JP2018083926A - Production method of resin moldings - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of resin moldings having excellent elastic modulus and flexure strength while maintaining optical properties such as whiteness and opacity as high as possible.SOLUTION: A production method of resin moldings of the present invention includes: a step of obtaining a resin composition by mixing a first thermoplastic resin, a second thermoplastic resin having a melting point higher than that of the first thermoplastic resin, and inorganic powder; a step of extending the resin composition at a temperature lower than the melting point of the first thermoplastic resin; and a step of heating the extended resin composition at a temperature higher and equal to the melting point of the first thermoplastic resin and lower than the melting point of the second thermoplastic resin.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a resin molded body.

  When manufacturing a resin molding by blending inorganic fine powder with a thermoplastic resin, it is important to balance optical properties such as whiteness and opacity and mechanical properties such as elastic modulus and bending strength. .

  In order to obtain a sheet of a resin molded body with a high blend of inorganic fine powder, a method has been proposed in which a sheet is prepared by highly blending an inorganic fine powder with a resin and the sheet is further stretched. That is, in Patent Document 1, a resin composition containing 60% to 82% by weight of an inorganic substance powder and 18% to 40% by weight of a thermoplastic resin is kneaded and formed into a sheet shape through a die, and then longitudinally and / or A manufacturing method of a thin film sheet with high blending of inorganic substance powder, which is stretched in the transverse direction to improve whiteness and opacity, is disclosed.

JP 2013-10931 A

  A plastic sheet mainly composed of a thermoplastic resin is generally transparent or nearly transparent. When this sheet is filled with inorganic fine powder, the opacity of the sheet is improved, but the whiteness remains at a low level.

  Even in the above case, when the stretch ratio is increased, the whiteness is remarkably improved and the opacity is slightly improved, but the bending strength is lowered. However, after that, practical problems started to appear, particularly in bending strength of the stretched sheet.

  On the other hand, when a resin molded body sheet containing a thermoplastic resin as a main component is stretched, a heat treatment (so-called annealing treatment) is usually performed after the stretching at a glass transition point, a softening point, or a softening point of the raw thermoplastic resin. There are many. The purpose is to prevent dimensional changes and strength reductions that occur after a product is produced due to the residual stress in the sheet generated up to the previous process.

  However, as the heat treatment referred to as the annealing treatment, there are usually many methods for maintaining a high temperature for a long time or longer.

  The present invention has been made in view of the above circumstances, and provides a method for producing a resin molded article excellent in elastic modulus and bending strength while keeping optical properties such as whiteness and opacity as high as possible. For the purpose.

  The inventors first conducted an experiment to determine how the balance between the optical properties of the whiteness and opacity of the sheet and the bending strength changed by stretching. The results shown in Table 1 below were obtained. That is, when the inorganic fine powder is filled and the stretching is strengthened, the whiteness is remarkably improved, the opacity is slightly increased, and some of the measured values reach 100%. However, the bending strength was remarkably reduced, and a tendency to decrease the tensile strength was recognized.

  In order to improve the above-mentioned problems, the present inventors performed a heat treatment temperature after stretching at a temperature higher than one melting point and lower than the other melting point for two types of thermoplastic resins having different melting points. In addition, the inventors have found that it is possible to obtain a resin molded article excellent in elastic modulus and bending strength while maintaining opacity as high as possible, and have completed the present invention. More specifically, the present invention aims to provide the following.

(1) A method for producing a resin molded body,
Mixing a first thermoplastic resin, a second thermoplastic resin having a higher melting point than the first thermoplastic resin, and an inorganic fine powder to obtain a resin composition;
Stretching the resin composition below the melting point of the first thermoplastic resin;
Heat-treating the stretched resin composition at a temperature not lower than the melting point of the first thermoplastic resin and lower than the melting point of the second thermoplastic resin.

  (2) The method according to (1), wherein in the step of obtaining the resin composition, the inorganic fine powder is mixed by 50% by mass or more based on the mass of the entire resin composition.

