JP2006299441A - Nonwoven fabric for thermoforming - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonwoven fabric for thermoforming that comprises the first thermoplastic staple fiber having a high melting point and the second thermoplastic staple fiber having a low melting point and can at least fusion-bond in the thermoforming and can achieve free thermoforming process scarcely causing shrinkage during the thermoforming. <P>SOLUTION: The first high melting thermoplastic staple fiber such as PET and the second low melting staple fiber such as PP that can achieve the fusion bonding at least in the thermoforming are mixed substantially uniformly and bonded to prepare the thermoforming type nonwoven fabric. As the second thermoplastic staple fiber such as PP, is used the one having a thermal shrinkage of about less than 2%, preferably less than 1.5% according to JIS-L105. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-woven fabric for thermoforming that hardly undergoes shrinkage during thermoforming. More specifically, the first thermoplastic short fiber having a high melting point and the second thermoplastic short fiber having a low melting point that melts during thermoforming are uniformly mixed. The present invention relates to a non-woven fabric for thermoforming in which short fibers are bonded in a state.

  Here, PP short fibers are mainly used as the second thermoplastic single fiber having a low melting point, and automotive molded products such as fender liners (see FIG. 1) and floor mats are thermoformed (including hot-pressure molding). However, the present invention is not limited to this.

  As a molding material in the case of thermoforming an automobile molded product or the like, a nonwoven fabric mainly composed of thermoplastic short fibers has been frequently used from the viewpoint of soundproofing and interference.

  As the nonwoven fabric, thermoplastic fibers are joined by heat crosslinking (including vulcanization) using an aqueous emulsion adhesive (binder) such as SBR (styrene rubber) latex or NBR (acrylic rubber) latex. Is frequently used. And the said nonwoven fabric was supplied to the thermoforming (processing) process, and was made into molded articles for motor vehicles, such as a floor carpet and a fender liner.

  In the thermoforming process, the thermoplasticity of the thermoplastic short fiber is mainly used. Since the binder is a rubber component, the non-woven fabric, which is a molding material, has low rigidity at the joint and can be easily heat-formed.

  These automobile molded products are not discarded but recently requested to be recycled after the end of their useful life.

  And recycling is normally performed by heating to the melting temperature of the short fiber (skeleton fiber) which forms a nonwoven fabric, and making it a repellet (recycled pellet) like other plastic waste. During this heating, the crosslinked SBR / NBR, which is an adhesive component, is not thermally melted but is pyrolyzed and carbonized, and remains in the melt as residue (soot: carbon). This carbide adversely affects the colorability and physical properties and lowers the recyclability.

Although it does not affect the patentability of the present invention, for example, Patent Document 1 (technology related to polypropylene-based nonwoven fabric is described), Patent Document 2 (technology related to polyester-based nonwoven fabric with small thermal shrinkage is described). .) Etc. Moreover, there exists patent document 3 which concerns on the application of the same applicant as this prior art document regarding a molded article nonwoven fabric.
JP 2004-44030 A (summary etc.) No. 2002-07805 (summary etc.) JP 2004-270089 A (summary etc.)

  In order to solve the above problems, the present inventor, instead of the joining method using an emulsion adhesive at the time of thermoforming, a specification that does not use rubber latex, for example, a polyester fiber is a first thermoplastic fiber (skeleton fiber) It is conceivable that PP short fibers are used as the second thermoplastic fibers (adhesive fibers), and finally the PP short fibers are used as the adhesive fibers.

  That is, when performing thermoforming using a nonwoven fabric containing PP short fibers, the PP short fibers are melted and penetrated between the fibers forming the nonwoven fabric to bond the fibers within the nonwoven fabric ( And the function of maintaining the form imparted to the nonwoven fabric is exhibited.

  However, it has been found that in a nonwoven fabric using ordinary PP short fibers, excessive shrinkage occurs in the nonwoven fabric molded product in the molding process. That is, it has been found that a nonwoven fabric containing PP short fibers can be used as a molding material only by a special molding method that can forcibly limit thermal shrinkage.

