JPS6228225B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for industrially producing a porous molded product having non-linear long through-holes and having air permeability using a fiber web as a raw material. [Prior Art] Conventionally, general-purpose porous sheets have been molded by the following representative method for molding thermoplastic composite boards. (1) Male and female molding method, (2) Slip molding method, (3)
Pressure forming method (4) Vacuum forming method Among these, the vacuum forming method (4) above is the simplest and most productive from an industrial perspective. However, the molding of general porous sheets such as Styrofoam is actually done by the plug-assist method, which is a type of vacuum forming method, and the direct method is difficult to mold because the air permeability is so good. is the actual situation. On the other hand, general-purpose film sheets are mainly formed by the methods (3) and (4) above, and can be easily formed by direct vacuum forming. In other words, vacuum forming methods include (A) direct method, (B) drape molding method, (C) air slip method, (D) snapback method, (E) plug assist method,
(F) There are air action methods, methods, etc., but among them, the direct method is the most advantageous method because it is very simple to operate, low in cost, and has high productivity. [Problems to be solved by the invention] Under such circumstances, if there is a new material sheet that has an air permeability that is intermediate between a film sheet and an existing porous sheet and can be vacuum formed by a direct method,
It is industrially very advantageous. Therefore, the present inventors conducted extensive research on a method for producing porous molded products through a porous sheet that is easy to vacuum form using a direct method and has non-direct through holes, and as a result, the present invention was developed. It has been reached. [Means for Solving the Problem] That is, the present invention involves gripping all ends of a multilayer laminate of fibrous webs mainly composed of thermoplastic fibrous polymers and subjecting them to non-contact heat treatment under specific conditions to form pores. Production of a porous molded product made of a nonwoven structure, characterized by forming a porous sheet and then vacuum forming the porous sheet to obtain a molded product with an apparent density of 0.20 to 0.99 g/cm ³ It's a method. The method of the present invention will be explained in detail below. Polymers forming the thermoplastic fibrous polymer in the method of the present invention include thermoplastics such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, fluorine resin, acrylic-styrene copolymer resin, polycarbonate, polyacetal, nylon, polyester, and polyurethane. It is a general term for single polymers or mixtures thereof, and is not particularly limited, but polyolefin-based, nylon-based polymers, various elastomers, etc. are preferable because they have less strength loss after thermal melting. These polymers may contain additives such as matting agents, colorants, stabilizers, etc., if necessary. Furthermore, the fiber web used in the method of the present invention is made from a film-like material having numerous discontinuous cracks in the longitudinal direction by the burst fiber method previously proposed by the present inventors in Japanese Patent Publication No. 49-18508. In a two-dimensional fiber structure, the distribution of fiber diameter (μ) is
A web containing a fiber structure having a standard deviation of 6.0 to 12.0 and having a randomly irregular cross-section of the fibers is suitable, but a web consisting of short fibers or long fiber filaments may also be used. It is desirable for the web to be as uniform as possible, and fibers with irregular cross sections are obtained by laminating fibrillated sheets with numerous discontinuous cracks in the longitudinal direction and extending them in the width direction, which are obtained by the method described later. It is most desirable to use a reticulated fiber web consisting of: The fiber web multilayer laminate in the method of the present invention is a structure formed by laminating multiple layers of the aforementioned fiber webs, and in order to obtain a uniform porous film, it is better to laminate at least as many layers as possible. good. The pore size distribution of the non-linear through-holes of the porous molded product obtained by the method of the present invention depends on the fiber diameter of the fibers of the laminate, and when using a web of thin fibers with a fiber diameter of 10 μm or less, the The pore size in the product becomes small, and when a fiber web having a fiber diameter of about 10 to 30 μm is used, the pore