JPH0825489A - Lightweight stampable sheet excellent in expansion property and handling property - Google Patents

Abstract

PURPOSE:To improve the expansion property and handling property (touch; pricking feeling) of a lightweight stampable sheet obtained by thermally expanding a web formed from a dispersion of a reinforcing glass fiber and a granular matrix resin by a papermaking process so as to obtain predetermined thickness. CONSTITUTION:Two kinds of reinforcing glass fibers different in diameter are used and W2wt.% of a large diameter fiber and W1-wt.% of a small diameter fiber are added to a stampable sheet so that a value of W2/(W1+W2) is set to 0.3-0.7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight stampable sheet having high strength which is useful as an interior material for automobiles such as a ceiling material and a door trim.

[0002]

2. Description of the Related Art A papermaking method is known as a method for manufacturing a lightweight stampable sheet. In the papermaking method, a glass fiber having a length of 6 to 50 mm and a granular thermoplastic resin are dispersed in a surfactant aqueous solution containing fine bubbles, and a web is prepared by making the dispersion liquid on a porous support, Heat and pressure are applied to this web to produce a solidified and dense sheet (hereinafter sometimes referred to as a consolidate sheet). This sheet is heated above the melting point of the thermoplastic resin to melt the resin.
At this time, the sheet is springback of glass fiber,
Expands more than the original thickness. The expanded sheet is placed on a mold and compression molded to obtain the required shape. By adjusting the clearance of the mold during compression molding, it is possible to obtain a lightweight stampable sheet having a smaller density than the consolidate sheet. This technique is disclosed in JP-A-60-179233.

[0003]

SUMMARY OF THE INVENTION The present invention is directed to a lightweight stampable sheet obtained by the above papermaking method. Since the rigidity of a flat plate such as a panel is proportional to (elastic modulus) × (thickness) ³ , it is advantageous to increase the plate thickness in order to increase the rigidity of parts. The lightweight stampable sheet utilizes the expansion of glass fiber due to springback when heated above the melting point of the matrix resin, and is suitable for increasing the rigidity of the flat plate. However, the conventional lightweight stampable sheet obtained by the papermaking method does not expand sufficiently, so that the improvement in rigidity is insufficient.

As a method for improving the expansivity, a method of increasing the content of glass fibers, a method of increasing the fiber diameter of the glass fibers, and Japanese Patent Application No. 6-49 filed by the applicant of the present invention.
As in the invention of No. 94, a method of laminating a plurality of webs and making the glass fiber diameter of the outermost web smaller than that of the inner web can be considered. However, the method of increasing the glass fiber content lowers the moldability and makes it particularly difficult to mold a door trim that requires deep drawing. In addition, the method of increasing the diameter of the glass fiber increases the rigidity of the glass fiber itself, so that the expandability of the stampable sheet is improved, but the handling property is deteriorated, that is, the glass fiber is squeezed into the hand during handling (a tingling sensation). ) Occurs, and when the sheet is clamped at both ends and preheated at the time of molding, sagging (referred to as drawdown) occurs, and defects such as contact with the heater occur. Further, the method of Japanese Patent Application No. 6-4994 has a problem in that a plurality of webs need to be laminated, which complicates the manufacturing process.

An object of the present invention is to solve the above-mentioned problems and to provide a lightweight stampable sheet having excellent expandability and handleability and having a small drawdown.

[0006]

DISCLOSURE OF THE INVENTION According to the present invention, a dispersion is prepared by dispersing a reinforcing glass fiber and a granular matrix resin in a surfactant-containing aqueous medium in which air microbubbles are dispersed. A sheet-shaped web is prepared by making a liquid with a porous support, and after drying, heat and pressure are applied to solidify the sheet, and the sheet is heated above the melting point of the matrix resin and expanded in the thickness direction of the sheet. After that, in the lightweight stampable sheet produced by compression molding so that the density becomes smaller than the theoretical density when the porosity in the sheet is zero, the reinforcing glass fiber is composed of two kinds of different fiber diameters. When the addition amount of small-diameter fibers is W1 wt% and the addition amount of large-diameter fibers is W2 wt% in a stampable sheet made of reinforcing glass fiber, the value of W2 / (W1 + W2) should be 0.3 to 0.7. The lightweight stampable sheet excellent in expandable and handling properties characterized.