  (3) The method according to (1) or (2), wherein the first thermoplastic resin is polyethylene and the second thermoplastic resin is polypropylene.

  (4) The method according to any one of (1) to (3), wherein the inorganic fine powder includes calcium carbonate.

  ADVANTAGE OF THE INVENTION According to this invention, the resin molding excellent in the balance of whiteness and opacity, bending strength, and an elasticity modulus can be obtained.

  Hereinafter, although embodiment of this invention is described in detail, this invention is not limited to the following embodiment at all. Modifications can be made as appropriate within the scope of the object of the present invention.

  In the method for producing a resin molded body of the present invention, a first thermoplastic resin, a second thermoplastic resin having a melting point higher than that of the first thermoplastic resin, and an inorganic fine powder are mixed to obtain a resin composition. A step of stretching the resin composition below the melting point of the first thermoplastic resin, and a stretching of the resin composition at or above the melting point of the first thermoplastic resin and less than the melting point of the second resin. And a step of heat-treating at a temperature.

  The present invention includes a step of stretching the resin composition containing the first thermoplastic resin, the second thermoplastic resin, and the inorganic fine powder at a temperature lower than the melting point of the first thermoplastic resin. In addition, a large number of pores are formed in the resin composition. Furthermore, in the subsequent step, the elastic modulus and the bending strength are improved by heat-treating the resin composition at a temperature not lower than the melting point of the first thermoplastic resin and lower than the melting point of the second resin, While the internal strain is removed, many of the pores derived from the first thermoplastic resin are blocked, and many of the pores derived from the second thermoplastic resin remain, so the whiteness and opacity are relatively high. Maintained. As a result, it is possible to obtain a resin molded article having an excellent balance between optical properties such as whiteness and opacity, and mechanical properties such as elastic modulus and bending strength.

  Hereafter, each process in the manufacturing method of the resin molding of this invention is each demonstrated.

[Step of obtaining resin composition]
In the step of obtaining the resin composition in the present invention, the first thermoplastic resin, the second thermoplastic resin, and the inorganic fine powder are mixed to obtain a resin composition. Specifically, the first thermoplastic resin, the second thermoplastic resin, and the inorganic fine powder are melted and kneaded at a temperature equal to or higher than the melting point of the second thermoplastic resin to obtain a resin composition. The resin composition can be obtained by kneading in advance with a kneading machine, once producing mixed pellets, then forming into a sheet with an extrusion molding machine, or directly kneading by biaxial extrusion molding or the like. The molding may be performed with a single machine to form a sheet. From the viewpoint of uniformly dispersing the inorganic fine powder in the thermoplastic resin, it is preferable to knead by applying a high shear stress, for example, kneading with a biaxial kneader. Moreover, since the resin composition containing an inorganic fine powder has a high viscosity at the time of melting, the design is such that the kneading part of the extruder is lengthened.

[Step of stretching resin composition]
In the step of stretching the resin composition in the present invention, the resin composition is stretched at a temperature lower than the melting point of the first thermoplastic resin. By stretching the resin composition below the melting point of the first thermoplastic resin, pores are likely to be generated in the resin composition, and a resin molded product having high opacity and whiteness can be easily obtained.

  The stretching conditions need to be set as appropriate according to the desired specific gravity (density) according to the resin molded body, and are uniaxial in the longitudinal or lateral direction, or sequentially or simultaneously biaxially stretched in the longitudinal and lateral directions. Adopt one of the following.

