JP2024138976A - Vinyl chloride resin composition for powder molding - Google Patents

Abstract

[Problem] To provide a vinyl chloride resin composition for powder molding that can achieve both excellent fogging properties and cold resistance. [Solution] The vinyl chloride resin composition for powder molding contains a polyester plasticizer and a vinyl chloride resin, and the polyester plasticizer is a vinyl chloride resin composition for powder molding that is characterized in that the content of components having a molecular weight of less than 500 as measured by gel permeation chromatography is 2 area % or less. [Selected Figure] None

Description

The present invention relates to a vinyl chloride resin composition for powder molding.

In the automotive manufacturing industry, passenger airbag units are structurally integrated with panels such as vehicle interior panels, door panels, dashboards, and instrument panels. The structural integration of the passenger airbag units to the panels is achieved by a rigid carrier. A foam layer, typically 5-10 mm thick, is placed on top of the rigid carrier and is made of compressible foam to give the panel a soft feel and to smooth out the uneven surface of the underlying carrier. A decorative skin, typically 1-1.5 mm thick, is placed on top of the foam layer and is made of pliable polyvinyl chloride (PVC), sprayable urethane elastomer materials, thermoplastic elastomers, thermoplastic olefins, thermoplastic polyurethanes, and the like. The PVC skin is typically produced using slush molding. Specifically, PVC compound particles are first fed into a heated mold, which is then continuously turned over to melt and sinter the PVC compound particles on the hot mold surface. The PVC particles are sintered to form a sheet that is cooled and then removed from the mold. Slush molding of PVC compounds is disclosed, for example, in U.S. Pat. No. 4,562,025. An alternative to slush molding for producing PVC skins is deep drawing, where a flexible PVC foil or sheet is molded into the desired shape.

However, such skins must meet many stringent criteria for application to vehicle panels, including color stability, dimensional stability under long term UV exposure at elevated temperatures and conditions, resistance to a wide variety of chemicals such as detergents, human body fluids, etc. Also, a major challenge for such skins is that they must be capable of rapid release to allow for rapid and clean release of the passenger airbag contained beneath the foam layer through an opening in the rigid carrier. To facilitate this release, the skins typically have lines of weakness or tear seams that tear or break under the forces of airbag inflation.
Over time, the technology to produce such tears has evolved significantly with changing design criteria and increasingly stringent safety standards imposed on the automotive manufacturing industry. In the past, passenger airbag compartment covers were designed as separate objects placed on top of the airbag compartment, but modern automotive design has evolved toward instrument panels with smooth, continuous visible surfaces with built-in airbag compartments. To avoid tear seams becoming visible over time, the skins must have good resistance to aging when exposed to heat and/or UV for extended periods of time.

However, recent design requirements that require the weakened line or tear seam of the airbag to remain invisible and to withstand aging are balanced against safety standards imposed by the industry that require the skin to be able to release the passenger airbag quickly and cleanly along the weakened line within milliseconds to allow rapid deployment of the airbag. Another important safety criterion is that the skin-foam-carrier sandwich structure should break without scattering particles along the weakened line when the airbag bursts through the cover in all operating conditions that the vehicle may encounter. The flying or heading at high speed of fragments from the skin, foam or carrier towards the passenger should be minimized and remain below a certain limit in all circumstances. A skin with such characteristics, using a specific tear accelerator, is described in Patent Document 1.

WO2017/046166

However, the above safety standards must be met over a wide range of temperatures, at least between -35°C and 80°C, for the instrument panel or any other type of panel containing an airbag in a vehicle.
Furthermore, the skin is required to have not only low temperature resistance but also excellent fogging resistance. However, the vinyl chloride resin molded article obtained by powder slush molding the conventional vinyl chloride resin composition has room for improvement in terms of low temperature resistance and fogging resistance.

The present invention was made in consideration of the above-mentioned circumstances, and its purpose is to provide a vinyl chloride resin composition for powder molding that can achieve both excellent fogging properties and cold resistance.

