JP7687818B2 - Resin composition and extrusion molded product - Google Patents

Description

The present invention relates to a resin composition and an extrusion molded article. In particular, the present invention relates to a material containing polyacetal resin as a main component and used for extrusion molding, and a molded article thereof.

Polyacetal resin is an engineering plastic with an excellent balance of mechanical properties, and is also used as a material for cutting round bars, plates, etc. However, because polyacetal resin is highly crystalline, it shrinks significantly when solidified, and so when it is melted and then molded, voids and whitening are likely to occur inside the molded product, which is undesirable in terms of physical properties and appearance. For example, round bars with large diameters are generally molded by the so-called solidification extrusion method, in which the material is solidified in a cooled die, but in this case voids and whitening are likely to occur in the center. Patent Document 1 describes a resin composition that suppresses the occurrence of these voids and whitening.

JP 2004-323567 A

As described above, Patent Document 1 discloses a resin composition that suppresses the occurrence of voids and whitening. However, with technological innovation, there is a demand for further suppression of the occurrence of voids and whitening, and also for materials with low yellowness (for example, a low b value).
The present invention aims to solve such problems, and has an object to provide a resin composition and an extrusion molded article in which the occurrence of voids and whitening is suppressed and the b value is low.

In view of the above-mentioned problems, the present inventors have conducted research and found that the above-mentioned problems can be solved by adjusting the resin composition so that the entire composition is slowly and uniformly solidified. Specifically, the above-mentioned problems have been solved by the following means.
<1> A resin composition for extrusion molding containing a polyacetal resin, wherein the area from the start of crystallization to the top of a crystallization peak when the resin composition is isothermally crystallized at 148°C is in the range of 40 to 50% of the area of the entire crystallization peak.
<2> The resin composition according to <1>, wherein the time from the start of crystallization to the crystallization peak when isothermally crystallized at 148°C is 50 seconds or more.
<3> The resin composition according to <1>, in which the time from the start of crystallization to the crystallization peak when isothermally crystallized at 148°C is 60 seconds or more.
<4> The resin composition according to any one of <1> to <3>, comprising paraffin wax and/or a polyolefin resin.
<5> The resin composition according to <4>, wherein the polyolefin resin comprises a polyethylene resin.
<6> An extrusion molded article formed from the resin composition according to any one of <1> to <5>.
<7> The extrusion molded body according to <6>, wherein the extrusion molded body is in the form of a round bar or a plate.
<8> The extrusion molded body according to <6> or <7>, wherein the area of the extrusion cross section of the extrusion molded body is 50 to 2000 ^cm2 .

The present invention makes it possible to provide a resin composition and extrusion molded product that suppresses the occurrence of voids and whitening and has a low b value.

FIG. 2 is an image showing the isothermal crystallization time at 148° C. when the resin composition of the present invention was subjected to DSC measurement. FIG. 2 is an image diagram showing the isothermal crystallization time at 148° C. when DCS is measured for a conventional resin composition.

Hereinafter, an embodiment of the present invention (hereinafter, simply referred to as the present embodiment) will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to the present embodiment.
In this specification, the word "to" is used to mean that the numerical values before and after it are included as the lower limit and upper limit.
In this specification, various physical properties and characteristic values are those at 23° C. unless otherwise specified.

The resin composition of this embodiment is a resin composition for extrusion molding that contains a polyacetal resin, and is characterized in that when the resin composition is isothermally crystallized at 148°C, the area from the start of crystallization to the top of the crystallization peak is in the range of 40 to 50% of the area of the entire crystallization peak. By adopting such a configuration, it is possible to provide a resin composition that suppresses the occurrence of voids and whitening and has a low b value.