The necessary draw ratio can also be calculated by calculation. The weight per square meter (also referred to as basis weight) W (g / m ² ) of the resin composition before being stretched is measured, and the apparent specific gravity D and aspect ratio (longitudinal direction and vertical direction) of the product determined in the production plan are measured. Using the following formula to determine the draw ratio (X times in the longitudinal direction and Y times in the transverse direction) using the ratio R of the draw ratio in the transverse direction (R) and the target value T (cm) of the thickness of the product after transverse stretching In addition, it can be easily estimated by operating experience for each device.
(Formula 1)
X ² = W × 10 ⁻⁴ / (D × Z × R × T)
X = RY
Where D: Apparent specific gravity of the product as defined in the production plan
R: Aspect ratio determined by production plan (ratio of stretching ratio in the longitudinal direction and the transverse direction)
W: Weight per square meter of thin film material before applying longitudinal stretching (g)
X: Longitudinal stretch ratio
Y: Stretch ratio in the transverse direction
Z: Shrinkage ratio or expansion ratio of the length in the transverse direction of the sheet by longitudinal stretching

[Step of heat treatment]
In the heat-treating step in the present invention, the stretched resin composition is heat-treated at a temperature not lower than the melting point of the first thermoplastic resin and lower than the melting point of the second thermoplastic resin. As a result, the heat-treated resin molded body is freed from internal strain, and at least a part of the pores derived from the first thermoplastic resin is blocked, leaving the pores derived from the second thermoplastic resin. . As a result, it is possible to obtain a resin molded article having excellent bending strength and elastic modulus while maintaining whiteness and opacity at a considerable level.

  By changing the heat treatment process conditions, particularly the heat treatment temperature, the whiteness and opacity values vary greatly. When the stretched resin composition is heat-treated at a temperature lower than the melting point of the first thermoplastic resin, even if opacity and whiteness are ensured, bending strength and elastic modulus are lowered. When the stretched resin composition is heat-treated at a temperature above the melting point of the second thermosetting resin, the opacity and whiteness are lowered even if the bending strength and the elastic modulus are ensured.

  The temperature for the heat treatment is not particularly limited as long as the temperature is equal to or higher than the melting point of the first thermoplastic resin and lower than the melting point of the second thermoplastic resin, and may be appropriately set according to the melting points of both. From the viewpoint of securing the bending strength and the elastic modulus, the melting point of the second thermoplastic resin is preferably closer to the melting point of the second thermoplastic resin than the melting point of the first thermoplastic resin. It is preferably the melting point of the second thermoplastic resin, more preferably the melting point of the second thermoplastic resin −30 ° C. to the melting point of the second thermoplastic resin, and the melting point of the second thermoplastic resin. It is more preferable that the melting point is −20 ° C. to the melting point of the second thermoplastic resin, and it is even more preferable that the melting point is −10 ° C. to the melting point of the second thermoplastic resin. On the other hand, from the viewpoint of increasing whiteness and opacity, the heat treatment temperature is preferably closer to the melting point of the first thermoplastic resin than the melting point of the second thermoplastic resin, for example, the first thermoplastic resin. The melting point of the first thermoplastic resin is more preferably + 40 ° C., the melting point of the first thermoplastic resin to the melting point of the first thermoplastic resin + 30 ° C. is more preferable, and the first heat The melting point of the plastic resin to the melting point of the first thermoplastic resin + 20 ° C. is even more preferable, and the melting point of the first thermoplastic resin to the melting point of the first thermoplastic resin + 10 ° C. is even more preferable.

[Thermoplastic resin]
The selection of the first thermoplastic resin and the second thermoplastic resin is not particularly limited as long as the second thermoplastic resin has a higher melting point than the first thermoplastic resin. For example, polyethylene (high density polyethylene / low density) Polyethylene, ultra high molecular weight polyethylene), ultra high molecular weight polyethylene, polypropylene, polystyrene, polyethylene terephthalate, etc., the first thermoplastic resin and the second thermoplastic resin can be selected in consideration of the melting point. it can. Of these, polyethylene resin (especially high-density polyethylene or ultra-high molecular weight polyethylene) is used as the first thermoplastic resin, and polypropylene resin (especially isotactic) is used as the second thermoplastic resin because of the superiority of elastic modulus and bending strength. It is preferable to use tic homopolypropylene).

