JP2008255226A - Polyvinyl acetal resin composition and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition excellent in balance of transparency, tenacity, rigidity and surface hardness. <P>SOLUTION: Molded products are produced by melt-molding a resin composition comprising a polyvinyl acetal resin (A) and fumed silica (B), wherein, the resin composition contains 4-60 pts.wt. fumed silica (B) based on 100 pts.wt. polyvinyl acetal resin (A). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a transparent resin composition containing a polyvinyl acetal resin and fumed silica. Moreover, it is related with the manufacturing method of such a resin composition.

  Polyvinyl acetal resin is a material excellent in transparency and toughness, but on the other hand, it has been difficult to use it for a wide range of applications due to its remarkable lack of rigidity and surface hardness. Therefore, it has been required to provide a well-balanced transparent material with improved physical properties.

  As the transparent thermoplastic resin, a methacryl resin mainly composed of polymethyl methacrylate (PMMA), a polycarbonate (PC) resin, and the like are generally well known. However, the methacrylic resin mainly composed of PMMA is excellent in transparency, rigidity, and surface hardness, but has a drawback that the toughness is remarkably insufficient. Moreover, although PC is excellent in transparency and toughness, it has a drawback that rigidity and surface hardness are remarkably insufficient. As a method for improving the problems of these transparent materials, a composite of a transparent thermoplastic resin and an inorganic material has recently been studied.

  Patent Document 1 discloses a radiation curing method in which a silica particle dispersion is mixed with an organic solvent in which a dispersion stabilizing resin such as polyvinyl butyral (PVB) is dissolved, and a radiation curable monomer such as an acrylic monomer is further mixed. A resin composition is described. It is said that a laminate having high surface hardness can be obtained by applying this composition to a plastic layer and curing it.

  Patent Document 2 describes functional glazing in which an inorganic glass matrix such as silica formed by a sol-gel method is impregnated with a liquid resin and then solidified.

  Patent Document 3 describes a plastic lens in which a primer layer made of a crosslinked polyvinyl acetal resin is provided on the surface of a plastic lens substrate, and then a hard coat layer is provided thereon. At this time, as the primer layer, an acidic solution containing a polyvinyl acetal resin and a hydrolyzable organosilane compound can be used, and it is described that the primer layer is crosslinked by a hydrolyzate or condensate of an organosilane compound. Thereby, it is said that a plastic lens excellent in impact resistance can be obtained.

  Non-Patent Document 1 discloses that a polyvinyl butyral (PVB), alkoxysilane and colloidal silica are reacted in 2-propanol and coated on a transparent polyurethane substrate to prepare a PVB-silica composite thin film sample. Are listed. Thereby, it is said that the transparent uniform thin film with favorable adhesiveness and high hardness is obtained.

  Non-Patent Document 2 discloses that a PMMA-silica hybrid material is obtained by a sol-gel method by mixing a tetrahydrofuran (THF) solution of polymethyl methacrylate (PMMA) with a water / ethanol solution containing tetraethoxysilane and hydrochloric acid. Is described to create. It has been shown that the silanol group and the carbonyl group form hydrogen bonds at the interface between the organic phase and the inorganic phase, so that both phases can be highly mixed.

  Patent Document 4 discloses a method for producing a nanocomposite resin composition, in which colloidal silica is dried to a powder, and then dispersed in a monomer such as methyl methacrylate (MMA), followed by a polymerization reaction to form a composite. Is described. A silica-containing resin composition having improved rigidity, surface hardness, and thermal stability is obtained by dispersing silica in the PMMA matrix on the nano order.

  However, when the substrate is PET or PMMA, the toughness is insufficient and it is difficult to say that the transparent material is balanced. In addition, the method of producing inorganic fine particles by the sol-gel method does not improve toughness, and the production cost is high, which is not practical. Furthermore, mixing the thermoplastic resin and the inorganic fine particles in a solution state using a solvent is not practical in the manufacturing process and is expensive. In addition, when a laminated structure is adopted, the process is complicated and there is a risk of peeling, which is a problem.