Means for Solving the Problems The present inventors have conducted intensive research in view of the above problems and have found that it is possible to achieve both good fogging properties and good cold resistance by powder molding a vinyl chloride resin composition that uses a specific polyester plasticizer as a plasticizer.
The present invention has been achieved based on these findings and has the following gist.

[1] A vinyl chloride resin composition for powder molding comprising a polyester plasticizer and a vinyl chloride resin, wherein the polyester plasticizer has a content of components having a molecular weight of less than 500 as measured by gel permeation chromatography of 2 area % or less.
[2] The vinyl chloride resin composition for powder molding according to [1], wherein the polyester plasticizer is a polymer composed of a polycarboxylic acid compound and a glycol, and the glycol has a straight chain portion from a carbon atom bonded to one hydroxyl group of the compound to a carbon atom bonded to another hydroxyl group, the straight chain portion having 2 or more and 5 or less carbon atoms.

[3] The vinyl chloride resin composition for powder molding according to [1] or [2], wherein the glycol-derived structure constituting the polyester-based plasticizer has a structure derived from 1,4-butanediol and 1,2-propanediol.
[4] The content of the polyester plasticizer is 10 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the vinyl chloride resin. [1] to [3]. The polyvinyl chloride resin composition for powder molding according to any one of the above.
[5] An instrument panel comprising the vinyl chloride resin composition for powder molding according to any one of [1] to [4].

According to the present invention, a vinyl chloride resin composition for powder molding can be provided as a powder slush powder containing a vinyl chloride resin that can achieve both fogging properties and cold resistance.

The present invention will be described in detail below, but the present invention is not limited to the following description, and can be modified as desired without departing from the gist of the present invention. In this specification, when a numerical value or physical property value is enclosed before and after "~", the values before and after the "~" are included.
The present invention relates to a vinyl chloride resin composition for powder molding, which contains a polyester plasticizer and a vinyl chloride resin and can be used as a powder slush powder containing a vinyl chloride resin.

[Vinyl chloride resin composition for powder molding]
<Vinyl chloride resin>
The vinyl chloride resin used in the present invention refers to a polymer of a monomer containing a vinyl chloride monomer, and the type is not limited as long as it is a homopolymer of a vinyl chloride monomer or a copolymer of a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer.

Examples of monomers copolymerizable with the vinyl chloride monomer include vinyl esters such as vinyl acetate, vinyl propionate, and vinyl laurate; acrylic esters such as methyl acrylate, ethyl acrylate, and butyl acrylate; methacrylic esters such as methyl methacrylate and ethyl methacrylate; maleic esters such as dibutyl maleate and diethyl maleate; fumaric esters such as dibutyl fumarate and diethyl fumarate; vinyl ethers such as vinyl methyl ether, vinyl butyl ether, and vinyl octyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; α-olefins such as ethylene, propylene, and styrene; vinylidene halides or vinyl halides other than vinyl chloride such as vinylidene chloride and vinyl bromide; and polyfunctional monomers such as diallyl phthalate and ethylene glycol dimethacrylate, but the monomers used are not limited to those mentioned above. These monomers may be used alone or in combination of two or more.

When using a monomer that is copolymerizable with the vinyl chloride monomer in the production of vinyl chloride resins, it is preferable to use the monomer in an amount of 30% by mass or less, and more preferably 20% by mass or less, of the constituent components of the vinyl chloride resin. If it is more than 30% by mass, the inherent performance of the vinyl chloride monomer tends to be lost.

The method for producing the vinyl chloride resin is not particularly limited, and for example, ordinary methods such as suspension polymerization, bulk polymerization, fine suspension polymerization, emulsion polymerization, and solution polymerization can be used. Among these, suspension polymerization is particularly preferred, and the resin is in a powder form that maintains a grain structure (a characteristic structure seen in suspension-polymerized polyvinyl chloride, which has internal porosity. When kneaded, this structure is destroyed and disappears). Since vinyl chloride resin in this state is particularly easy to mix with liquid chemicals, the vinyl chloride resin composition for powder molding of the present invention that uses this resin is suitable for powder slush powder.

