminate. In the present invention, by using a thermosetting resin having a Tg of 90° C. or higher, the tendency of adhesive substances to adhere to the mold surface is suppressed, presumably for the following reasons. In other words, it is thought that thermosetting resins contain relatively low molecular weight components and uncondensed components, but by using a resin with a Tg of 90°C or higher, molecular chain movement is suppressed up to relatively high temperatures. It is thought that this is because the movement of the component is suppressed by crosslinking between molecular chains, thereby suppressing its transfer to the mold surface. The weight ratio (R _P ) of the thermosetting resin per hiding pigment in the thermosetting paint coating layer is determined by the following formula: R _P =k・O _A・d _R ……(1) In the formula, O _A is the weight ratio of the hiding pigment. is the adsorption amount (ml/100g), d _R represents the density of the resin (g/ml), and k is
It is also important that the number is within the range of 0.005 to 0.2. 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 hiding pigment (ml/100g), and the product of this and the density of the resin indicates that a homogeneous composition in which the resin is a continuous phase and the pigment is a dispersed layer is formed. 100g of pigment, within the limits possible
It means the minimum number of grams of binder per unit (in relation to R _P , k corresponds to 1/100, ie 0.01). Therefore, when this composition is applied to a smooth and impermeable substrate surface such as a glass plate, formula (1) is obtained.
When the value of k on the right side of
If it is less than 0.01, pigment particles are exposed on the outer surface,
Alternatively, a coat phase with unevenness is formed inside the film, as well as in voids and near the surface. By the way, in the present invention, the lower limit of the value of k in formula (1) is specified as 0.005 because the substrate on which the coating layer is provided is paper, has unevenness, and has an anchoring effect on the hiding pigment. This is because the use of a resin amount slightly lower than the minimum resin amount (k = 0.01) is allowed. However, if the value of k is less than 0.005, the hiding pigment may come off during molding, and the heat resistance strength of the vessel wall will also decrease. Also, the upper limit of the value of k is specified as 0.2 because
The resin tends to penetrate somewhat into the paper substrate;
Weight ratio of pigment to resin (R _P ) where the value of k is 0.2 or less
In this case, pigment particles are exposed on the outer surface or a coating layer with unevenness is formed near the surface, and a laminate with such a coating layer has the same elongation as a paper substrate and cannot be formed into a tray shape. Although easily carried out, for pigment-to-resin weight ratios where the value of k exceeds 0.2,
This is because the pigment particles become embedded in the resin and the anti-adhesive effect is lost, and the hiding effect and heat shielding effect are also reduced. According to the present invention, molding workability is improved by setting the weight ratio of resin per hiding pigment within a certain range based on the oil absorption amount of the pigment and the density of the resin.
It prevents mold sticking and provides excellent hiding and heat shielding effects. The laminated material 10 used in the present invention is 20°C, 65%
It has an elongation of 1.5% or more in the longitudinal direction and an elongation of 4.5% or more in the lateral direction, as measured by RH, which makes it possible to form a seamless container with a bottom by press molding. (Operations and Effects of the Invention) According to the present invention, even when press molding is performed using a heated mold using a laminate in which a resin coating layer is provided on both sides of a paper substrate, adhesive substances may not be deposited on the surface of the mold. This prevents the adhesion and accumulation of particles, resulting in good molding workability, allowing the paper laminate to maintain excellent moldability, and maintaining the appearance characteristics of the container even when the container wall is heated to a temperature of 300°C or higher. , it became possible to significantly improve the container strength and flavor retention characteristics, and it was possible to provide a dual ovenable container that can be used in both a microwave oven and a toaster oven. (Description of structure of the invention) Thermosetting resin In the present invention, the Tg measured by the above measurement method is 90
Within the range that satisfies the conditions of 130℃ to 130℃,
Any thermosetting resin, such as phenol-formaldehyde resin, furan-formaldehyde resin, xylene-formaldehyde resin, ketone-formaldehyde resin
Formaldehyde resin, urea-formaldehyde resin, melamine-formaldehyde resin, alkyd resin, unsaturated polyester resin, epoxy resin, bismalemide resin, triallyl cyanurate resin, thermosetting acrylic resin, silicone resin, etc. alone or in combination of two or more combination is used. Among these, in the present invention, a combination of an epoxy resin and a reactive acrylic resin and/or vinyl resin having a functional group such as a carboxyl group, a hydroxyl group, or an amino group, such as a group reactive with the epoxy resin, is used. be. These epoxy/acrylic or epoxy/vinyl coatings are particularly suitable for the purposes of the present invention in that they have excellent processability under crosslinked conditions and less stickiness formation on mold surfaces. . As an epoxy resin component, bisphenol A
Aromatic epoxy resins obtained by condensing epoxy and epihalohydrin are particularly suitable, and their epoxy equivalents are generally in the range of 1,000 to 4,000. As the acrylic resin, the monomer components providing the functional groups include unsaturated carboxylic acids such as methacrylic acid, acrylic acid, and maleic anhydride, or their anhydrides; (meth)acrylic acid-2-hydroxyethyl ester; (meth)acrylic acid-2
-Hydroxy group-containing monomer; (meth)acrylic acid-2-aminoethyl ester, (meth)acrylic acid-2-N,N-diethylaminoethyl ester, (meth)acrylic acid-N-aminoethyl-a