  Such a special molding method not only requires a special molding machine, but also makes it difficult to mold into a free shape (especially when it becomes a complicated shape). Such a problem is considered to be unavoidable due to the inherent thermal properties of PP fibers.

  In view of the above, the subject (object) of the present invention is formed of a high-melting-point first thermoplastic short fiber and a low-melting-point second thermoplastic short fiber that exhibits a melt-bonding (joining) action at least during thermoforming. In the non-woven fabric for molding, there is almost no shrinkage during thermoforming, and free thermoforming is possible.

  The non-woven fabric for thermoforming according to the present invention solves the above problem (purpose) by the following configuration.

  It should be noted that the “about” given before the numerical limitation does not obscure the numerical range including the claims, and those skilled in the art, when touched by it, will recognize the constitution of the invention (invention). Specific matter) can be recognized as clear. This is because the numerical limitation in the invention (claims) merely indicates an index of a technical range that can be implemented, and does not require strictness in a mathematical sense.

The first short thermoplastic fibers having a high melting point and the second short thermoplastic fibers having a low melting point exhibiting a melt bonding (bonding) action at the time of thermoforming are bonded to each other in a substantially uniform mixed state. A non-woven fabric for thermoforming,
The second thermoplastic short fiber is characterized by exhibiting a heat shrinkage rate (JIS-L1015) of about 2% (preferably about 1.5%) or less.

  By using a second thermoplastic short fiber (melted fiber) having a predetermined shrinkage ratio or less, in the thermoforming (processing) step, almost no heat shrinkage occurs in the molded product as in the examples described later.

  In the above, when the melting point difference between the first thermoplastic short fiber (skeleton fiber) and the second thermoplastic short fiber (molten fiber) is 20 ° C. (desirably 25 ° C.) or more, the thermoformability is improved. . That is, if the difference in melting point is small, it becomes difficult to distinguish the action as a skeletal fiber and a molten fiber, and strict temperature control is required during thermoforming.

  Usually, it is desirable that the second thermoplastic short fiber (molten fiber) is a polypropylene (PP) short fiber. This is because normal (general-purpose) PP has a relatively low melting point (165 to 173 ° C.), has heat-resistant adhesiveness, and is balanced.

  When the second thermoplastic short fiber is a PP short fiber, the first thermoplastic short fiber to be combined is preferably a polyester short fiber. This is because polyester short fibers have a predetermined temperature difference (about 20 ° C.) between the softening point and the melting point, and are excellent in thermoformability.

  The mixing mass ratio of the first thermoplastic short fiber and the second thermoplastic short fiber is desirably the former / the latter≈10 / 90 to 80/20. If the amount of the second thermoplastic short fiber that becomes the adhesive fiber is too small, it is difficult to ensure the form retainability of the thermoformed product. This is because a bonding failure occurs due to a shortage of adhesive fibers (second thermoplastic short fibers) between the first thermoplastic short fibers which are skeleton fibers. On the other hand, if the second thermoplastic excess is obtained, it is difficult to ensure the properties (heat insulation, soundproofing, etc.) and texture of the nonwoven fabric. The ratio of the skeletal fibers decreases, the occupation ratio of the melted resin-bonded adhesive fibers in the thermoformed product increases, and the texture becomes close to that of a plastic molded product (resin molded product).

  In this molding nonwoven fabric, it is desirable that the short fibers are joined to each other by needle lock (needle punching) joining. Other mechanical joints (for example, water needle: water entanglement method, spin race method) may be used, but the needle lock is more suitable for thermoforming by controlling the needle density and the number of driving. It is easy to obtain a non-woven fabric for molding having a form retaining property suitable for handling at the time of molding.

  The non-woven fabric for molding of the present invention may be a pre-melt bonded treatment product in which the second thermoplastic short fibers are partially melted and bonded.

  The technical scope of the present invention extends to thermoformed products (automobile parts) such as fender liners and floor carpets, which are thermoformed with the thermoforming nonwoven fabric having the above-described configurations.

  Further, the present invention also extends to a method for manufacturing a molded product in which a molded product is manufactured by thermoforming using the thermoforming nonwoven fabric having the above-described configurations.

  And the structure of the nonwoven fabric for thermoformed articles of the more desirable embodiment of the present invention is as follows.