The average degree of polymerization of the vinyl chloride resin is preferably 700 to 6,500, more preferably 1,100 to 4,000, based on JIS K6721, in terms of processability, moldability, and physical properties. If the average degree of polymerization is equal to or greater than the lower limit, the physical properties of the resulting vinyl chloride resin composition for powder molding tend to be better, and if it is equal to or less than the upper limit, the processability and moldability tend to be better.

In the present invention, the vinyl chloride resin may be used alone or in combination of two or more vinyl chloride resins differing in copolymerization composition, type of copolymerization monomer, average polymerization degree, etc.
The vinyl chloride resin may be one of commercially available resins or a mixture of two or more of them.

<Polyester-based plasticizer>
The polyester plasticizer is a plasticizer composed of a polyester polymer obtained by polycondensation of a polycarboxylic acid compound and a polyol compound.

The polyol compound is a compound having at least two hydroxyl groups, and is preferably a glycol. The number of carbon atoms in the linear chain from the carbon atom bonded to one hydroxyl group to the carbon atom bonded to the other hydroxyl group of the glycol is preferably 2 to 5. Since the compatibility of the polyol compound with the vinyl chloride resin is affected by the number of carbon atoms, it is preferable to set the number of carbon atoms within this range from the viewpoint of sufficient compatibility.
The number of carbon atoms in the straight chain portion from a carbon atom bonded to one hydroxyl group to a carbon atom bonded to another hydroxyl group includes the carbon atom bonded to the hydroxyl group.
Furthermore, when the glycol has three or more hydroxyl groups, the number of carbon atoms in the straight chain portion from a carbon atom bonded to one hydroxyl group to a carbon atom bonded to another hydroxyl group in this case is the largest number of carbon atoms between carbons bonded to any two hydroxyl groups (including the carbons bonded to hydroxyl groups).

Examples of the glycol include 1,2-ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, and 1,5-pentanediol. In addition, compounds having side chains such as methyl groups and ethyl groups, such as 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, and 3-ethyl-1,5-pentanediol, can be mentioned. Among these, 1,4-butanediol and 1,2-propanediol have better compatibility with vinyl chloride resins, so it is more preferable to use one or both of 1,4-butanediol and 1,2-propanediol.

The polycarboxylic acid compound is a compound having at least two carboxyl groups. Examples of this polycarboxylic acid compound include adipic acid and sebacic acid.

In the present invention, the polyester plasticizer may be used alone or in combination of two or more different polyester plasticizers.
The polyester plasticizer may be a commercially available one or a mixture of two or more kinds.

<Removal of low molecular weight components from polyester plasticizers>
The polyester plasticizer preferably has a small amount of low molecular weight components. Specifically, the content of components with molecular weights of less than 500 as measured by gel permeation chromatography, which will be described later, is preferably 2 area % or less, more preferably 1.5 area % or less, and more preferably 1 area % or less. If it is more than 2 area %, there will be a large amount of components that are easily volatilized, so there is a risk that it will be difficult to obtain sufficient fogging performance. Furthermore, volatilization will occur during the heat aging test, so there is a risk that sufficient low-temperature properties will not be obtained after the heat aging test.

One method for removing low molecular weight components from this polyester plasticizer is to distill off the low molecular weight components by subjecting it to reduced pressure and heat treatment, and this method allows the polyester plasticizer to be purified.

Commercially available polyvinyl chloride contains common plasticizers, but these plasticizers are absorbed into the polyvinyl chloride and do not affect the present invention.

<How to confirm the content of low molecular weight components in polyester plasticizers>
The content of low molecular weight components in the polyester plasticizer can be confirmed by a measurement method using liquid chromatography, specifically, gel permeation chromatography.
Specifically, a size exclusion chromatography column is used as the column, tetrahydrofuran (THF) is used as the mobile phase, and a differential refractive index (RI) detector is used as the detector, and measurements are performed under conditions of a detection wavelength of 254 nm, the area of the resulting graph is calculated, and the content (area ratio) of low molecular weight components (molecular weight of 500 or less) is calculated. The area of the graph of polyester or polyester polymer having a molecular weight of less than 500 is determined by confirming the peak position of polyester or polyester polymer having a molecular weight of about 500, setting the peak position of a molecular weight of 500, and the area of the graph on the lower molecular weight side from that position is the area of polyester or polyester polymer having a molecular weight of less than 500. The molecular weight is calculated in terms of polystyrene.