  The blending ratio of the first thermoplastic resin and the second thermoplastic resin may be appropriately set according to a desired resin molded body, and is not particularly limited. However, the stretching temperature, whiteness, opacity, and bending are not particularly limited. In terms of easy balance between strength and elastic modulus, it is preferably 1: 0.2 to 5, more preferably 1: 0.3 to 3.3, and 1: 0.5 to 2. It is particularly preferred that

The molecular weight distribution Mw / Mn, which is the ratio of the weight average molecular weight Mw and the number average molecular weight Mn of the second thermoplastic resin, is preferably 1 or more and 20 or less, and more preferably 5 or more and 15 or less. The molecular weight distribution Mz / Mn, which is the ratio of the average molecular weight Mz and the number average molecular weight Mn of the second thermoplastic resin, is preferably 10 or more and 100 or less, and more preferably 20 or more and 50 or less. When the molecular weight distributions Mw / Mn and Mz / Mn of the second thermoplastic resin are in the above ranges, it is easy to obtain a resin molded body having an excellent balance between whiteness and opacity, bending strength, and elastic modulus. If the molecular weight distribution is too narrow, the kneadability of the two thermoplastic resins deteriorates, the whiteness and the opacity tend to be nonuniform, and the physical properties of the sheet also become nonuniform. When the molecular weight distribution is too wide, the spot of the melting point becomes wide, so that it becomes difficult to control the stretching temperature and the heat treatment temperature, and it becomes difficult to obtain desired whiteness, opacity, bending stiffness and elastic modulus.

  Further, the molecular weight distribution Mw / Mn, which is the ratio of the weight average molecular weight Mw and the number average molecular weight Mn of the first thermoplastic resin, is preferably 1 or more and 100 or less, and more preferably 10 or more and 40 or less. The molecular weight distribution Mz / Mn, which is the ratio of the average molecular weight Mz and the number average molecular weight Mn of the first thermoplastic resin, is preferably 50 or more and 200 or less, and more preferably 80 or more and 150 or less. When the molecular weight distribution Mw / Mn · Mz / Mn of the first thermoplastic resin is in the above range, it is easy to obtain a resin molded body having an excellent balance of whiteness, opacity, bending strength, and elastic modulus. If the molecular weight distribution is too narrow, the kneadability of the two thermoplastic resins deteriorates, the whiteness and the opacity tend to be nonuniform, and the physical properties of the sheet also become nonuniform. When the molecular weight distribution is too wide, the spot of the melting point becomes wide, so that it becomes difficult to control the stretching temperature and the heat treatment temperature, and it becomes difficult to obtain desired whiteness, opacity, bending stiffness and elastic modulus.

  In the present invention, the weight average molecular weight Mw, the number average molecular weight Mn, and the average molecular weight Mz are measured by a gel permeation (GPC) method.

  The melt mass flow rate (MFR) of the first thermoplastic resin is preferably 0.02 g / 10 or more and 2.0 g / 10 minutes or less, and 0.1 g / 10 or more and 1.0 g / 10 minutes or less. More preferably, when the melt mass flow rate of the first thermoplastic resin is in the above range, it is easy to obtain a resin molded article excellent in balance between whiteness and opacity, bending strength and elastic modulus.

  The melt mass flow rate (MFR) of the second thermoplastic resin is preferably 0.02 g / 10 or more and 2.0 g / 10 minutes or less, and 0.1 g / 10 or more and 1.0 g / 10 minutes or less. Preferably there is. When the melt mass flow rate of the second thermoplastic resin is within the above range, it is easy to obtain a resin molded body having an excellent balance between whiteness and opacity, bending strength, and elastic modulus.

  The melt mass flow rate is an index indicating the fluidity at the time of melting, and means a value measured according to JIS K 7210. As a method for measuring the melt flow rate, specifically, in accordance with JIS K 7210, the melt flow rate was measured under the conditions of a load of 21.18 N, a temperature of 230 ° C. for polypropylene resin, and a temperature of 190 ° C. for polyethylene resin. There is a way to measure.