A non-woven fabric for thermoforming, in which short polyester fibers and PP short fibers having a heat shrinkage of about 1.5% or less are bonded in a substantially uniform mixed state.
Their mixing mass ratio is characterized by the former / the latter≈10 / 90 to 80/20.

  Hereinafter, the present invention will be described in detail based on embodiments.

  In the present specification, the “molding nonwoven fabric” refers to a nonwoven fabric used when a nonwoven fabric is supplied to the molding process and subjected to thermoforming. And this nonwoven fabric itself has a form-retaining property, and needs to be heat-set (fixed form) into a free shape by molding.

  The first thermoplastic short fiber (skeleton fiber) used as the skeleton fiber in such a nonwoven fabric is not particularly limited as long as it has heat characteristics that are set by heat at the time of thermoforming but are not completely melted. For example, when the thermoforming temperature (mold temperature) is 160 to 200 ° C., artificial fibers (particularly synthetic fibers) such as polyester, nylon, high melting point PP, and rayon, and natural fibers such as jute, kenaf, and sisal can be used. In addition, composite fibers (composite yarns) such as bimetal type, sheath-core type, and kidney type, in which at least part of the outer side of the short fiber cross section is formed of the same thermoplastic resin material as the adhesive fiber, can also be used.

  Among these, polyester fibers (PET, PBT) that are excellent in thermoformability and relatively small in thermal deterioration during recycling are preferable.

  In addition, the second thermoplastic short fiber forming the adhesive short fiber (melted short fiber) is substantially completely melted at the time of thermoforming, and has an effect of adhering the skeleton short fibers to each other. If L1015) is about 2% or less, desirably about 1.5% or less, there is no particular limitation. For example, polyethylene (PE), polypropylene (PP), low melting point polyester (design melting temperature: 110 ° C., 120 ° C., 130 ° C.) can be mentioned. Here, PP is desirable. In the case of PE, the heat resistance is poor, and in the case of a low melting point polyester, it is expensive. The general-purpose PP fiber has a heat shrinkage rate (JIS-L1015) of around 3.0%.

  The mixing ratio (mass ratio) between the skeleton short fibers and the bonded (melted) short fibers is the selected fiber and the required shape retention / nonwoven fabric properties (texture and functionality (heat insulation, soundproofing, cushioning, etc.)) Varies by That is, from the standpoint of form retention (rigidity), the short adhesive fibers are many, and from the viewpoint of nonwoven fabric, the short skeleton fibers are many.

  In the mass mixing ratio of the second thermoplastic short fiber (adhesive short fiber) / first thermoplastic short fiber (skeleton short fiber), when the adhesive short fiber is PP and the skeleton short fiber is PET, it is generally about 10 / 90 to 80/20, more generally about 20/80 to 70/30, and most typically about 30/70 to 60/40. In actual use, the mixing ratio may be determined in consideration of the basis weight of the nonwoven fabric and the thermal characteristics of the skeleton short fibers.

  If the PP short fibers are too small, the shape retention of the molded product obtained is lowered and the object of the present invention cannot be achieved. On the other hand, if the PP short fibers are excessive, a molded product obtained by molding may lose the texture as a nonwoven fabric and become a resin molded product.

  The PP short fibers used in the present invention have a heat shrinkage of about 2.0% or less, preferably about 1.5% or less, more preferably about 1.3% or less. Need to use. When the thermal contraction rate of the PP short fibers exceeds about 1.5% (especially about 2.0%), the nonwoven fabric itself is greatly shrunk during the molding process as in the case of the conventional nonwoven fabric, so that the molding process is not performed. It becomes difficult to achieve the object of the present invention.

  For the PP short fibers having such physical properties, a conventionally known PP polymer can be used as the polymer. However, when the polymer is melt-spun and subjected to a drawing process, the draw ratio is set to a normal one. It can be manufactured by making it much lower. That is, the draw ratio is set in the range of about 130 to 180%, desirably about 140 to 160%. From the viewpoint of a low heat shrinkage rate, it is desirable that the draw ratio is relatively low. However, if the draw ratio is too low, it becomes difficult to obtain a predetermined strength in the fiber, and fiber breakage is likely to occur in the blending process and the carding process. For this reason, the heat shrinkage rate is appropriately set within the above range from the balance of the required fiber strength.