<Content of polyester plasticizer in vinyl chloride resin composition for powder molding>
The content of the polyester plasticizer in the vinyl chloride resin composition for powder molding is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and more preferably 30 parts by mass or more, based on 100 parts by mass of the vinyl chloride resin. Also, it is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and more preferably 110 parts by mass or less. If the content of the plasticizer is equal to or more than the lower limit, the flexibility imparting effect due to the inclusion of the plasticizer can be fully exerted, and if it is equal to or less than the upper limit, tensile properties can be imparted.

<Additives>
In addition to the vinyl chloride resin and polyester plasticizer, additives such as heat stabilizers and lubricants can be added to the vinyl chloride resin composition for powder molding according to the present invention, if necessary. Examples of the heat stabilizer include perchlorates, light stabilizers such as hindered amine light stabilizers (HALS), initial adhesion inhibitors, light calcium carbonate, zeolite, phenolic antioxidants, zinc stearate, etc. Examples of the lubricant include calcium hydroxystearate and silicone oil.

When a heat stabilizer is contained in the vinyl chloride resin composition for powder molding according to this invention, the content of the heat stabilizer is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, and even more preferably 0.3 to 10 parts by mass, per 100 parts by mass of the vinyl chloride resin. If the content of the heat stabilizer is equal to or greater than the lower limit, the heat stability can be sufficiently exhibited, and if it is equal to or less than the upper limit, the seepage (bloom, bleed) of the additive can be suppressed.

When a lubricant is contained in the vinyl chloride resin composition for powder molding according to the present invention, the content of the lubricant is preferably 0.1 to 5 parts by mass, more preferably 0.3 to 3 parts by mass, and even more preferably 0.5 to 1 part by mass, per 100 parts by mass of the vinyl chloride resin. If the content of the lubricant is equal to or greater than the lower limit, sufficient lubricity can be obtained, and if the content is equal to or less than the upper limit, the exudation (bloom, bleed) of the additive can be sufficiently suppressed.

[Application]
The vinyl chloride resin composition for powder molding according to the present invention can be used in powder slush molding as a powder slush powder containing a vinyl chloride resin to obtain slush molded articles such as instrument panels, door trims, etc.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples as long as it does not exceed the gist of the invention. The various manufacturing conditions and evaluation result values in the following examples are meant as preferred upper or lower limit values in the embodiments of the present invention, and the preferred range may be a range defined by a combination of the above-mentioned upper or lower limit values and the values of the following examples or values between the examples.

[Measurement method]
<Measurement of low molecular weight plasticizers by LC (liquid chromatography)>
From a graph obtained by liquid chromatography (gel permeation chromatography) under the following conditions, the total area and the area of the low molecular weight plasticizer were measured, and the proportion (area ratio) of the low molecular weight plasticizer was calculated.
Column: Size exclusion chromatography column TSK-GEL G3000H,
・Mobile phase: THF (flow rate 1 mL/min),
Column oven temperature: 40° C.
Detector: Differential refractive index (RI) detector, temperature: 40° C., detection wavelength: 254 nm
When diundecyl phthalate (DUP) (molecular weight: 475), a known plasticizer, was measured under these conditions, a peak appeared at 19.5 minutes. Other plasticizers with molecular weights of about 500 also had peaks at about 19.5 minutes, so the area ratio after 19.5 minutes was calculated as the component with a molecular weight (polystyrene equivalent) of less than 500.

<Fogging test>
A vinyl chloride resin molded skin (thickness 1 mm) obtained by the powder slush molding described below was punched out into a circle with a diameter of 80 mm, and placed in a test bottle heated to 110°C using an apparatus conforming to DIN 75 201. A glass plate cooled to 60°C was set at the upper opening of the bottle, and a fogging test was carried out for 5 hours. After the test was completed, the increase in mass of the glass plate before and after the test was determined. In the apparatus, air heated to 110°C by a heater was circulated by a fan.