[0007]

The present invention will be described below in more detail. <Reinforcing Glass Fiber> The length of the reinforcing glass fiber is preferably 6 to 50 mm in order to obtain a sufficient reinforcing effect of the reinforcing glass fiber and to secure the moldability during molding. More preferably, it is 10 to 26 mm. If the reinforcing glass fiber is too short, a sufficient reinforcing effect cannot be obtained and the paper breaks easily in the papermaking process.
On the other hand, if the fiber length is too long, the fluidity at the time of molding is reduced, the reinforcing glass fibers are not sufficiently opened in the papermaking process, the expansion becomes uneven, and the springback effect is small.

The diameter of the reinforcing glass fiber is preferably 5 to 30 μm in order to secure the reinforcing effect and the expanding effect of the reinforcing glass fiber. More preferably, it is 10 to 25 μm. If the fiber diameter is small, sufficient expansion cannot be obtained during heating. If the fiber diameter is too large, a sufficient reinforcing effect cannot be obtained. In the present invention, when the addition amount of the small diameter fiber is W1 wt% and the addition amount of the large diameter fiber is W2 wt% with respect to the stampable sheet, the value of W2 / (W1 + W2) (hereinafter also referred to as the mixing ratio of the reinforcing glass fiber I say) is limited to 0.3-0.7.

When the mixing ratio of the glass fibers is 0.3 to 0.7, a well-balanced expansion plate having no tingling sensation, a good surface feeling and a high rigidity can be obtained. It is more preferably 0.4 to 0.6. When the mixing ratio of the glass fibers is less than 0.3, the expansion plate does not have a tingling sensation, but the rigidity is low. When the mixing ratio of the glass fibers is more than 0.7, the rigidity is high, but the tingling sensation is severe and the handling is difficult.

The diameter of the large diameter reinforcing glass fiber is preferably 20 to 30 μm, while the diameter of the small diameter reinforcing glass fiber is 5 to 20 μm.
Is preferred. More preferably, in the above range, the ratio of the diameter of the large-diameter reinforcing glass fiber to the diameter of the small-diameter reinforcing glass fiber is at least twice. In the present invention, the thick reinforcing glass fiber and the thin reinforcing glass fiber are entangled with each other, and the repulsion force (springback) of the thick reinforcing glass fiber is dispersed in the thin reinforcing glass fiber, so that the thick reinforcing glass fiber is a resin. The frequency of going outside the surface is reduced and the tingling sensation is reduced. In addition, although the diameter of the fiber is limited to two in the present invention, three or more kinds of fibers can be used within a range satisfying the idea of the present invention.

In the lightweight stampable sheet, it is preferable that the weight ratio of the reinforcing glass fiber (total weight) to the matrix resin (glass fiber / resin) is 20/80 to 70/30. An excessively small amount of reinforcing glass fiber has a small reinforcing effect. In addition, when the reinforcing glass fiber is used excessively, it is difficult to uniformly impregnate the reinforcing glass fiber bonding point with the matrix resin, which causes a decrease in strength.

