JPS5917933B2 - Manufacturing method of molded body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a molded article from a sheet-like material by a press molding method, and more specifically, a method for manufacturing a molded article from a sheet-like material by a press molding method, and more specifically, a method for manufacturing a molded article from a sheet-like material by a press molding method. The present invention relates to a method for continuously and inexpensively manufacturing a molded article having deep drawing, such as a paper cup, and having excellent water resistance and hot water resistance, using a sheet made of such a sheet.

In order to produce a molded product that is water resistant and hot water resistant, cellulose fibers are mixed with fibrous or powdered thermoplastic synthetic resin, and molded by hot pressure molding at a temperature higher than the melting point of the thermoplastic resin. Methods for obtaining bodies are known.

However, with this method, the synthetic resin mixed into the paper during molding melts and the strength of the sheet decreases, making the sheet more likely to break.Therefore, there is a limit to deep drawing, and it is difficult to obtain a molded product with deep drawing. It was difficult. In order to improve this drawback, various methods have been proposed in which the sheet is pretreated to improve its moldability and then molded.

For example, as seen in Japanese Patent Publication No. 45-4716, a mixed slurry of pulp and thermoplastic synthetic resin powder is preformed into a desired shape using the pulp molding method, and then heated and pressed to melt the synthetic resin powder. Resin and pulp fiber 5
A method of forming a container body by cross bonding with fibers, or a method of forming a sheet body from a mixed slurry of natural pulp and synthetic pulp as seen in Japanese Patent Publication No. 51-22512, and a wet state of this sheet body: After preforming the material in
9 methods for carrying out prescribed heat compression molding,
1546 and Japanese Patent Publication No. 52-130772, a method in which a sheet made of a mixed slurry of natural pulp and synthetic pulp is given two-dimensional wrinkles or wavy bends in advance and then subjected to hot-pressure molding; - Seen in issue 281425
When heat-pressing molding paper mixed with vegetable fibers and polyolefin synthetic fibers, there is a method of heat-pressing molding using a tension material on the tensile stress side, and a method of combining paper with wood pulp as shown in JP-A No. 52-25107. This method involves pre-pressing a sheet made of a pulp mixture at 150 to 2000 DEG C. to reduce the sheet thickness by 30 to 50%, punching out the compressed sheet into a desired shape, and then hot-pressing the sheet. However, it has been found that these methods also have the following drawbacks. '51) All of these methods increase the number of steps and require complicated operations, resulting in poor work efficiency.

■) In both cases, heat and pressure molding is carried out at a temperature higher than the melting point of the synthetic resin mixed into the final paper, so the resin inevitably melts and sticks to the press mold. , it is necessary to apply it to the mold.

Even if this makes it possible to prevent adhesion, the cost of using a mold release agent increases, and it is almost impossible to achieve a permanent mold release effect, so mold release treatment must be performed from time to time, reducing workability and productivity. significantly decreases Furthermore, when the molded body is used in a food container, various problems regarding food hygiene may occur. ) Even if a highly precise mold is used, it is difficult to uniformly apply heat and pressure treatment to the molded product, making it difficult to uniformly express the properties of the mixed resin throughout the molded product. becomes.

For example, the water resistance may be insufficient in some areas, or the paper may become transparent in some areas due to the paper's fading phenomenon and the transparency effect of the resin, resulting in poor appearance. ) When the sheet is exposed to high temperature and pressure, the pulp and synthetic resin deteriorate, yellowing, and becoming brittle with no impact resistance.

The present invention relates to a method for producing a novel molded article that improves the drawbacks of the prior art, and its gist is that 5 to 40% by weight of a fiber blend mainly composed of cellulose fibers is
A sheet made by adding fibrous or powdered thermoplastic synthetic resin is heat-treated in advance at a temperature higher than the melting point of the thermoplastic synthetic resin and without pressure, and the thermoplastic synthetic resin is made into a fiber compound. After melting and adhering the sheet to
The purpose is to mold under heat and pressure within the temperature range of the melting point.

The cellulose fiber-based fiber composition of the present invention is wood cellulose fiber, non-wood fibers such as straw, bamboo, esparto, hemp, mitten, and linta, as well as inorganic fibers such as asbestos and glass, as appropriate. It means a mixture.

Thermoplastic synthetic resins are thermoplastic cellulose derivatives,
Waxes, polyvinyl chloride, polyvinyl acetate, polystyrene, polyolefin, polyamide, polyester,
Means polyacrylates and copolymers thereof. In addition, fibrous or powdered thermoplastic synthetic resins include synthetic fibers obtained by spinning methods, so-called synthetic pulps obtained by drawing methods, polymerization methods, flashing methods, solution methods, etc., and physical pulverization. Refers to resin powder or synthetic resin dispersion obtained by this method. The melting point of thermoplastic resin is 1
If the temperature is below 00°C, the boiling resistance will decrease, and if the temperature is above 170°C, the wood pulp will easily deteriorate during molding. Therefore, in the present invention, the melting point of the thermoplastic resin is 100°C to 1.
Preferably, the temperature is 70°C.