size becomes large. In this way, the pore size in the molded product is closely related to the thickness of the fibers that make up the multilayer laminate, and if fiber aggregates with different denier distributions are used, the pore size of the molded product will also be random. Become something. As mentioned above, the fiber diameter (μm) distribution of the main fibers of the fiber web used in the method of the present invention is suitably one with a standard deviation (σ) of 6.0 to 12.0. When fiber webs with different finenesses are laminated so that the denier tends to increase in the thickness direction, a porous molded article with pore diameters varying in the thickness direction of the molded article can be obtained. Furthermore, when a multilayer laminate of fibers with different softening points is heat-treated and molded, the part made up of fibers with a low softening point completely dissolves and loses its fiber form, while the part made up of fibers with a high melting point disappears. Some portions do not completely dissolve, and some remain in the form of fibers, which prevents the strength of the porous molded product from deteriorating and exhibits curved heat deformability. According to the method of the present invention, by using a multilayer laminate of fibers having different deniers and softening points,
A porous molded article with a suitable pore size distribution is obtained. The porous molded article made of a nonwoven structure, which is an object of the present invention, holds a multilayer laminate of fiber webs mainly composed of a thermoplastic fibrous polymer, while sandwiching all the ends thereof, and at least 30% by weight of the polymer. % is melted by non-contact heat treatment under the conditions described below, and then applied to a mold for the desired molded product and vacuum-formed. Conventionally, it is well known that thermoplastic fiber webs are fused using heated rollers etc. to form non-woven fabrics, but the melting in the method of the present invention is different from fusion for forming non-woven fabrics. , a non-contact heat treatment is performed without applying external pressure to dissolve at least 30% by weight of the fibrous polymer, partially losing the so-called fiber morphology, forming a porous sheet, increasing the apparent density, and forming a non-linear This makes the through hole significantly smaller. Therefore, in the method of the present invention, it is necessary to perform the non-contact heat treatment of the multilayer laminate under conditions of temperature (T° C.) and time (t minutes) that satisfy the following formula. [1/(T-Tm)]≦t≦[50/(T/Tm)] [However, t is the non-contact heat treatment time (minutes), T is the ambient temperature of the non-contact heat treatment (°C), and 1 to 30 higher than the melting point (Tm℃) of the main component of the fiber polymer
℃ higher temperature. ] The fibrous polymer in the laminated web subjected to such non-contact heat treatment flows through the web space in a state of balance between melt viscosity and surface tension, forming a dense and complex porous structure. In the method of the present invention, the porous sheet material formed by such non-contact heat treatment is subjected to vacuum forming to form a molded product having a desired shape. Any of the direct method, drape molding method, air slip method, snap back method, plug assist method, and air action method can be used. In particular, the direct method is the simplest basic method among the various vacuum forming methods mentioned above, and is a method that can be manufactured at low cost in terms of equipment and productivity. In the method of the present invention, sufficient molding is possible without problems by such a direct method. That is, a porous sheet-like material obtained by non-contact heat treatment as described above is formed by vacuum suction on a mold for the desired molded product while the sheet-like material is still in a soft state. It is. The most important issue with the vacuum forming method is (a) how deep it can be drawn;
and (b) how much difference in wall thickness can be suppressed between the side and bottom parts. The porous sheet-like material subjected to the non-contact heat treatment under the above conditions used in the method of the present invention is not completely melted, and a small portion remains as softened fibers.
A sufficiently good molded product with large curved surface deformability and a ratio of drawing depth (H) to opening width (W) of around 0.5 can be obtained by the direct method. On the other hand, as will be described later in Examples, thickness deviation is sufficiently small and a good molded product can be obtained when the H/W ratio is around 0.3.