As mentioned above, polyacetal resin is also used as a cutting material for round bars, plates, etc. However, when a resin composition containing polyacetal resin is melted, extruded into a rod shape such as a round bar or a plate, and solidified, a region called a white core is formed in the center when the cross section is observed. When light is irradiated and observed, the white core is a part that looks white because the way light is scattered changes. When the present inventor investigated the cause of this white core, it was found that, for example, in the case of an extrusion molded product of a round bar, the size of the crystals of the polyacetal resin is different between the center and the outer periphery. More specifically, it was speculated that the crystal size is large. When the resin composition containing polyacetal resin is solidified, as shown in FIG. 2, it was speculated that the conventional one (corresponding to the comparative example) does not solidify uniformly because the crystallization proceeds quickly. In other words, it was speculated that the polyacetal resin has parts that solidify quickly and parts that solidify slowly, and the crystal size is likely to change. In contrast, in the case of the example shown in FIG. 1, crystallization proceeds slowly, so that the size of the crystals tends to be uniform overall, and it is assumed that white cores are less likely to form.
Under these circumstances, it has been found that by setting the area from the start of crystallization to the top of the crystallization peak during isothermal crystallization at 148°C to be in the range of 40 to 50% of the area of the entire crystallization peak, it is possible to provide a resin composition that suppresses the occurrence of voids and whitening and has a low b value.

In Figure 1, 1 is the crystallization start time, 2 is the crystallization end time, and 3 is the crystallization peak top time. The area surrounded by the curve between crystallization start time 1 and crystallization start time 2 and the dotted line connecting crystallization start time 1 and crystallization end time 2 is the area of the entire crystallization peak, and the area from crystallization start time 1 to crystallization peak top time 3 is the area indicated by the diagonal line.

In this embodiment, the area from the start of crystallization to the top of the crystallization peak when isothermal crystallization is performed at 148°C is 40 to 50% of the area of the entire crystallization peak, but 40 to 48% is preferable, 40 to 46% is more preferable, 40 to 44% is even more preferable, and 40 to 43% is even more preferable. By setting it in such a range, the effect of this embodiment can be more effectively exerted.

In this embodiment, the time from the start of crystallization to the top of the crystallization peak when isothermal crystallization is performed at 148°C is preferably 50 seconds or more, more preferably 60 seconds or more, and even more preferably 65 seconds or more. By setting the time to the lower limit or more, it is possible to make it more difficult for white cores to form. The upper limit of the time is, for example, 200 seconds or less, and may be 150 seconds or less. By setting the time to the upper limit or less, it is possible to make it more difficult for vacuum voids to form.

There is no particular requirement for a method for making the area from the start of crystallization to the top of the crystallization peak when the resin composition is isothermally crystallized at 148°C 40-50% of the area of the entire crystallization peak. Any method that can cause the crystallization of the resin composition to proceed within the desired range can be used. Specific examples include adding an additive, particularly adding paraffin wax and/or polyolefin resin (preferably polyethylene resin), and increasing the oxyethylene content of the polyacetal resin.

Next, the polyacetal resin used in this embodiment will be described.
The polyacetal resin is not particularly limited in terms of its type, and may be a homopolymer containing only divalent oxymethylene groups as constituent units, or a copolymer containing divalent oxymethylene groups and divalent oxyalkylene groups having two or more carbon atoms as constituent units.
Examples of the oxyalkylene group having two or more carbon atoms include an oxyethylene group, an oxypropylene group, and an oxybutylene group.

In the polyacetal resin, the ratio of oxyalkylene groups having 2 or more carbon atoms to the total number of moles of oxymethylene groups and oxyalkylene groups having 2 or more carbon atoms is preferably 0.5 to 10 mol %. The number of carbon atoms in the oxyalkylene group may be 2 or more, but is preferably 6 or less, and more preferably 4 or less.
Furthermore, in this embodiment, the ratio of oxyethylene groups to the total number of moles of oxymethylene groups and oxyalkylene groups having 2 or more carbon atoms in the polyacetal resin (oxyethylene content) is preferably 1.2 mol% or more, more preferably 1.3 mol% or more, even more preferably 1.4 mol% or more, even more preferably 1.5 mol% or more, and may be 1.7 mol% or more. The upper limit of the oxyethylene content is preferably 2.5 mol% or less, more preferably 2.4 mol% or less, even more preferably 2.3 mol% or less, and even more preferably 2.2 mol% or less. In particular, by making the oxyethylene content 1.7 mol% or more, the crystallization of the polyacetal resin can be made to proceed slowly.