[Inorganic fine powder]
The blending ratio of the inorganic fine powder is not particularly limited. However, the larger the amount, the more easily the voids are formed during stretching, and the opacity is improved. Preferably, 60 mass% or more is even more preferable. The upper limit of the amount of the inorganic fine powder contained in the entire composition is not particularly limited, but is preferably 80% by mass or less from the viewpoint of kneadability and bending strength.

  The average particle size of the inorganic fine powder is preferably from 0.1 μm to 50 μm, and more preferably from 1.0 μm to 15 μm. When the average particle diameter of the inorganic fine powder is in the above range, it is easy to obtain a resin molded body having an excellent balance between whiteness and opacity, bending strength, and elastic modulus. When the average particle diameter of the inorganic fine powder is too large, the inorganic fine powder is easily detached from the surface of the resin molded body. If the average particle size of the inorganic fine powder is too small, the viscosity increases when kneaded with the thermoplastic resin, and the kneadability tends to deteriorate. The average particle size of the inorganic fine powder in the present invention is a 50% particle size (d50) obtained from a cumulative distribution curve measured with a laser diffraction particle size distribution analyzer.

  Examples of the inorganic fine powder include calcium carbonate, titanium oxide, silica, clay, talc, kaolin, and aluminum hydroxide, and calcium carbonate is particularly preferable. These may be used alone or in combination of two or more. In order to improve the dispersibility or reactivity of the inorganic fine powder, the surface of the inorganic fine powder may be modified in advance according to a conventional method.

  The resin composition of the present invention is selected from lubricants, antioxidants, UV absorbers, pigments for coloring, dispersants, antistatic agents, flame retardants, etc. in addition to the above-described thermoplastic resin and inorganic fine powder 1 More than one kind of auxiliary agent can be added within a range not contrary to the purpose.

  The use of the produced resin molded body is not particularly limited, but is particularly suitable for the balance of whiteness and opacity, bending strength and elastic modulus. For example, printing paper, information paper, packaging, card use ( For example, it is suitable for business cards, processed cardboard, and the like.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

[Reference test]
Samples A and B of calcium carbonate fine powder-filled high-density polyethylene resin sheets were prepared, and changes in optical properties and mechanical properties were evaluated.

  The sheet of Sample A was kneaded directly with a fine powder of calcium carbonate and polyethylene resin at a mass ratio of 60:40 using a twin-screw coaxial extruder, and extruded into a sheet form from a Т die. It produced by extending | stretching on the conditions shown. Sample B was prepared by changing the mass ratio of the fine powder of calcium carbonate and the polyethylene resin to 70:30, extruding into a sheet shape in the same manner as Sample A, and then stretching under the conditions shown in Table 1 below.

  As shown in Table 1, it was found that high opacity can be obtained when the high-density polyethylene resin sheet contains a large amount of calcium carbonate. Moreover, when the draw ratio was increased, the whiteness was remarkably improved and the opacity was slightly improved. On the other hand, Taber stiffness (bending strength) decreased.

[Example 1]
As a first thermoplastic resin, a high-density polyethylene homopolymer (Kyoyo Polyethylene Co., Ltd.) having a molecular weight distribution Mw / Mn = 20.8, a molecular weight distribution Mz / Mn = 121, a melt mass flow rate MFR = 0.3, and a melting point 133 ° C. Manufactured: B5803) (hereinafter referred to as PE). As a second thermoplastic resin, a polypropylene homopolymer (Prime Polymer Co., Ltd.) having a molecular weight distribution Mw / Mn = 10.3, Mz / Mn = 29.1, melt mass flow rate MFR = 0.5, melting point = 165 ° C. ): E111G) (hereinafter referred to as PP) was prepared. Calcium carbonate (manufactured by Shiraishi Calcium: Ryton S4) (hereinafter referred to as CC) was prepared as an inorganic fine powder. These are kneaded directly using a twin-screw coaxial extruder at a feed ratio of PE / PP / CC = 2/2/6, extruded into a sheet form from a Т die at 250 ° C, and cooled with a cast roll at 70 ° C. Solidified to obtain a resin composition. This resin composition was preheated at 125 ° C. and stretched twice in the machine direction. The stretched resin composition was heat treated at 150 ° C., cooled to 30 ° C. and wound up with a winder. Table 2 shows the physical properties of the obtained sheet-like resin molding.