【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 coat 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. Paper substrate Paper can be one of natural pulps such as softwood pulp and hardwood pulp, inorganic fibers such as glass fiber, rock wool, slag wool, asbestos, and ceramic fibers; synthetic resin pulps such as polyolefin, polyester, polyamide, and polyimide; Examples include natural or synthetic paper obtained by paper-making two or more types. 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 . Manufacture of laminated material The laminated material used in the present invention is prepared by preparing a coating liquid containing the above-mentioned thermosetting resin and hiding pigment, applying this coating liquid to both sides of a paper substrate, and curing the formed coating. It can be obtained by To explain how to calculate the pigment-to-resin weight ratio (R _P ) in formula (1) above, if the oil absorption amount of the hiding pigment is 20
ml/100g and the density of the thermosetting resin is 1.2g/ml, the value of O _A · d _R is calculated as 24. When k is 0.005, R _P is 0.12, and when k is 0.2, R _P is 4.8, which is 17.2 when converted to the pigment concentration per entire coating.
It corresponds to ~89% by weight. The solid content concentration of the coating solution is such that the amount of solvent is as low as possible within a range that provides uniform coating properties, and is generally in the range of 20 to 80% by weight. Coating means such as spray coating, electrostatic coating, roller coating, dipping coating, and electrodeposition coating are used for coating. The amount applied to the paper substrate is 2 to 30% as solid content.
g/m ² , especially 5 to 20 g/m ² ,
A satisfactory combination of heat resistance and processability is obtained. Curing of the coating formed takes place by means known per se, such as catalysis, heating or irradiation with ultraviolet light or radiation. Forming into a container Forming into a bottomed seamless container such as a tray, bowl, or cup is performed by heating a male mold and a female mold, supplying a laminated material between them, and press-forming. By heating the mold, the molding of the laminated material is dramatically improved compared to the case where an unheated mold is used. The heating temperature of the mold is generally 50 to 50℃.
The temperature is preferably 180°C, particularly in the range of 90 to 150°C. The invention is illustrated by the following example. (Examples) 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 acrylic resin containing carboxyl group 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 placed in a 4-neck flask purged with nitrogen gas 80 Heat to ~90℃ and gradually drop the remaining 3/4 over 2 hours while keeping at that temperature.
After stirring for an hour, it was cooled and the acid value was 93 (solid content equivalent).
(same below), solids content 59.7%, viscosity 4100cps (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 50 parts ethylene glycol monobutyl ether
333.3 Pour the entire amount into a 4-necked flask purged with nitrogen gas, gradually heat to raise the internal temperature to 100℃, and
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-dimethylaminomethanol 9.3 Ion exchange water 290.7 Total amount in a 4-necked flask After the mixture was charged and added with stirring to neutralize the contained carboxyl groups almost equimolarly, the internal temperature was raised to 80°C, stirring was continued at this temperature for 30 minutes, and then the mixture was cooled to room temperature. The reduction rate of oxirane% is
The viscosity was 63.5%, and the viscosity was 1.5 times higher after shoeing than before shoeing. 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, rutile titanium oxide with an oil absorption of 20 and a specific gravity of 4.2 and ion-exchanged water were added in an amount equal to the solid content, and the total solid content of the resin and titanium oxide was adjusted to 35%. This mixture was kneaded using a ball mill type attritor to uniformly disperse titanium oxide. The resin density d _R (g/ml) of this titanium oxide dispersed epoxy acrylic paint is 1.20, the oil absorption amount O _A (ml/100 g) of the hiding pigment is 20, k is 0.042, and the weight ratio of the epoxy acrylic resin is present. R _P is 1.0. The titanium white-containing water-based epoxy-acrylic paint thus obtained was applied onto a glass plate.
After curing in the oven for 1 minute at 190℃,
The paint film was peeled off. The glass transition temperature (Tg) of this paint film was measured using a scanning calorimeter (DSC) and was found to be 115°C. Next, apply this titanium white-containing epoxy-acrylic paint with elongation of 2.0% vertically, 6.0% horizontally, and basis weight.