In order to produce the polyacetal resin, trioxane is usually used as the main raw material. To introduce an oxyalkylene group having 2 to 6 carbon atoms into the polyacetal resin, for example, a cyclic formal or a cyclic ether can be used. Specific examples of cyclic formals include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3,5-trioxepane, and 1,3,6-trioxocane. Specific examples of cyclic ethers include ethylene oxide, propylene oxide, and butylene oxide. To introduce an oxyethylene group into the polyacetal resin, for example, 1,3-dioxolane can be used, to introduce an oxypropylene group, 1,3-dioxane can be used, and to introduce an oxybutylene group, 1,3-dioxepane can be used.

In addition, in a polyacetal resin, it is preferable that the amount of hemiformal end groups, formyl end groups, and end groups unstable to heat, acid, or base is small. Here, a hemiformal end group is represented by -OCH ₂ OH, and a formyl end group is represented by -CHO.

The melt volume rate (MVR) value of the polyacetal resin is preferably 0.5 cm ³ /10 min or more, more preferably 1.0 cm ³ /10 min or more, even more preferably 1.5 cm ³ /10 min or more, and may be 2.0 cm ³ /10 min or more. By setting it to such a value, the load on the motor of the extruder can be reduced, and the productivity of the resin composition (e.g., pellets) can be improved. In addition, the MVR is preferably 4.5 cm ³ /10 min or less, more preferably 4.0 cm ³ /10 min or less, and even more preferably 3.5 cm ³ /10 min or less. By setting it to the upper limit value or less, it is possible to make it more difficult for vacuum voids to occur.
The MVR value of the polyacetal resin (A) means an MVR value measured under conditions of 190° C. and a load of 2.16 kg in accordance with ISO 1133.

The content of the polyacetal resin in the resin composition of this embodiment is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more.
The resin composition of the present embodiment may contain only one type of polyacetal resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Other ingredients>
The resin composition of the present embodiment may contain components other than the polyacetal resin in order to adjust the crystallization speed or to exhibit other functions. Specifically, the other components include nitrogen-containing compounds such as melamine compounds and hydrazine compounds, inorganic fillers, heat stabilizers, antioxidants, weather stabilizers, light resistance stabilizers, ultraviolet absorbers, release agents, lubricants, crystal nucleating agents, antistatic agents, antibacterial agents, colorants (pigments, dyes), etc. These may be used alone or in combination of two or more.
Specifically, in order to adjust the crystallization speed, it is preferable to contain paraffin wax and/or polyolefin resin. An example of the paraffin wax is Paraffin Wax 155 manufactured by Nippon Seiro Co., Ltd. An example of the polyolefin resin is polyethylene resin.
When the resin composition of the present embodiment contains paraffin wax and/or polyolefin resin, the content is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, even more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more, relative to 100 parts by mass of polyacetal resin. The upper limit of the content of the paraffin wax and/or polyolefin resin is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, even more preferably 1.0 parts by mass or less, even more preferably 0.8 parts by mass or less, and even more preferably 0.7 parts by mass or less, relative to 100 parts by mass of polyacetal resin. By making the content less than the upper limit, it is possible to make it more difficult for vacuum voids to occur.
The resin composition of the present embodiment may contain a metal hydroxide, but preferably does not substantially contain a metal hydroxide. The term "substantially does not contain" means that the content of the metal hydroxide is, for example, less than 3 parts by mass, preferably less than 1 part by mass, and more preferably less than 0.5 parts by mass, per 100 parts by mass of the polyacetal resin. By setting the content in such a range, yellowing of the molded product can be more effectively suppressed.