The temperature during molding is set by heating the mold to a predetermined temperature; in this case, both or one of the male and female molds may be set to a predetermined temperature. The amount of fibrous material and powder added to the thermoplastic synthetic resin is such that the resin melts during heat treatment and has a certain level of strength, water resistance, boiling resistance, water vapor permeability, cold resistance, etc. that meets the purpose of use. It is necessary to add it in an amount that can bring out various properties, and the range of addition is 5 to 40% by weight based on the fiber blend. If necessary, auxiliary materials for paper manufacturing such as fillers, paper strength enhancers, and sizing agents may be used in combination with the fiber composition mainly composed of cellulose fibers. Next, in order to explain the present invention in more detail, the circumstances that led to the present invention will be described.

Assuming that the press molding method uses a sheet-like material such as paper to produce a molded object with deep drawing in the shape of a small tap using male and female molds, the sheet will be drawn into the female part by the male part of the mold. When the sheet is stretched, there are parts where it is stretched and parts where it is compressed, but in this case, if the sheet is stretched beyond its breaking elongation, tearing occurs at those parts.

In other words, if the strength of the sheet is greater than the stress during squeezing, the sheet can be molded without being destroyed. The present inventors believe that the reason why a sheet made by mixing thermoplastic resin powder or fibrous material with cellulose fibers is extremely poor in moldability is that the strength of the sheet itself is originally low, and that the reason for the fact that the strength of the sheet itself is originally low, and that It has been found that this is because the strength of the thermoplastic resin decreases as the resin softens and melts due to the application of heat exceeding the melting point of the thermoplastic resin.

In order to improve the strength of a sheet made by mixing cellulose fiber with thermoplastic resin powder or fibrous material, the sheet is treated at a temperature higher than the melting temperature of the thermoplastic resin without pressure,
The resin may be melted and adhered to the intertwined portions of cellulose fibers. For example, 80 parts by weight of NBKP pulp is beaten to 30% SR, and polyethylene synthetic pulp (trade name: SWP) is added to this.
l Manufactured by Krawanzeraback, melting point approx. 135°C) at 20°C.
The tensile strength of a sheet made into a sheet of 3509/wl by adding parts by weight was 21.51<g when measured by JISP-8113 method.
/151Lm, but when this sheet is heat treated for 1 minute in a hot atmosphere of 160°C above the melting point of the synthetic pulp and under no pressure, 32.51<f! /15mm Same as above. This tendency is observed in polyethylene resin powder (melting point approximately 1
It was also confirmed that the results were almost the same when the same amount of 35°C) was added. Comparing the moldability of the heat-treated sheet and the untreated sheet, it was confirmed that the moldability of the heat-treated sheet was clearly improved. The heat treatment effect of the internally added thermoplastic resin cannot be expected by drying in a normal paper machine. Typical heat treatment methods include the aforementioned method of treating the sheet in a hot atmosphere without pressure, and the method of treating the sheet with a hot pressure roll or hot plate press. The inventors of the present invention conducted a comparative study of the two, and found that sheets processed by hot pressure rolls or hot plate presses have major drawbacks as described below.

In other words, when a sheet processed with a hot pressure roll or hot plate press is cooled and then punched into a desired shape and hot-press molded, a blistering phenomenon occurs between the paper layers of the sheet, making it difficult to obtain a good molded product. It was difficult to obtain. The reason for this is that when the sheet is processed with a hot pressure roll or hot plate press, the air permeability of the sheet is significantly reduced, and there is no place for the water vapor and air generated from the moisture contained inside the paper layer to escape during hot pressure forming. This is thought to be due to the destruction of the layer. On the other hand, when the sheet is processed in a hot atmosphere and without pressure, the air permeability is rather improved, so it can be molded without causing blistering. In this way, the sheet is treated in a hot atmosphere above the melting point of the mixed thermoplastic resin and without pressure to improve its strength (simultaneously imparting water resistance and hot water resistance), and then punched into the desired shape. Perform hot pressure molding.

At this time, 400C below the melting point of the thermoplastic resin mixed with the molding.
By carrying out the process in the warm range from ~ to the melting point, it is possible to prevent the pulp and synthetic resin from deteriorating and becoming brittle with no impact resistance, and the strength of the sheet is less likely to decrease due to heat. It is possible to perform deep drawing molding. In this case, the problem is whether the strength and shape of the molded product are maintained after molding, but in the above temperature range, the mixed resin is softened, so during hot pressure molding, the resin and the fibers It was confirmed that the molded product had adhered to each other and the strength and shape of the molded product were sufficiently maintained.

The experimental history that led to the present invention will be explained below.