JP-A-2-273233 JP-A-7-172881 JP-A-7-306302 Japanese Patent Laid-Open No. 2004-161895 Hiroki Yuki, “Preparation of Polyvinyl Butyral-Silica Composite Thin Film and Its Impact Resistance”, Aichi Prefectural Institute of Industrial Technology Research Report, 2003 C. -K. Chan and three others, Polymer, 2001, Vol. 42, p. 4189-4196

  An object of the present invention is to provide a resin composition excellent in transparency, toughness, rigidity, and surface hardness. Moreover, it is providing the manufacturing method which can manufacture such a resin composition easily at low cost.

  The said subject is a resin composition containing polyvinyl acetal resin (A) and fumed silica (B), Comprising: 4-60 weight part of fumed silica (B) with respect to 100 weight part of polyvinyl acetal resin (A) It is solved by providing the resin composition characterized by containing this. Here, the polyvinyl acetal resin (A) is preferably obtained by acetalizing polyvinyl alcohol having an average polymerization degree of 200 to 4000. Moreover, it is preferable that the acetalization degree of polyvinyl acetal resin (A) is 55-83 mol%. Furthermore, it is also preferable that the polyvinyl acetal resin (A) is a polyvinyl butyral resin.

  When the resin composition is molded to a thickness of 1 mm, it is preferable that the visible light transmittance is 80% or more and the haze value is 10% or less. In addition, when molded into a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm, the bending elastic modulus calculated from the bending stress at a strain of 1% is 2000 MPa or more and the strain until the test piece breaks. Is preferably 10% or more. Furthermore, when molded into a No. 2 type test piece (thickness 1 mm) described in JIS K7113, the tensile modulus calculated from the tensile stress at 1% strain is 2000 MPa or more, and the test piece is broken until it breaks. It is also preferable that the elongation is 10% or more. It is also preferable that the amount of change in the glass transition temperature is 3 ° C. or less compared to a resin composition having the same composition except that fumed silica (B) is not added.

  A molded article comprising the above resin composition is a preferred embodiment of the present invention. At this time, the pencil hardness of the molded product is preferably F or more. Moreover, the film which consists of said resin composition is also a suitable embodiment of this invention.

The said subject is also solved by providing the manufacturing method of the said resin composition by melt-kneading polyvinyl acetal resin (A) and fumed silica (B). At this time, it is preferable that the fumed silica (B) is added to the melted polyvinyl acetal resin (A) and melt-kneaded. It is also preferable to perform melt-kneading under conditions where the molten resin temperature is 140 ° C. or higher, the melt viscosity is 10,000 Pa · s or lower, and the maximum shear rate is 100 sec ⁻¹ or higher.

  The resin composition of the present invention is excellent in transparency, toughness, rigidity, and surface hardness when molded into a sheet or the like, and can provide a molded product that can be easily manufactured at low cost in the manufacturing process and cost.

  The present invention is described in detail below. This invention is a resin composition containing polyvinyl acetal resin (A) and fumed silica (B), Comprising: 4-60 weight part of fumed silica (B) with respect to 100 weight part of polyvinyl acetal resin (A) It is a resin composition characterized by containing. By adopting such a configuration, a molded product having an excellent balance of transparency, toughness, rigidity, and surface hardness can be obtained.

  The polyvinyl acetal resin (A) used in the present invention was reacted by reacting polyvinyl alcohol (PVA) with an aldehyde in water and / or an organic solvent in the presence of an acid catalyst, and neutralized and washed as necessary. Thereafter, it can be obtained by drying. The structure of the obtained polyvinyl acetal resin (A) is as shown in the following formula (I).

  In the above formula (I), k + 1 + m = 1. R represents the residue of the aldehyde used in the acetalization reaction. At this time, different aldehydes may be used in combination. In the above formula, the arrangement method of each bond is not particularly limited, and may be block-like or random.