The surface of the reinforcing glass fiber is optionally treated with a silane coupling agent and a sizing agent. The silane coupling agent improves the wettability and adhesiveness, and the sizing agent controls the opened state of the glass fiber. As the silane coupling agent, vinylsilane-based, aminosilane-based, epoxysilane-based, methacrylsilane-based, chlorosilane-based, mercaptosilane-based, and the like can be used. Of these, aminosilane type and epoxysilane type are preferable. As a method for treating the glass fiber with the silane coupling agent, a known method such as a dry method in which the aqueous solution of the silane coupling agent is sprayed while the glass fiber is mixed, or the glass fiber is immersed in the aqueous solution of the coupling agent can be used. The amount of silane coupling agent is based on the glass fiber
0.001 to 0.3 wt% is preferable. More preferably 0.005
~ 0.2 wt%.

If it is less than 0.001 wt%, the improvement in strength is small.
In order to improve the strength and expandability of the lightweight stampable sheet, it is desirable to open the reinforcing glass fiber into single fiber. Therefore, the reinforcing glass fiber is treated with a water-soluble sizing agent. Examples of these sizing agents include a polyethylene oxide type and a polyvinyl alcohol type. The amount of the sizing agent is 0.03 to 0.3 wt% with respect to the reinforcing glass fiber. More preferably, it is 0.05 to 0.2 wt%. 0.3 wt%
If it exceeds, it becomes difficult to open the fiber in the papermaking process.

<Matrix resin> The matrix resin which can be used in the present invention is preferably a thermoplastic resin such as polyolefins such as polyethylene and polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polyamide, polyacetal and the like. The copolymers and graft compounds and blends containing the resin as a main component, such as an ethylene-vinyl chloride copolymer, an ethylene-vinyl acetate copolymer, a styrene-butadiene-acrylonitrile copolymer, and the like. Of these, polypropylene is preferred.

The average molecular weight (Mw) of the matrix resin is 5
0000-700000 is preferable. If the Mw is less than 50,000, the melt viscosity is low and the wettability and adhesion to glass fibers are good, but the resin becomes brittle, and the mechanical properties of the lightweight stampable sheet deteriorate. If the Mw is more than 700,000, the impregnating property and the wettability at the glass fiber joint will be deteriorated and the mechanical properties of the sheet will be deteriorated. Further, the fluidity is reduced.

In order to improve the adhesiveness between the resin and the glass fiber, the matrix resin modified with a compound such as acid or epoxy can be used in combination. In the case of polypropylene, it can be modified with maleic acid, maleic anhydride, acrylic acid or the like, and those having a modifying group as an acid anhydride group or a carboxyl group are preferable. The weight average molecular weight of the modified resin is preferably 20,000 to 200,000. If it is less than 20000, the melt viscosity is low, and the wettability and adhesion to glass fiber are good, but the resin becomes brittle, and the mechanical properties of the lightweight stampable sheet deteriorate. If it exceeds 200,000, the impregnating property at the glass fiber joint is deteriorated and the mechanical properties of the sheet are deteriorated. Further, the fluidity is reduced. The amount of functional groups is 0.02-3.0
wt% [(weight of functional group / weight of matrix resin) x 1
00] is preferable. More preferably, it is 0.05 to 2.0 wt%. If it is less than 0.02 wt%, the adhesion with the silane coupling agent becomes insufficient and the improvement in strength becomes small. 3.0wt
If it exceeds%, the matrix resin becomes brittle and the sheet is colored.

The particles of the thermoplastic resin used in the web may be particles after polymerization, or particles obtained by so-called chemical crushing in which pelletized resin is mechanically crushed or once dissolved in a solvent and then precipitated. Good. The particles of the thermoplastic resin preferably have a diameter of 50 to 2000 μm. If the diameter is too large, it is difficult to obtain a consolidate sheet in which the resin is uniformly impregnated in the glass fiber. On the other hand, if the diameter is too small, pressure loss may increase in the dehydration step of producing a web, which will be described later, which may cause production troubles.