<Cold resistance test>
A vinyl chloride resin molding skin (thickness 1 mm) obtained by the powder slush molding described below was punched out to a size of 10 x 40 mm, and the peak temperature of the loss modulus was measured (T1) in accordance with JIS K7244-4 at a frequency of 0.21 Hz, a measurement temperature range of -60°C to +30°C, and a heating rate of 2°C/min. In addition, for samples obtained by the urethane foaming preparation described below, the peak temperature of the loss modulus was similarly measured (T2) after completion of a heat aging test (120°C x 400 h). Then, (T2 - T1) / T1 x 100 was defined as the cold resistance change rate (%) before and after the heat aging test.

[Ingredients used]
The raw materials used in the following examples and comparative examples are as follows.
<Vinyl chloride resin>
Polyvinyl chloride: vinyl chloride homopolymer, average degree of polymerization 1300, manufactured by Shin-Etsu Chemical Co., Ltd.: TK1300, having a grain structure (confirmed by scanning electron microscope (SEM)).
Polyvinyl chloride: polyvinyl chloride resin fine particles, particle size 1 to 2 μm, manufactured by Kaneka Corporation: PSM-31.

<Polyester-based plasticizer>
100 parts by weight of the polyvalent carboxylic acid shown below, 60 parts by weight of the glycol shown below, and 30 parts by weight of an end-capping agent (2-ethylhexanol) were mixed in a reaction vessel, an esterification catalyst (tetraisopropyl titanate) was added, and the temperature was raised stepwise from 200°C to 230°C while stirring under a nitrogen stream. This change was monitored by measuring the viscosity of the reaction system with a viscometer and the acid value, hydroxyl value, and water content by chemical analysis at 30-minute intervals, and the reaction was moved to the next stage when it was determined that the progress of the reaction had slowed. In this way, a polyester polymer was produced.
From the obtained polyester polymer, low molecular weight components were removed by distillation under conditions of 5 mmHg and 220° C. As a result, the amounts of components having a molecular weight of less than 500 were as shown below.

Plasticizer A: A polyester-based plasticizer in which the content of components with a molecular weight of less than 500 is less than 2% in the LC measurement below. Plasticizer A-1: Weight average molecular weight: 7,300, components with a molecular weight of less than 500: 1.5%
Polycarboxylic acid compound: adipic acid Glycol: 3-methyl-1,5-pentandiol (3MPD)
Plasticizer A-2: Weight average molecular weight: 4700, components with molecular weight less than 500: 1.3%
Polycarboxylic acid compound: adipic acid Glycol: 1,4-butandiol (14BG) and 1,2-propanediol (12PG) used in a molar ratio of 3:2 Plasticizer A-3: Weight average molecular weight: 5100, components with molecular weight less than 500: 1.4%
Polycarboxylic acid compound: adipic acid Glycol: 1,4-butandiol (14BG) and 2-methyl-1,3-propandiol (2MPD) used in a 1:1 molar ratio

Plasticizer B: A polyester-based plasticizer in which the molecular weight of components less than 500 is 2% or more in LC measurement. Plasticizer B-1: Weight average molecular weight: 6300, molecular weight of components less than 500: 3.0%
Polycarboxylic acid compound: adipic acid Glycol: 1,4-butandiol (14BG) and 2,2-dimethyl-1,3-propandiol (NPG) used in a 1:1 molar ratio Plasticizer B-2: Weight average molecular weight: 5,800, components with molecular weight less than 500: 2.4%
Polycarboxylic acid compound: adipic acid Glycol: 3-methyl-1,5-pentandiol (3MPD)
Plasticizer B-3: Weight average molecular weight: 5100, components with molecular weight less than 500: 3.2%
Polycarboxylic acid compound: adipic acid Glycol: 1,4-butandiol (14BG) and 2-methyl-1,3-propandiol (2MPD) used in a 1:1 molar ratio