The degree of acetalization of the polyvinyl acetal resin (A) is preferably 55 to 83 mol%. A polyvinyl acetal resin having an acetalization degree of less than 55 mol% is not preferable because the production process becomes complicated, the production cost increases, and the melt processability also decreases. On the other hand, if it is attempted to acetalize PVA exceeding 83 mol%, it is necessary to lengthen the acetalization reaction time, which is economically disadvantageous. As the polyvinyl acetal resin (A), one type may be used alone, or two or more types may be mixed and used. Here, the degree of acetalization (mol%) is represented by the following formula, and according to the formula (I), it is expressed as [2k / (2k + 1 + m)] × 100 (mol%). It is.
Degree of acetalization (mol%) = [(number of moles of acetalized hydroxyl groups) / (total number of moles of hydroxyl groups and acetyl groups in raw polyvinyl alcohol)] × 100

  The PVA used for the production of the polyvinyl acetal resin (A) is not particularly limited, and a conventionally known PVA such as one produced by saponifying polyvinyl acetate or the like using an alkali catalyst or an acid catalyst may be used. it can. The PVA may be fully saponified or partially saponified. The saponification degree is preferably 80 mol% or more, more preferably 90 mol% or more, and further preferably 95 mol% or more. One type of PVA may be used alone, or two or more types may be mixed and used. As PVA, a copolymer with a monomer copolymerizable with vinyl alcohol, such as an ethylene-vinyl alcohol copolymer or a partially saponified ethylene-vinyl alcohol copolymer, can also be used. Furthermore, modified PVA into which a functional group such as carboxylic acid is partially introduced can also be used.

  Moreover, it is preferable that the average degree of polymerization of PVA used for manufacture of polyvinyl acetal resin (A) is 200-4000. More preferably, it is 200-3000, More preferably, it is 300-2000. When the average degree of polymerization of PVA is 200 or less, the mechanical properties of the obtained molded article are lowered. On the other hand, when the average degree of polymerization of the polyvinyl acetal resin exceeds 4000, the melt viscosity at the time of melt-kneading the obtained resin composition becomes too high, and the production becomes difficult. The average degree of polymerization is calculated by calculating the relative viscosity after saponifying the non-saponified portion (vinyl acetate group) with sodium hydroxide in advance and then determining the relative viscosity with water using a viscometer. (JIS K6726).

  The aldehyde used for the production of the polyvinyl acetal resin (A) is not particularly limited. For example, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde , 2-ethylhexylaldehyde, cyclohexylaldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropion Examples include aldehydes. These aldehydes may be used alone or in combination of two or more. As the aldehyde, butyraldehyde is particularly preferably used from the viewpoints of industrial availability and ease of production. That is, the polyvinyl acetal resin (A) is particularly preferably polyvinyl butyral. At this time, butyraldehyde may be mainly used and another aldehyde may be used in combination.

  The acetalization reaction, neutralization, dehydration, and washing of PVA are not particularly limited and can be performed by a known method. For example, an aqueous medium method in which an aqueous solution of PVA and an aldehyde are acetalized in the presence of an acid catalyst to precipitate resin particles, PVA is dispersed in an organic solvent, and an acetalization reaction is performed with an aldehyde in the presence of an acid catalyst. The solvent method etc. which precipitate a liquid on the water etc. which are poor solvents with respect to polyvinyl acetal resin are applicable. Whichever method is used, a slurry in which the polyvinyl acetal resin is dispersed in the medium is obtained.

  Since the slurry obtained by these methods is acidic by an acid catalyst, an alkaline neutralizing agent such as sodium hydroxide or sodium carbonate is added as necessary, and the pH is 5 to 9, preferably Is adjusted to be 6 to 9, more preferably 6 to 8. Next, dehydration and washing are performed, followed by drying to obtain a polyvinyl acetal resin in the form of powder, granules or pellets.

  The acid catalyst used is not particularly limited, and examples thereof include organic acids such as acetic acid and p-toluenesulfonic acid, and inorganic acids such as nitric acid, sulfuric acid, and hydrochloric acid. Further, the neutralizing agent after the acetalization reaction is not particularly limited, but examples thereof include alkalis such as sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and alkylenes such as ethylene oxide. Examples thereof include glycidyl ethers such as oxides and ethylene glycol diglycidyl ether.