<Method of producing resin composition>
The method for producing the resin composition of the present embodiment is not particularly limited, and can be prepared by various methods conventionally known as a method for preparing a resin composition.For example, (1) a method of mixing all the components constituting the resin composition, feeding them to an extruder and melt-kneading them to obtain a pellet-shaped composition, (2) a method of feeding a part of the components constituting the resin composition from the main feed port of an extruder and the remaining components from the side feed port, melt-kneading them to obtain a pellet-shaped composition, (3) a method of preparing pellets with different compositions once by extrusion or the like, mixing the pellets to adjust to a predetermined composition, (4) a method of mixing a predetermined amount of compounding components with pellets or pulverized material of polyacetal resin, or coating a predetermined amount of compounding components on the surface of pellets or pulverized material of polyacetal resin to obtain a predetermined resin composition, etc. can be adopted.

Next, an extrusion molded article formed from the resin composition of this embodiment will be described. The resin composition of this embodiment is used to produce molded articles of various shapes, such as a round bar or a plate, by extrusion molding. The extrusion molded article of this embodiment is not only used as a product after molding, but is also used to produce various parts and the like by further processing such as cutting. In the case of extrusion molding, unlike injection molding, no mold is used, so cost reduction can be expected depending on the application.
The resin composition of the present embodiment has excellent extrusion moldability, and can significantly reduce voids that are undesirable in terms of physical properties and whitening that is undesirable in terms of appearance that occur inside the extrusion molded product. Therefore, the extrusion molded product formed from the resin composition of the present embodiment has extremely high physical reliability even when it is subsequently cut and molded into a molded product such as a gear or a container. Furthermore, the reduction in voids makes it possible to mold at low pressure, and therefore the moldability is improved, such as the reduction in residual stress of the extrusion molded product.
The resin composition of the present embodiment is particularly suitable for molding a round bar extrusion molded product having a diameter of 10 to 300 mm, a plate-like extrusion molded product having a thickness of 10 to 100 mm, etc. Examples of products that can be molded from the molded product by cutting include gears, containers, screws, etc.
The area of the extrusion cross section of the extrusion molded product is preferably 50 to 2000 ^cm2 .

The present invention will be described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

Raw polyethylene: Novatec LDLJ803, manufactured by Japan Polyethylene Corporation
Paraffin wax: Paraffin wax 155, manufactured by Nippon Seiro Co., Ltd.
Magnesium hydroxide: Kyowa Chemical Industry Co., Ltd., Magsarat F

<Method of measuring melt volume flow rate (MVR) of polyacetal resin>
The MVR was measured under conditions of 190° C. and a load of 2.16 kg in accordance with ISO 1133. The unit is cm ³ /10 min.

Examples 1 to 3, Comparative Examples 1 to 3
<Preparation of polyacetal copolymer (polyacetal resin)>
A desired amount of 1,3-dioxolane was added to 100 parts by mass of trioxane, a benzene solution (0.62 mol/Kg-benzene) of boron trifluoride diethyl etherate as a catalyst in an amount of 0.05 mmol per 1 mol of total monomers, and a benzene solution (25 mass%) of methylal as a molecular weight regulator was added continuously in an amount such that methylal had the MVR shown in Table 1 relative to the total monomers, and polymerization was continuously performed in a twin-screw kneader having a self-cleaning paddle with a jacket whose temperature was set to 65° C. so that the residence time in the polymerization machine was 15 minutes. A benzene solution (25 mass%) of triphenylphosphine was added to the produced polymer so that 2 mol of triphenylphosphine was added per 1 mol of boron trifluoride diethyl etherate added, and the catalyst was deactivated, followed by pulverization to obtain a crude polyacetal copolymer.
In the polyacetal resins 1 to 3, the amount of 1,3-dioxolane was adjusted so that the oxyethylene content was the value shown in Table 1.

<Production of pellets>
The components shown in Table 1 were mixed in the amounts (parts by mass) shown in Table 1 per 100 parts by mass of polyacetal resin using a tumbler blender. The resulting mixture was then melt-kneaded and pelletized in a twin-screw extruder (L/D=30) to obtain pellets (resin composition).