In addition, in the method of the present invention, a porous sheet material having an air permeability in the range of 0.1 to 200 seconds/100 c.c.-air as measured by the Gurley method is particularly desirable because it has good moldability. Next, with reference to the drawings, a method for producing a porous molded article made of the nonwoven structure of the present invention will be described using a specific example. A mixed thermoplastic polymer of polypropylene and 6-nylon is melt-kneaded using a vent-type extruder while nitrogen gas is pressurized, extruded from a slit die, and taken under high draft to form a cracked sheet 1 as shown in FIG. form the crack sheet
Approximately 500 sheets are laminated, and while overfeeding in the advancing direction, both ends are gripped and stretched in the width direction. The stretched web is pressed with a preliminary press roller installed between the belts to maintain its shape, and then non-contact. Non-contact heat treatment is performed for 20 to 30 seconds in the range of 195 to 200℃ using an infrared heater, and then the resulting porous sheet is applied to a direct vacuum forming machine. The second one with a width (W) ratio of 0.3 to 0.5
A cup-shaped porous molded product as shown in the figure is obtained. According to the research conducted by the present inventors, the molded product obtained by vacuum forming with good moldability has a high apparent density of 0.20 to 0.99 g/cm ³ . In addition, in the method of the present invention, reinforcing materials such as wire mesh and cheesecloth, additives such as activated carbon, fragrances, pigments, glass fibers, flame retardants, and gold foil are added to the multilayer laminate, and the non-contact heat treatment is performed. Molding may be performed to produce a porous molded product made of a nonwoven structure containing these materials. [Effects of the Invention] According to the method of the present invention as described above, an apparent density of 0.20 to 0.99 g/cm ³ can be obtained by simple direct vacuum forming.
It is possible to produce a porous molded product with good quality. The porous molded product made of the nonwoven structure of the present invention can be used, for example, in the field of clothing such as hats, art flowers, curved cores for clothing, brassiere cups, confectionery mats, plates, eating and drinking pads, etc. Food products such as trays, interior materials for lunch boxes, food packaging materials, packaging materials for fresh produce, agricultural and horticultural products such as flowerpots and seedling containers, speaker cones, parts cases, air-permeable lining materials for aquariums, etc. Examples include the industrial field. [Example] Hereinafter, the present invention will be described in detail by giving examples. In the examples, "parts" means "parts by weight." Example A thermoplastic polymer mixture of 70 parts of polypropylene and 30 parts of 6-nylon was extruded from a slit die using a vented extruder while nitrogen gas was being pressurized and taken off at a high draft to obtain a cracked sheet (A). Similarly cracked polypropylene sheet (B)
I got it. Next, the cracked sheets (A) and (B) were laminated alternately in the same direction so that the total number of laminated sheets was 500, and the fibrous material was overfed in the direction of travel while being overfed in the width direction. The fiber web was spread to form a uniform fiber web, the shape was maintained using a hot press roller, and the fiber web was wound up as a nonwoven sheet with a basis weight of 120 g/m ² . Subsequently, the nonwoven sheet is transferred between an infrared heater, heat-treated at a temperature of 195 to 200°C for 30 seconds, and immediately placed in an adjacent vacuum forming machine to form a cup-shaped porous molded product by direct method and drape method. Obtained. The product quality of the molded product was good as shown in the table below.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a sheet having numerous discontinuous cracks in the longitudinal direction, which is an example of the raw material for the method of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of a porous molded product produced by the method of the present invention, and 2 is a molded product;
3 shows the cross-sectional opening of the non-linear through hole, and 4 shows the side crack of the non-linear through hole.

Claims (1)

[Claims] 1. Conditions that satisfy the following formula so that at least 30% by weight of the polymer melts while gripping all ends of a multilayer laminate of fibrous webs mainly composed of thermoplastic fibrous polymers: By non-contact heat treatment and then vacuum forming, the apparent density is 0.20 to 0.99.
A method for producing a porous molded article made of a non-woven structure, characterized in that the molded article has a particle size of 3 g/cm ³ . [1/(T-Tm)]≦t≦[50/(T-Tm)] [However, t is the non-contact heat treatment time (minutes), T is the ambient temperature of the non-contact heat treatment (℃), and 1~ than the melting point (Tm℃) of the main component of the fibrous polymer
The temperature will be 30℃ higher. ] 2 The multilayer laminate of the fiber web has a denier and/or
Alternatively, the method for producing a porous molded article made of a nonwoven structure according to claim 1, which is obtained by laminating two or more types of fiber webs having different softening points. 3. Claim 1, in which the fibrous web is made of a mixture of two or more thermoplastic polymers having different melting points.
A method for producing a porous molded article comprising the nonwoven structure described in 1.