When the matrix resin and the modified resin are used in combination, a web may be produced by using the respective particles, or a product obtained by previously melt-kneading these with an extruder or the like and pulverizing them may be used. Also, a method of coating one resin with another resin can be used. <Consolidated sheet manufacturing method> Two types of reinforcing glass fiber chopped strands having different diameters and thermoplastic resin particles are uniformly dispersed in a surfactant aqueous solution in which air microbubbles are dispersed. A uniform web can be obtained by dehydrating this dispersion through the porous support. The web is composed of reinforcing glass fibers, a thermoplastic resin and the like, and particles of the thermoplastic resin are uniformly dispersed in the reinforcing glass fibers. The thickness of the web is about 1 to 10 mm. Next, after drying the web, the resin is melted by heating it to a temperature not lower than the melting point of the thermoplastic resin, and pressure is applied between cooling plates to obtain a dense solidified consolidate sheet.

The heating temperature when the web is heated and pressed to produce the consolidate sheet is from the melting point of the thermoplastic resin to the decomposition temperature. When the matrix resin is polypropylene, the heating temperature is preferably 170 to 230 ° C, more preferably 190 to 220 ° C. Above 230 ° C, discoloration of polypropylene and deterioration of strength occur. The pressure when pressing the web is preferably 3 to 500 kgf / cm ² for the purpose of obtaining a dense consolidate sheet. Excessive pressure can result in breakage of the reinforcing glass fibers.

The consolidate sheet may contain additives such as an antioxidant, a light resistance stabilizer, a metal deactivator, a flame retardant and carbon black, and a coloring agent. These additives and colorants can be contained in the consolidate sheet, for example, by preliminarily blending or coating with a granular thermoplastic resin or by adding them by spraying during the consolidate sheet manufacturing process.

<Expansion / Compression Molding Method> The consolidation sheet manufactured as described above is expanded / compression-molded by a known method to obtain a lightweight stampable sheet. That is, after heating the consolidate sheet above the melting point of the resin, it is placed on a molding die, the clearance of the die is adjusted, and expansion / compression molding is performed to obtain a lightweight stampable sheet having a predetermined thickness and density.

The heating temperature at the time of forming the consolidate sheet is not less than the melting point of the thermoplastic resin and not more than the decomposition temperature. When the thermoplastic resin is polypropylene, the heating temperature is preferably 170 to 230 ° C. More preferably, it is 190 to 210 ° C. The method for heating the consolidate sheet includes hot plate heating, infrared heating, and ventilation heating, and is not particularly limited. When heated, the consolidate sheet expands due to the springback of the reinforcing glass fiber. The expansion ratio is usually 1.1 to 7 times. If the expansion ratio is too large, the temperature difference between the surface temperature during heating and the central portion becomes large, and uniform heating becomes difficult, so it is preferable.
It is 1.3 to 6.5 times, more preferably 1.5 to 6 times.

The mold temperature may be below the freezing point of the thermoplastic resin. Usually room temperature ~ from the viewpoint of handling and productivity
60 ° C. The compression / molding pressure depends on the product shape,
Usually, it is 1 to 50 kgf / cm ² . Excessive pressure causes the reinforcing glass fibers to break. The density of the lightweight stampable sheet is controlled by the mold clearance. The theoretical density (ρ) when the porosity is zero can be obtained from the following equation.

Ρ = 100 / (W _m / ρ _m + W _f / ρ _f ) where W _m is the weight fraction of the matrix W _f is the weight fraction of the reinforcing glass fiber ρ _m is the density of the matrix ρ _f is the reinforcement It is the density of glass fiber for use.

The density of the lightweight stampable sheet may be smaller than the theoretical density. It is preferably 0.8 g / cm ³ or less, more preferably 0.7 g / cm ³ or less.