<Heat stabilizer>
Heat stabilizer a: Perchlorate (Kyowa Chemical Industry Co., Ltd.: Alcamizer 5)
Heat stabilizer b: Hindered amine light stabilizer (HALS) (ADEKA Corporation: LA63-P)
Heat stabilizer c: Initial adhesion prevention agent (ADEKA: SP-83)
Heat stabilizer d: Light calcium carbonate (Takehara Chemical Industry Co., Ltd.: Neolite SP)
Heat stabilizer e: Zeolite (Mizukarizer DS, manufactured by Mizusawa Chemical Industries, Ltd.)
Heat stabilizer f: Phenol-based antioxidant (AO60 manufactured by ADEKA Corporation)
Heat stabilizer g: Zinc stearate (manufactured by Nitto Kasei Co., Ltd.: ZN-ST)

<Lubricant>
Lubricant h: Calcium hydroxystearate (manufactured by Nitto Kasei Co., Ltd.: CS-6CP)
Lubricant i: Silicone oil (Toray Dow Corning: SH200-60,000CS)

[Examples 1 to 3, Comparative Examples 1 to 3]
<Preparation of vinyl chloride resin composition for powder molding>
The vinyl chloride homopolymer, polyester plasticizer, heat stabilizer and lubricant components shown in Table 1 were charged into a high-speed stirring mixer in the proportions shown in Table 1, and drying was completed when the resin temperature reached 120° C. Thereafter, vinyl chloride resin fine particles shown in Table 1 were added to the dried powder, to obtain a vinyl chloride resin composition for molding as a powder slush powder.

<Powder slush molding>
The powder slush powder (vinyl chloride resin composition for molding) obtained above was melted in a mold heated to 236° C. to prepare a vinyl chloride resin molding skin.

<Urethane foaming>
The polyols and isocyanates were placed in a mixer and mixed for 5 seconds at 5,000 rpm. The mixture was placed in the mold having the vinyl chloride resin molding skin obtained above, and after leaving it for 5 minutes, the molded product was removed, thereby attaching the foamed polyurethane to the vinyl chloride resin molding skin.

[Evaluation Results]
As shown in Table 1, Examples 1, 2, and 3, which used polyester plasticizers A-1, A-2, and A-3, each of which contains less than 2% of components with a molecular weight of less than 500, showed a very good result of a fogging value of 1%. On the other hand, Comparative Examples 1, 2, and 3, which used polyester plasticizers B-1, B-2, and B-3, each of which contains 2% or more of components with a molecular weight of less than 500, showed a poor tendency of a fogging value of 5 to 10%.
Furthermore, the rate of change in cold resistance before and after the heat aging test was 5 to 9% for Examples 1, 2, and 3, which used polyester plasticizers A-1, A-2, and A-3, respectively, in which the molecular weight of components less than 500 was less than 2%, while the rate of change was 14 to 17% for Comparative Examples 1, 2, and 3, which used polyester plasticizers B-1, B-2, and B-3, respectively, in which the molecular weight of components less than 500 was 2% or more, showing a similar tendency to that of the fogging properties.

Claims (5)

A vinyl chloride resin composition for powder molding comprising a polyester plasticizer and a vinyl chloride resin,
The vinyl chloride resin composition for powder molding is characterized in that the polyester plasticizer has a content of components having a molecular weight of less than 500 of 2 area % or less as measured by gel permeation chromatography. The polyvinyl chloride resin composition for powder molding according to claim 1, wherein the polyester plasticizer is a polymer consisting of a polycarboxylic acid compound and a glycol, and the glycol has a straight chain portion from a carbon atom bonded to one hydroxyl group of the compound to a carbon atom bonded to another hydroxyl group, the straight chain portion having 2 to 5 carbon atoms. The vinyl chloride resin composition for powder molding according to claim 1 or 2, wherein the glycol-derived structure constituting the polyester plasticizer has a structure derived from 1,4-butanediol and 1,2-propanediol. The polyvinyl chloride resin composition for powder molding according to claim 1 or 2, wherein the content of the polyester plasticizer is 10 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the polyvinyl chloride resin. An instrument panel made of the vinyl chloride resin composition for powder molding according to claim 1 or 2.