300g/ ^m2 , softwood pulp (NBKP) 30% by weight, hardwood pulp (LBKP) 70% as chemical pulp
% by weight, applied with a bar coater to both sides of a paper substrate containing 5% by weight of talc as an inorganic filler,
Dry cured in an oven at 190°C for 1 minute.
The amount of paint applied was 14 g/m ² on one side. The coating amount of the hiding pigment was 7 g/m ² . The elongation at break of the thus obtained laminate coated with titanium white-containing epoxy-acrylic paint on both sides was measured using a tensile tester at a tensile speed of 4 mm/min.
When measured, it was 2.6% in the vertical direction and 5.8% in the horizontal direction. Next, using a laminate coated with this titanium white-containing epoxy-acrylic paint on both sides, blanking and creasing are performed, and then press molding is performed using a press mold held at 140°C. A square tray with a length of 16 cm, a width of 9.5 cm and a depth of 2 cm as shown in FIG. 1 was obtained. In this case, during molding, the paint did not adhere to or fall off the mold, and molding was performed satisfactorily without any cracks or breaks. Put 3 skewers of yakitori with barrels into this square tray,
After storing it in the refrigerator for 2 days, it was 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. Examples 2 to 5, Comparative Examples 1 to 6 The coatings shown in Table 1 were applied to both sides of the paper substrate used in Example 1 using a bar coater so that the coating amount was 14 g/m ² of solids per side. Dry cured in an oven at 190°C for 4 minutes. The Tg and elongation at break of the laminate measured by DSC after curing were as shown in Table 1. In addition, the d _R of the paint used in each example and comparative example,
The values of O _A and R _P are shown in Table 2. Next, each laminate was blanked and ruled, and then a press mold kept at 140°C was used to form a shape of 16 cm long and 9.5 cm wide as shown in Figure 1.
It was molded into a square tray with a depth of 2.0 cm. Table 1 shows the press formability in this case, that is, the degree of paint adhesion to the mold, paint falling off, paint cracking, and laminate breakage. As is clear from the table, when the elongation at break of the laminate was low, there was a tendency for the laminate to break or crack during molding. Also
When a low Tg paint was used, the paint adhered to the mold during molding. Comparative Example 7 Both sides of the paper substrate used in Example 1 had a density of 1.20,
Oil absorption in epoxy-acrylic resin with Tg of 98℃
A coating material containing 90% by weight of titanium white No. 20 was applied using a bar coater to give a solid content of 14 g/m ² per side, and dried and cured in an oven at 190° C. for 4 minutes. Next, using this laminate, after blanking and scoring, a press mold kept at 140°C was used to form a rectangular tray measuring 16 cm long, 3.5 cm wide, and 2.0 cm deep, as shown in Figure 1. was molded. Since the k value of the paint used in this case was lower than 0.005,
Paint came off during molding, and cracks in the paint and rupture of the laminate were also observed.

【table】

【table】

【table】

【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. A method for producing a heat-resistant paper container, which comprises press-molding a laminated material consisting of a paper substrate and a paint film applied to both sides of the paper substrate into a tray shape using a heated mold, A hiding pigment is blended into a thermosetting paint whose glass transition point after curing is 90°C or higher and 130°C or lower as measured by a scanning calorimeter, and the weight ratio of thermosetting resin per hiding pigment (R _P ) is calculated. is the following formula R _P = k・O _A・d _R In the formula, O _A is the oil absorption amount of the hiding pigment (ml/100g), d _R is the density of the resin (g/ml), and k is
Prepare a coating solution that satisfies the following, which is a number between 0.005 and 0.2; Apply this coating solution to both sides of the paper substrate; Cure the coating formed at 20°C and 65% RH.
elongation of 1.5% or more in the longitudinal direction, measured in the transverse direction
Manufacture a laminated material with an elongation of 4.5% or more; 50
A method for manufacturing a heat-resistant paper container, which comprises supplying the laminated material to a mold heated to 180°C to 180°C to perform press molding. 2. The method for producing a heat-resistant paper container according to claim 1, wherein the thermosetting paint is an epoxy-acrylic or epoxy-vinyl paint.