[0026]

EXAMPLES The present invention will be specifically described below based on examples. The matrix resin and the reinforcing glass fiber used in the examples are as follows. Matrix resin: polypropylene (weight average molecular weight 20
0000, average particle size 500 μm) Glass fiber chopped strand A: length 13 mm, diameter 10
μm, aminosilane 0.005 wt%, polyethylene oxide-based sizing agent 0.05 wt%, number of shunts 5000 / bundle Glass fiber chopped strand B: length 13 mm, diameter 23
μm, aminosilane 0.005 wt%, polyethylene oxide-based sizing agent 0.05 wt%, number of shunting fibers 5000 / bundle (Example 1) polypropylene 18.75 g, glass fiber chopped strand A (fiber diameter 10 μm) 8.12 g and glass fiber chopped strand B ( Fiber diameter 23 μm) 4.38 g was added to a sodium dodecylbenzenesulfonate 0.8 wt% aqueous solution.
The dispersion was prepared by stirring and foaming in 10 l. This dispersion is poured into a paper machine with a paper making area of 250 × 250 mm, suctioned and defoamed to produce a web with a basis weight of 500 g / m ²
Dried for hours. The web was preheated at 210 ℃, placed between the cooling boards at 25 ℃, pressed at a pressure of 5 kgf / cm ² , and solidified compact consolidate sheet (total glass fiber content 40 wt%, basis weight 500 g / m ² ) Obtained.

After heating the consolidate sheet with a far infrared heater until the surface temperature reaches 210 ° C., it is placed between flat plates at 20 ° C.,
After cooling naturally, the thickness of the expansion plate was measured. Next length is 150m
Bending test piece of m and width of 50 mm is cut out and the distance between spans is 100 m
A 3-point bending test was performed at m and a bending speed of 50 mm / min to measure the elastic gradient (kgf / cm). The results are shown in Table 1. Moreover, there was no tingling sensation when the surface of the expanded sheet was touched by hand.

(Examples 2 and 3), (Comparative Examples 1 to 4) A lightweight stampable sheet was prepared in the same manner as in Example 1 except that the mixing ratio of the glass fiber chopped strand A and the glass fiber chopped strand B was changed. Got The bending test of the expansion plate was performed, and the results are shown in Table 1.

[0029]

[Table 1]

Here, the mixing ratio of the reinforcing glass fiber [W2 / (W1 + W2)] =
The addition amount of the reinforcing glass fiber B / the addition amount of the reinforcing glass fiber A + the addition amount of the reinforcing glass fiber B), and each addition amount is a weight percentage of the reinforcing glass fiber in the consolidate sheet.

When the mixing ratio of the reinforcing glass fibers is small, there is no tingling sensation, but the rigidity is also small. When the mixing ratio is large, the rigidity is high, but the tingling sensation is severe and the handling is difficult. When the mixing ratio is 0.3 to 0.7, it is possible to obtain a well-balanced expansion plate that does not have a tingling sensation and has high rigidity.
In addition, the lightweight stampable sheet of the present invention hardly caused drawdown during molding.

[0032]

According to the present invention, it is possible to provide a lightweight stampable sheet having high strength and high toughness with improved expandability and handleability. This lightweight stampable sheet can be advantageously used for automobile interior members that require high strength and high toughness, such as ceiling materials and door trims.

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Claims (1)

[Claims] 1. A dispersion is prepared by dispersing a reinforcing glass fiber and a granular matrix resin in a surfactant-containing aqueous medium in which air microbubbles are dispersed, and the dispersion is formed on a porous support. Prepare a sheet-shaped web by
After drying, heat and pressure are applied to solidify the sheet, then heated above the melting point of the matrix resin and expanded in the thickness direction of the sheet, and the density is higher than the theoretical density when the porosity in the sheet is zero. In a light-weight stampable sheet produced by compression molding so that the fiber diameter becomes smaller, the reinforcing glass fiber is composed of two types of reinforcing glass fibers having different fiber diameters, and the addition amount of the small-diameter fiber is added to the stampable sheet. Is W1 wt% and the added amount of the large-diameter fiber is W2 wt%, and the value of W2 / (W1 + W2) is 0.3 to 0.7, which is a lightweight stampable sheet having excellent expandability and handleability.