The fumed silica (B) used in the present invention is preferably produced by a dry method. Examples of fumed silica include AEROSIL from Degussa, REOLOSIL from Tokuyama, CAB-O-SIL from Cabot, and the like. Fumed silica can be obtained by high-temperature hydrolysis of highly purified silicon tetrachloride in an oxyhydrogen flame. The fumed silica (B) needs to be finely dispersed in the resin composition. When the fumed silica (B) is not finely dispersed, light is scattered under visible light, and haze is deteriorated. In general, it is desirable to finely disperse so as to have a particle size of about ¼ or less of the wavelength of light. Therefore, the average primary particle size of fumed silica (B) is preferably 50 nm or less, More preferably, it is 20 nm or less. Moreover, it is preferable that an average primary particle diameter is 5 nm or more, and it is more preferable that it is 7 nm or more. If the average primary particle diameter is smaller than 5 nm, the cohesive force between the silica particles becomes too strong as the surface area increases, and it may be difficult to finely disperse. It is preferable that the specific surface area of fumed silica (B) is 50-500 m < ² > / g by BET method. The specific surface area is more preferably 100 m ² / g or more, and more preferably 300 m ² / g or less.

  The compounding ratio of the polyvinyl acetal resin (A) and the fumed silica (B) is 4 to 60 parts by weight of the fumed silica (B) with respect to 100 parts by weight of the polyvinyl acetal resin (A). By including the blended amount of fumed silica (A) within this range, a molded product having an excellent balance of rigidity, surface hardness and toughness can be obtained. Here, it is important that the blended amount of fumed silica (A) is 4 parts by weight or more, whereby a molded product having sufficient rigidity and surface hardness can be obtained. In other words, sufficient rigidity and surface hardness improvement effect can be obtained for the first time by blending in a large amount to some extent. The amount of fumed silica (A) is preferably 6 parts by weight or more, and more preferably 10 parts by weight or more. On the other hand, when the compounding quantity of fumed silica (A) exceeds 60 weight part, toughness will fall and the toughness which polyvinyl acetal resin (A) originally had will be impaired greatly. The amount of fumed silica (A) is preferably 40 parts by weight or less, and more preferably 30 parts by weight or less.

  The resin composition of the present invention is preferably produced by melt-kneading a polyvinyl acetal resin (A) and fumed silica (B). The form of the polyvinyl acetal resin (A) used is not particularly limited, and for example, a powder form, a pellet form, a fiber form, a strand form, or a film form can be used. Further, fumed silica (B) is preferably used in a powder form. When powdered fumed silica (B) is used, it is not necessary to remove the dispersion medium, compared to the case of using silica sol. Can be reduced. The polyvinyl acetal resin (A) and the fumed silica (B) may be mixed in advance and then introduced into the kneading apparatus, but the fumed silica (B) is added to the molten polyvinyl acetal resin (A). It is preferable to melt and knead. By doing so, a resin composition in which silica fine particles are more uniformly dispersed is obtained.

  The apparatus used when melt-kneading the polyvinyl acetal resin (A) and the fumed silica (B) is not particularly limited as long as both can be uniformly kneaded. Especially, the kneading apparatus which can provide strong shearing force like a roller mixer and a twin-screw extruder is used suitably. By giving a strong shearing force, aggregation of particles can be broken and silica particles can be highly dispersed in the resin.

There are no particular restrictions on the melting conditions for producing the resin composition by the melt-kneading method, but it is preferably carried out under the following conditions. The molten resin temperature at the time of kneading is preferably 140 ° C. or higher, and more preferably 180 ° C. or higher in order to obtain good plasticity. The molten resin temperature is preferably 300 ° C. or lower and more preferably 250 ° C. or lower in order to prevent thermal decomposition and prevent the melt viscosity from becoming too low and the shearing force to decrease. Further, the melt viscosity at the molten resin temperature is preferably 10,000 Pa · s or less, and more preferably 8000 Pa · s or less, for easy mixing with a normal kneading apparatus. On the other hand, if the melt viscosity is too low, the shearing force may be reduced during kneading, so that it is preferably 50 Pa · s or more, and more preferably 100 Pa · s or more. Further, preferably the maximum shear rate is 100 sec ^-1 or more, and more preferably 200 sec ^-1 or more. On the other hand, in order to mix easily with a normal kneading apparatus, the maximum shear rate is preferably 5000 sec ⁻¹ or less. By adopting the above conditions, a resin composition in which silica particles are highly dispersed can be obtained.