<Time from the start of crystallization to the top of the crystallization peak, and area ratio from the start of crystallization to the top of the crystallization peak relative to the entire crystallization peak>
The time from the start of crystallization to the top of the crystallization peak and the area ratio from the start of crystallization to the top of the crystallization peak to the entire crystallization peak were determined from values measured by DSC (differential scanning calorimetry).
Specifically, the pellets obtained above were crushed, heated from 40° C. to 210° C. at a rate of 320° C./min, and held at 210° C. for 5 minutes, then cooled from 210° C. to 148° C. at a rate of 80° C./min, and held at 148° C. (crystallization onset temperature), to obtain the crystallization peak of each sample.
Furthermore, the area of the crystallization peak was obtained by connecting the crystallization start time and the crystallization end time, and the area ratio from the crystallization start to the crystallization peak top to the entire crystallization peak area was obtained. In addition, the time from the crystallization start to the crystallization peak top was measured. Taking FIG. 1 as an example, 1 is the crystallization start time, 2 is the crystallization end time, and 3 is the crystallization peak top time. The area surrounded by the curve between the crystallization start time 1 and the crystallization start time 2 and the dotted line connecting the crystallization start time 1 and the crystallization end time 2 is the entire crystallization peak area, and the area from the crystallization start time 1 to the crystallization peak top time 3 is the area indicated by the diagonal line.
The DSC measurement device used was a Pyris Diamond DSC manufactured by PerkinElmer.

<Manufacturing of round bars>
The pellets obtained above were used as a raw material to obtain a round bar molded product having a diameter of 100 mm by a solidification extrusion molding machine having a cooling die attached to the head of a no-vent type single screw extruder (L/D = 25). The round bar extrusion molding was performed under the following conditions.

Cylinder temperature: 180-195°C
Die temperature: 195°C
Die cooling temperature: 40°C
Resin pressure: 3.5 to 4.5 MPa

<Lead whitening, voids, b value>
The round bar molded product obtained above was cut into 3 mm slices, and a red micro-check penetrant liquid for detecting metal defects was applied to the cross section, followed by washing with n-hexane. The area of the part penetrated by the liquid was enlarged using a digital microscope to calculate the area, and the area (unit: ^mm2 ) of the region where voids were formed was measured.
The round bar was cut into slices and the presence or absence of whitening was visually confirmed. The results were evaluated as follows. The evaluation was performed by five experts and was based on a majority vote.
A: No whitening B: Slight whitening is observed C: Other than A and B, for example, whitening is clearly observed The b value was measured for slices of the round bar using SE-6000 manufactured by Nippon Denshoku Industries Co., Ltd. under the conditions of C light source and a viewing angle of 2°. At this time, the white core portion was avoided.

As is clear from the above results, the molded articles formed from the resin composition of the present invention had no voids, little or no whitening of the core, and a low b value (Examples 1 to 3).
On the other hand, when the area ratio from the start of crystallization to the top of the crystallization peak to the entire crystallization peak was outside the range of 40 to 50%, voids were generated, whitening of the white core was observed, and the b value was high (Comparative Examples 1 to 3).

1. Crystallization start time 2. Crystallization end time 3. Crystallization peak top

Claims (10)