[Example 2]
In the same manner as in Example 1, the first thermoplastic resin, the second thermoplastic resin, and the inorganic fine powder were used in a feed ratio of PE / PP / CC = 2/2/6 using a biaxial coaxial extruder. The mixture was directly kneaded, extruded into a sheet form from a Т die at 250 ° C, and cooled and solidified with a cast roll at 70 ° C to obtain a resin composition. This resin composition was preheated at 125 ° C. and stretched twice in the machine direction. The stretched resin composition was heat treated at 140 ° C., cooled to 30 ° C., and wound up with a winder. Table 2 shows the physical properties of the obtained sheet-like resin molding.

[Example 3]
In the same manner as in Example 1, the first thermoplastic resin, the second thermoplastic resin, and the inorganic fine powder were used in a feed ratio of PE / PP / CC = 2/2/6 using a biaxial coaxial extruder. The mixture was directly kneaded, extruded into a sheet form from a Т die at 250 ° C, and cooled and solidified with a cast roll at 70 ° C to obtain a resin composition. This resin composition was preheated at 125 ° C. and stretched twice in the machine direction. The stretched resin composition was heat-treated at 135 ° C., cooled to 30 ° C. and wound up with a winder. Table 2 shows the physical properties of the obtained sheet-like resin molding.

[Comparative Example 1]
In the same manner as in Example 1, the first thermoplastic resin, the second thermoplastic resin, and the inorganic fine powder were used in a feed ratio of PE / PP / CC = 2/2/6 using a biaxial coaxial extruder. After kneading directly and extruding into a sheet form from a Т die at 250 ° C., cooling and solidifying with a cast roll at 70 ° C., preheating at 125 ° C. and stretching twice in the machine direction. The stretched resin composition was heat treated at 125 ° C., cooled to 30 ° C. and wound up with a winder. Table 2 shows the physical properties of the obtained sheet-like resin molding.

In addition, the physical property of the sheet-like resin molding was measured based on the method shown below.
Density: JIS K 7112
Basis weight: JIS P 8124
Strength at break and elongation at break: JIS K 7162
Tear strength: JIS K 7128-3
Bending stiffness: JIS K 7106
Whiteness: JIS P 8148
Measurement of opacity: JIS P 8149
Smoothness: JIS P 8155
Elastic modulus: JIS K7161

[Evaluation]
From the results in Table 2, the sheet resin molded bodies of Example 1, Example 2, and Example 3 have moderate strengths such as breaking strength, breaking elongation, and tear strength, as in Comparative Example 1. It can be seen that the bending stiffness is improved as compared with Comparative Example 1 while ensuring opacity and whiteness. In particular, it can be seen that the sheet resin molded body of Example 1 is greatly improved in bending strength and elastic modulus as compared with Comparative Example 1.

Claims (4)

A method for producing a resin molded body, comprising:
Mixing a first thermoplastic resin, a second thermoplastic resin having a melting point higher than that of the first thermoplastic resin, and an inorganic fine powder to obtain a resin composition;
Stretching the resin composition below the melting point of the first thermoplastic resin;
Heat-treating the stretched resin composition at a temperature not lower than the melting point of the first thermoplastic resin and lower than the melting point of the second thermoplastic resin.   The method according to claim 1, wherein in the step of obtaining the resin composition, the inorganic fine powder is mixed by 50 mass% or more with respect to the mass of the entire resin composition.   The method according to claim 1 or 2, wherein the first thermoplastic resin is polyethylene and the second thermoplastic resin is polypropylene. The method according to claim 1, wherein the inorganic fine powder contains calcium carbonate.