  In the resin composition of the present invention, various additives such as an antioxidant, a stabilizer, an ultraviolet absorber, a lubricant, a flame retardant, a processing aid, and an antistatic agent are added as necessary as long as the effects of the invention are not impaired. An agent, a colorant, an impact resistance aid, an adhesive strength modifier, a filler, a moisture resistance agent and the like may be added. In addition, in order to obtain the molded article excellent in rigidity, it is preferable that a plasticizer is not included substantially.

  The resin composition thus obtained preferably has a visible light transmittance of 80% or more when molded to a thickness of 1 mm. When the visible light transmittance is 80% or more, it can be widely used as a transparent material. The visible light transmittance is more preferably 85% or more. Moreover, when it shape | molds in thickness 1mm, it is preferable that a haze value is 10% or less. When the haze value is 10% or less, it can be widely used as a transparent material. The haze value is more preferably 5% or less.

  When the resin composition of the present invention is molded into a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm, the flexural modulus calculated from the bending stress at 1% strain is 2000 MPa or more, and the test piece It is preferable that the strain until the rupture is 10% or more. When the flexural modulus is 2000 MPa or more, sufficient rigidity can be exhibited when used as a molded product. The flexural modulus is more preferably 2200 MPa or more. When the strain until the test piece breaks is 10% or more, sufficient toughness can be exhibited when used as a molded product. The breaking strain is more preferably 20% or more, and even more preferably 30% or more.

  Moreover, when the resin composition of the present invention is molded into a No. 2 type test piece (thickness 1 mm) described in JIS K7113, the tensile elastic modulus calculated from the tensile stress at 1% strain is 2000 MPa or more, And it is preferable that elongation until a test piece fractures is 10% or more. When the tensile elastic modulus is 2000 MPa or more, sufficient rigidity can be exhibited when used as a molded product. The tensile elastic modulus is more preferably 2200 MPa or more. When the elongation until the test piece breaks is 10% or more, sufficient toughness can be exhibited when used as a molded product. The breaking elongation is more preferably 20% or more, and even more preferably 30% or more.

  Moreover, it is preferable that the variation | change_quantity of a glass transition temperature is 3 degrees C or less compared with the resin composition of the same composition except the fumed silica (B). The amount of change in the glass transition temperature is more preferably within 2 ° C.

  A molded article is obtained by molding the resin composition of the present invention. The molding method is not particularly limited, but melt molding is preferred. As the melt molding, various molding methods such as extrusion molding and injection molding can be employed. Moreover, it can also be set as a laminated body with another raw material. The polyvinyl acetal resin (A) and fumed silica (B) may be melt-kneaded in an extruder and molded as it is.

  The molded article of the present invention preferably has a surface pencil hardness of F or higher. When the pencil hardness is F or more, the occurrence of scratches due to friction on the surface can be suppressed. This is important because transparent molded articles generally dislike that the surface is scratched and the transparency is impaired. The pencil hardness is more preferably H or higher.

  Since the molded article of the present invention is excellent in transparency, toughness, rigidity and surface hardness, it is used as various molded articles requiring transparency and mechanical properties, for example, films, sheets or injection molded articles. Because of demands on transparency and mechanical properties, it can be suitably used in applications where acrylic resins, polycarbonate resins, and the like are currently used. For example, wall materials such as sound insulation walls such as highways, building materials such as window materials, optical members such as optical lenses and video lenses, members for vehicles, members for home appliances, food packaging trays and lids, cups, etc. It can use suitably for the use of.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by this Example. In the following examples, visible light transmittance, haze, flexural modulus, strain, tensile modulus, elongation, surface hardness, glass transition temperature, silica particle diameter, silica specific surface area and melt viscosity are as follows. It was measured.

[Visible light transmittance]
Using a spectrophotometer UV-4100 manufactured by Hitachi, Ltd., the transmittance in a wavelength region of 280 to 2500 nm was measured for a test piece having a thickness of 1 mm, and the visible light transmittance up to 380 to 780 nm was measured according to JIS R 3106. Asked.

[Haze]
According to JIS K7105, the haze of a test piece having a thickness of 1 mm was determined.