First, the following samples were created. Sample Waterfall 1 50 parts of NBKP and 30 parts of LBKP were disintegrated, and 2 parts of polyethylene synthetic pulp (trade name SWP-E4OOl, melting point 1300C to 135C, manufactured by Mitsui Zerabak Co., Ltd.) was added to this.
A sheet of 4009/I was made using a 0-part mixed Fourdrinier paper machine using a conventional method.

Sample return 2 The above-mentioned sample 1 was subjected to heat and pressure treatment using a thermal calendar.

Heat pressure treatment is performed at a temperature of 150℃ and a linear pressure of 260kg/CT! L
The test was carried out under conditions of 1 clearance of 0.2271 Lm and 15 m/min. Sample waterfall 3 sample A6. The sample was heat-treated for 10 minutes in a hot air circulation oven maintained at 160° C. and under no pressure.

50 parts of sample Taki 4NBKP and 30 parts of LBKP were disintegrated,
This was mixed with 20 parts of polyethylene fine powder (melting point: 130-135°C, average particle size: 50-75 mesh), and a sheet of 4009/d was made using a Fourdrinier paper machine in a conventional manner.

Then, it was heat-treated for 10 minutes in a hot air circulation oven maintained at 160° C. and under no pressure. Table 1 shows the results of physical property measurements.Next, a molding test was conducted using male and female steel molds for manufacturing trays as shown in FIG.

The temperature of the mold was changed and each sample was heated to 10×12C7r.
Cut to L press pressure 45kg/CTill pressurization time 5
Molded in seconds. Table 2 shows the moldability and various performances of the molded product.
It is shown in Table-6. The results of this experiment revealed the following.

1) Sample Taki 1 breaks in the molded body in the range of 80°C to 150°C, and cannot be continuously molded.

2) Sample 7f62 blistered at 95°C to 150°C and could not be molded.

3) At a molding temperature of 80° C., the water resistance and boiling resistance of Sample Waterfall 1 are poor, and the water resistance and boiling resistance of Sample Waterfall 1 at /F6.2, /F6.3 and Waterfall 4 are slightly inferior.

4) At the molding temperature of 150℃, the sample. 46.1, A6.2,
Both Arai 3 and Taki 4 have poor continuous moldability.

From the above, samples that can be continuously molded and satisfy various performances as molded bodies are sample 7f6.3 and sample waterfall 4.
It was confirmed that the molding temperature was 95°C to 135°C.

The inventors of the present invention have repeated similar experiments by changing the type of thermoplastic synthetic resin and its addition ratio to cellulose fibers, and have found that various performances as a molded product can be improved by performing hot-pressure molding under the conditions stated in the claims. It was confirmed that continuous molding was possible. Example-1 After disintegrating 50 parts by weight of NBKP (hereinafter referred to as 8 LBKP3O parts by weight) and mixing it with 20 parts by weight of polyethylene synthetic pulp (trade name SWP-E4OO manufactured by Mitsui Zerabakku Co., Ltd.) , 5 parts by weight of a sizing agent (trade name Size Pine E manufactured by Arakawa Chemical Industry Co., Ltd.), SB
5 parts by weight of R Latex (trade name: Nipole 2507 manufactured by Nippon Zeon Co., Ltd.), 5 parts by weight of aluminum sulfate, and 0.5 parts by weight of polyacrylamide (trade name: Polyatalon GT manufactured by Hamano Industries Co., Ltd.) were added. Then, a sheet of 4009/m'' was made using a Fourdrinier paper machine in a conventional manner.

This sheet was treated in a hot atmosphere of 150 to 160 C for 10 minutes without pressure, and then cooled and treated with 10×12 cIn.
Punched into the corner. This punched sheet was molded using the mold shown in Fig. 1 at a mold temperature of 120°C and a press pressure of 45 kg/~.
Continuous molding was performed with a pressurization time of 5 seconds. The molded product obtained satisfied the above-mentioned properties such as water resistance and boiling resistance, and had good moldability. As described above, the present invention has made it possible to produce a molded product having deep drawing and excellent water resistance and boiling resistance.

Since this molded product has the above-mentioned performance, it can be used for food containers, trays, instant noodle cups, etc. In addition, it can provide appropriate water vapor permeability and the contents will not become steamy, so it can be particularly suitably used for containers for boiled rice and the like.

[Brief explanation of the drawing]

FIG. 1 shows a steel mold for manufacturing trays.

Claims (1)

[Claims] 1 5 to 40 for fiber blends based on cellulose fibers
A sheet made by adding fibrous or powdery material of a thermoplastic synthetic resin in an amount of % by weight is heat-treated in advance at a temperature higher than the melting point of the thermoplastic synthetic resin and under no pressure. After melting and adhering to the fiber compound, the sheet is cooled and punched into a desired shape at a temperature below the melting point of the thermoplastic resin.
A method for producing a molded body, characterized by hot-pressure molding in a temperature range from 0°C to the melting point.