  PP short fibers used in the present invention permeate between fibers of other first thermoplastic short fibers (polyester short fibers: skeletal fibers) that melt during molding to form a nonwoven fabric, and bond the skeleton fibers together ( It functions as a resin for holding the shape after the molding process is completed.

  For this purpose, it is necessary to carry out the molding process at a temperature higher than the melting temperature of PP, and it is required that the nonwoven fabric itself does not shrink due to PP short fibers despite such a high temperature process. . It is not publicly known that PP short fibers having a low shrinkage (thermal shrinkage of about 2.0% or less, preferably about 1.5% or less) satisfy such a requirement, and the present inventors have found out as a result of trial and error. It is.

  The fineness and cut length of the first and second thermoplastic short fibers forming the skeletal fiber and the molten fiber differ depending on the required properties for the nonwoven fabric, but considering the card's passability when manufacturing the nonwoven fabric. Fineness: about 3.3 to 11.0 dtex, cut length (staple length): about 51 to 76 mm.

  Such a short fiber mixture (nonwoven fabric raw material) containing PP short fibers is supplied to a blending process by a normal method, and further formed into a web through a fluffing process. Thus, the PP short fibers are uniformly dispersed in the web. Subsequently, a short fiber sheet can be formed by a cross layer process, and a nonwoven fabric can be manufactured using this short fiber sheet.

  In order to manufacture the nonwoven fabric, known methods such as a method of processing using a water needle (flowing water entanglement method, spin race process) and a method of processing using a metal needle (needle needle) are exemplified.

  In the nonwoven fabric by the processing method using a water needle, it is difficult to obtain the elongation of the nonwoven fabric during the molding process, and molding may be difficult depending on the shape of the molded product (when the radius of curvature is small).

  On the other hand, a non-woven fabric produced by a processing method using a needle needle is a preferred embodiment particularly as a non-woven fabric for molding because moderate elongation and shape retention are obtained.

  The thermoforming nonwoven fabric 12 thus prepared is made into a molded product (fender liner) 2 as shown in FIG. 1 through the following thermoforming process (see FIG. 2). In FIG. 1, 4 is a reinforcing rib, and 6 is a bolt hole for mounting the vehicle body.

  After heating with a thermal infrared heater (electric heater) 14 or the like until the surface temperature reaches the set temperature, it is continuously supplied between the female and male molds 16 and 18 and closed for a predetermined time. After cooling, open and release the mold.

  In the above, each working condition varies depending on the types of first and second thermoplastic short fibers, the mixing ratio, the thickness of the molded product, and the like. For example, when the first thermoplastic fiber / second thermoplastic fiber = general-purpose PET / PP (50/50), the fiber surface heating temperature: 170 to 200 ° C., mold closing time: 30 to 60 s, and in-mold water cooling.

  In addition, the nonwoven fabric 12 for shaping | molding may be what was called a pre-melting | adhesion processed material which left by performing heat processing combining the electric heater, the microwave heating, or the hot air heating individually or in combination suitably. For example, in the case of the above-described PET / PP combination, the working conditions of this pre-melt adhesion treatment vary depending on the heating means and the type / mixing ratio of the fibers, but the ambient temperature: about 180 to 200 ° C. × treatment time: about 30 s 5 min. By this pre-melt bonding treatment, that is, the short fibers constituting the nonwoven fabric are bonded to each other by melting the PP short fibers contained in the nonwoven fabric to some extent, thereby improving the handleability of the molding nonwoven fabric and reducing the time of the heat molding process. Shortening can also be achieved.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  The method for measuring the heat shrinkage rate according to the present invention was performed in accordance with the method described in JIS-L1015. At this time, the test conditions were a gripping interval: 25 mm and a processing temperature: 145 ° C. × 5 min.