[Flexural modulus and strain]
Evaluation of rigidity (elastic modulus) and toughness (breaking strain) in a bending test was carried out using a test piece of length 80 mm × width 10 mm × thickness 4 mm using an autograph AG-5000B manufactured by Shimadzu Corporation according to JIS K7171. And measured at a strain rate of 1 mm / min. The rigidity was evaluated by a flexural modulus (MPa) calculated from a bending stress at a strain of 1% from the start of the test. The toughness was evaluated by the strain (%) until the test piece broke.

[Tensile modulus and elongation]
Evaluation of rigidity (elastic modulus) and toughness (elongation at break) in a tensile test was carried out according to JIS K7162, using an autograph AG-5000B manufactured by Shimadzu Corporation. (Thickness 1 mm) was used and measured at a tensile speed of 5 mm / min. The rigidity was evaluated by a tensile elastic modulus (MPa) calculated from a tensile stress at a tensile strain of 1%. Toughness was evaluated by elongation (%) until the test piece broke.

[surface hardness]
The surface hardness was measured in accordance with JIS K5400, and the pencil hardness of a test piece having a thickness of 1 mm was measured.

[Glass-transition temperature]
Evaluation of the glass transition temperature was performed using a test piece having a length of 20 mm, a width of 3 mm, and a thickness of 1 mm, using a rheology FT Rheospectrer DVE-V4 with a sine frequency of 10 Hz and a temperature rising rate of 3 ° C./min Under the conditions, the peak temperature (Tg) of the loss tangent (tan δ) of the main dispersion was determined. Both the glass transition temperature (Tgb) after addition of fumed silica and the glass transition temperature (Tga) of the polyvinyl acetal resin before addition were determined.

[Silica particle size]
The particle diameter of silica was determined using an H-800NA transmission electron microscope (TEM). Arbitrary 500 silica particles were selected from the photograph of the cross section of the film, their sizes were measured, and the average primary particle size was obtained.

[Specific surface area of silica]
In accordance with DIN 66131, the specific surface area of the silica used was measured by the BET method.

[Melt viscosity]
The melt viscosity was measured using CAPIROGRAPH 1D manufactured by Toyo Seiki Seisakusho. The specifications of the apparatus are a barrel diameter of 9.55 mmφ, a capillary length (L) of 10 mm, a capillary diameter (D) of 1 mm, L / D = 10, and a barrel material SACM (nitrified steel).

[Method for producing polyvinyl acetal resin]
PVA (275 g) having a polymerization degree of 800 and a saponification degree of 99 mol% was dissolved in pure water (2890 g) while heating, and the temperature was adjusted to 12 ° C., and 35 wt% hydrochloric acid (201 g) and n-butyraldehyde ( 148 g) was added and the temperature was maintained for 2 hours to precipitate the reaction product. Thereafter, the reaction system is maintained at 45 ° C. for 3 hours to complete the reaction, washed with excess water, unreacted aldehyde is washed away, the remaining hydrochloric acid is neutralized with an aqueous sodium hydroxide solution, and dehydrated. The polyvinyl acetal resin (A-1) was obtained by washing again with a large excess of water until pH = 7 and drying until the volatile content was 1.0%. Polyvinyl acetal resins (A-2 to 4) were obtained by changing the PVA and aldehyde compounds used as described in Table 1.

[silica]
As shown in Table 2, the total of two types of fumed silica AEROSIL (manufactured by Degussa) manufactured by a dry method, REOLOSIL (manufactured by Tokuyama Corporation), and NIPGEL (manufactured by Tosoh Silica Co., Ltd.) manufactured by a wet method Four types of silica were used.

Example 1
Silica B-1 (5 weight) in a state where polyvinyl acetal A-1 (100 parts by weight) was melted at a resin temperature of 200 ° C. and a rotation speed of 100 rpm using a roller mixer R60 type lab plast mill manufactured by Toyo Seiki Co., Ltd. Part) was added to obtain a resin composition. The obtained resin composition was hot-pressed at 140 ° C. for 5 minutes to prepare test pieces each having a length of 200 mm × width of 200 mm × thickness of 1 mm and length of 80 mm × width of 10 mm × thickness of 4 mm. The melt viscosity at 200 ° C. of the obtained resin composition was 200 Pa · s. Moreover, the maximum shear rate at the time of melt-kneading was 250 sec- ¹ . Using these test pieces, visible light transmittance, haze, flexural modulus, strain, tensile modulus, elongation, pencil hardness, and glass transition temperature (Tgb) were measured. The results are shown in Table 3.