A resin composition for extrusion molding comprising a polyacetal resin and a paraffin wax and/or a polyolefin resin, and not containing a release agent other than the paraffin wax and/or the polyolefin resin and not containing a melamine compound,
When the resin composition is isothermally crystallized at 148° C., the area from the start of crystallization to the top of the crystallization peak is in the range of 40 to 50% of the entire area of the crystallization peak,
The resin composition is molded into a round bar having a diameter of 100 mm at a cylinder temperature of 180 to 195°C, a die temperature of 195°C, a die cooling temperature of 40°C, and a resin pressure of 3.5 to 4.5 MPa using a solidification extrusion molding machine, and the round bar is cut into 3 mm slices. The b value measured under conditions of a C light source and a viewing angle of 2° is -3 or less. A resin composition for extrusion molding comprising a polyacetal resin and paraffin wax and/or polyethylene , and not containing a release agent other than the paraffin wax and/or polyethylene and not containing a melamine compound,
When the resin composition is isothermally crystallized at 148° C., the area from the start of crystallization to the top of the crystallization peak is in the range of 40 to 50% of the entire area of the crystallization peak,
The content of the polyethylene and the paraffin wax is 0.1 parts by mass or more and 2.0 parts by mass or less relative to 100 parts by mass of the polyacetal resin,
Does not contain melamine compounds, hydrazine compounds, heat stabilizers, antioxidants, weather stabilizers, light stabilizers, UV absorbers, antibacterial agents, or colorants.
A resin composition having a metal hydroxide content of less than 3 parts by mass per 100 parts by mass of a polyacetal resin. A resin composition for extrusion molding comprising a polyacetal resin and a paraffin wax and/or a polyolefin resin, and not containing a release agent other than the paraffin wax and/or the polyolefin resin, and not containing a melamine-formaldehyde polycondensate,
When the resin composition is isothermally crystallized at 148° C., the area from the start of crystallization to the top of the crystallization peak is in the range of 40 to 50% of the entire area of the crystallization peak,
The resin composition was molded into a round bar having a diameter of 100 mm using a solidification extrusion molding machine at a cylinder temperature of 180 to 195°C, a die temperature of 195°C, a die cooling temperature of 40°C, and a resin pressure of 3.5 to 4.5 MPa, and then cut into 3 mm slices. No whitening was observed.
The resin composition is molded into a round bar having a diameter of 100 mm at a cylinder temperature of 180 to 195°C, a die temperature of 195°C, a die cooling temperature of 40°C, and a resin pressure of 3.5 to 4.5 MPa using a solidification extrusion molding machine, and the round bar is cut into 3 mm slices. The b value measured under conditions of a C light source and a viewing angle of 2° is -3 or less. A resin composition for extrusion molding comprising a polyacetal resin and paraffin wax and/or polyethylene , and not containing a release agent other than the paraffin wax and/or polyethylene , and not containing a melamine-formaldehyde polycondensate,
When the resin composition is isothermally crystallized at 148° C., the area from the start of crystallization to the top of the crystallization peak is in the range of 40 to 50% of the entire area of the crystallization peak,
The resin composition was molded into a round bar having a diameter of 100 mm using a solidification extrusion molding machine at a cylinder temperature of 180 to 195°C, a die temperature of 195°C, a die cooling temperature of 40°C, and a resin pressure of 3.5 to 4.5 MPa, and then cut into 3 mm slices. No whitening was observed.
The content of the polyethylene and the paraffin wax is 0.1 parts by mass or more and 2.0 parts by mass or less relative to 100 parts by mass of the polyacetal resin,
Does not contain melamine compounds, hydrazine compounds, heat stabilizers, antioxidants, weather stabilizers, light stabilizers, UV absorbers, antibacterial agents, or colorants.
A resin composition having a metal hydroxide content of less than 3 parts by mass per 100 parts by mass of a polyacetal resin. The resin composition according to any one of claims 1 to 4, in which the time from the start of crystallization to the peak of crystallization when isothermally crystallized at 148°C is 50 seconds or more. The resin composition according to any one of claims 1 to 4, in which the time from the start of crystallization to the peak of crystallization when isothermally crystallized at 148°C is 60 seconds or more. The resin composition according to claim 1 or 3 , wherein the polyolefin resin comprises a polyethylene resin. An extrusion molded article formed from the resin composition according to any one of claims 1 to 7. The extrusion molded body according to claim 8, wherein the extrusion molded body is in the form of a round bar or a plate. The extrusion molded body according to claim 8 or 9, wherein the extrusion cross-sectional area of the extrusion molded body is 50 to 2000 ^cm2 .