<Example 1>
As a short fiber used as a raw material of the nonwoven fabric, a commercially available polyester short fiber (PET: 6.6 dtex × 64 mm) is used at a ratio of 60% by mass of the total short fiber, and a heat shrinkage rate (JIS-L) is 1.3%. The low heat-shrinkable PP short fibers (6.6 dtex × 64 mm) are used in a proportion of 40% by mass of the total short fibers and fed to the cotton blending process to mix both the fibers. A web is formed by feeding, the web is laminated with a cross layer to form a short fiber sheet, and then a non-woven fabric subjected to normal needle punching is pre-bonded under conditions of ambient temperature: 200 ° C. × time: 4 min. To form a nonwoven fabric for molding.

  The molding nonwoven fabric was cut into a free state and subjected to a heat shrinkage test under conditions of dry heat of 190 ° C. × 5 min, but no shrinkage was observed.

  Also, using the same non-woven fabric for molding, it was supplied to a normal thermoforming process and heated with a far-infrared heater until the surface heating temperature was 190 ° C., and then molded with a mold. This problem did not occur at all, and a predetermined molded product was obtained. Here, the molding process conditions were a mold clamping time: 40 s and water cooling in the mold.

<Comparative Example 1>
As short fibers used as a raw material for the nonwoven fabric, the same polyester short fibers as used in Example 1 (6.6 dtex × 64 mm) were used in a proportion of 60% by mass of the total short fibers, and commercially available normal PP short fibers. A nonwoven fabric for molding was obtained in the same manner as in Example 1 except that (6.6 dtex × 64 mm, heat shrinkage rate: 2.5%) was used at a ratio of 40% by mass of all short fibers. When this non-woven fabric was heat-treated under the same conditions as in Example 1, a shrinkage of about 50% occurred as the shrinkage rate, and could not be used as a non-woven fabric for molding.

  The nonwoven fabric for molding of the present invention obtained in this way can be widely used as a member for vehicles, and is particularly suitable for interior and exterior products for automobiles that require soundproofing / sound insulation such as fender liners and floor carpets. Application expansion is expected.

The perspective view and model sectional view of a fender liner to which the present invention is applied. FIG. 2 is a model cross-sectional view when the fender liner of FIG. 1 is molded.

Explanation of symbols

12 ... Nonwoven fabric for thermoforming 14 ... Far infrared heater 16 ... Male (upper)
18 ... Female mold (lower mold)

Claims (9)

The first short thermoplastic fibers having a high melting point and the second short thermoplastic fibers having a low melting point exhibiting a melt bonding (bonding) action at the time of thermoforming are bonded to each other in a substantially uniform mixed state. A non-woven fabric for thermoforming,
The non-woven fabric for thermoforming, wherein the second thermoplastic short fiber exhibits a heat shrinkage rate (JIS-L1015) of about 2% or less.     The nonwoven fabric for thermoforming according to claim 1, wherein the second thermoplastic short fibers exhibit a thermal shrinkage (JIS-L1015) of about 1.5% or less.   The nonwoven fabric for thermoforming according to claim 1 or 2, wherein a difference in melting point between the first thermoplastic short fibers and the second thermoplastic short fibers is about 20 ° C or more.   The nonwoven fabric for thermoforming according to claim 1, 2 or 3, wherein the second thermoplastic short fibers are polypropylene (PP) short fibers.   The nonwoven fabric for thermoforming according to claim 4, wherein the first thermoplastic short fibers are polyester short fibers.   6. The thermoforming according to claim 4, wherein a mixing mass ratio of the first thermoplastic short fiber and the second thermoplastic short fiber is the former / the latter≈10 / 90 to 80/20. Non-woven fabric.   The thermoforming nonwoven fabric according to any one of claims 1 to 6, wherein the short fibers are bonded to each other by needle lock bonding.   The non-woven fabric for thermoforming according to any one of claims 1 to 7, wherein the second thermoplastic short fiber is a pre-melt bonded product obtained by partial melting and pre-melt bonding. A non-woven fabric for thermoforming, in which short polyester fibers and PP short fibers having a heat shrinkage of about 1.5% or less are bonded in a substantially uniform mixed state.
A non-woven fabric for thermoforming, wherein the mixing mass ratio is the former / the latter≈10 / 90 to 80/20.

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