Examples 2-8
A test piece was prepared from the resin composition in the same manner as in Example 1 except that the type and weight of polyvinyl acetal to be used and the type and weight of silica were changed as shown in Table 3, and physical properties were evaluated. The results are shown in Table 3.

Comparative Examples 1-6
The resin composition was used in the same manner as in Example 1 except that the type and weight of polyvinyl acetal used were changed as shown in Table 4 and silica was not used or the type and weight were changed as shown in Table 4. Test pieces were prepared and evaluated for physical properties. The results are shown in Table 4.

Comparative Example 7
100 g of PMMA (PARAPET G manufactured by Kuraray Co., Ltd.), which is generally used as a transparent material, is melted at a resin temperature of 220 ° C. and a rotation speed of 100 rpm using a lab plast mill, and the resulting resin composition is 220 ° C. A heat press was performed for 5 minutes, a test piece was prepared in the same manner as in Example 1, and physical properties were evaluated. The results are shown in Table 4.

Comparative Example 8
Resin obtained by melting at a resin temperature of 260 ° C. and a rotation speed of 100 rpm using a lab plast mill using 100 g of PC (Teijin Corporation Panlite L-1225) that is generally used as a transparent material The composition was hot-pressed at 250 ° C. for 5 minutes, test pieces were prepared in the same manner as in Example 1, and physical properties were evaluated. The results are shown in Table 4.

  From the results shown in Table 3 and Table 4, the resin composition of the present invention has transparency (visible light transmittance, haze), rigidity (bending / tensile modulus), toughness (breaking strain, breaking elongation), surface hardness (pencil) It can be seen that this is a well-balanced transparent material with excellent hardness. Also, when fumed silica is not used or when the amount used is small, transparency and rigidity are not sufficient, and transparent materials such as PMMA and PC are not sufficient in rigidity, toughness and surface hardness, and may lack balance. Recognize.

Claims (14)

  It is a resin composition containing polyvinyl acetal resin (A) and fumed silica (B), and contains 4 to 60 parts by weight of fumed silica (B) with respect to 100 parts by weight of polyvinyl acetal resin (A). A resin composition characterized by the above.   The resin composition according to claim 1, wherein the polyvinyl acetal resin (A) is obtained by acetalizing polyvinyl alcohol having an average degree of polymerization of 200 to 4000.   The resin composition according to claim 1 or 2, wherein the degree of acetalization of the polyvinyl acetal resin (A) is 55 to 83 mol%.   The resin composition according to any one of claims 1 to 3, wherein the polyvinyl acetal resin (A) is a polyvinyl butyral resin.   The resin composition according to any one of claims 1 to 4, which has a visible light transmittance of 80% or more and a haze value of 10% or less when molded into a thickness of 1 mm.   When molded into a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm, the flexural modulus calculated from the bending stress at 1% strain is 2000 MPa or more, and the strain until the test piece breaks is 10 % Or more of the resin composition according to claim 1.   When molded into a No. 2 type test piece (thickness 1 mm) described in JIS K7113, the tensile modulus calculated from the tensile stress at 1% strain is 2000 MPa or more, and the elongation until the test piece breaks It is 10% or more, The resin composition in any one of Claims 1-6.   The resin composition according to any one of claims 1 to 7, wherein the amount of change in the glass transition temperature is 3 ° C or less as compared with a resin composition having the same composition except that fumed silica (B) is not added.   A molded article comprising the resin composition according to claim 1.   The molded article according to claim 9, wherein the pencil hardness is F or more.   The film which consists of a resin composition in any one of Claims 1-8.   The method for producing a resin composition according to any one of claims 1 to 8, wherein the polyvinyl acetal resin (A) and the fumed silica (B) are melt-kneaded.   The method for producing a resin composition according to claim 12, wherein fumed silica (B) is added to the melted polyvinyl acetal resin (A) and melt kneaded. The method for producing a resin composition according to claim 12 or 13, wherein the molten resin temperature is 140 ° C or higher, the melt viscosity is 10,000 Pa · s or lower, and the maximum shear rate is 100 sec ^-1 or higher.