JP3264018B2 - Polyvinyl chloride crosslinked foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosslinked polyvinyl chloride foam which is suitable for materials such as automobile interior materials and bags and is used for secondary molding such as vacuum molding and press molding.

[0002]

2. Description of the Related Art A two-layer sheet in which a crosslinked polyvinyl chloride foam is used as a foam layer and a surface (decorative) layer is laminated on the foam layer is widely used as a cover material for automobile interior parts and the like. This sheet is highly evaluated as being suitable for a processing method such as vacuum forming, which is an economical processing method, in addition to a soft texture, cushioning property, design property, and durability. In recent years, with the reduction in the weight of automobiles, the demand for weight reduction of automobile interior parts and the like has increased, and even for polyvinyl chloride-based cross-linked foams used for foam layers, higher foaming has been desired. In addition, since a hot press working method having a higher productivity (short cycle time) than the vacuum forming method has been adopted, a foam having workability suitable for the hot press working method has been required.

However, a foam having a high foaming property and suitable for hot press working, that is, a foam having a high strength of a foam cell and a high closed cell ratio has not been obtained. That is, for high foaming of polyvinyl chloride-based cross-linked foam, the main component is a vinyl chloride copolymer, a plasticizer, a chemical foaming agent, and a polyisocyanate-based cross-linking agent obtained by an emulsion polymerization method or a fine suspension polymerization method. JP-B-52-16948, JP-B-53-5068 and the like describe a foamable vinyl chloride resin composition to be formed and a method of molding the composition into a high-foamed body of 20 times or more. Since the foam obtained here has a low cross-linking rate and a low closed cell rate, in hot press processing or the like in which the processing temperature is 190 ° C. or higher, cell crushing and settling at the time of processing occur, resulting in poor molding. (Sheet breakage, wrinkles, etc.) in many cases.

In the above method, if the plasticizer is simply reduced or the amount of the crosslinking agent is simply increased for the purpose of improving the cell strength, the crosslinking reaction occurs rapidly.
Not only is the desired expansion ratio not obtained, but also the surface smoothness of the foam is remarkably deteriorated, the foam cell structure becomes nonuniform, and other problems occur. Only inadequate things were obtained. Japanese Patent Application Laid-Open No. 4-216833 discloses a method for producing a crosslinked foamed sheet by adding and mixing a modifying agent for the purpose of improving shape retention during heat processing and avoiding molding defects. According to this method, shape retention after molding can be improved while reducing defects during molding, but the practical expansion ratio is 10%.
In order to reduce the weight, it was necessary to improve the magnification by one more step.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyvinyl chloride-based crosslinked foam which has high foaming property and hardly causes molding failure even during hot press working.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a polyvinyl chloride crosslinked resin having a crosslinking ratio of 98% or more, a plasticizer of 20 to 50 parts by weight per 100 parts by weight of the resin, and 0.1 to 0.5 parts by weight of the resin. It mainly consists of 2 to 5 parts by weight of a stabilizer and has an apparent density of 0.05 to 0.08 at a closed cell ratio of 75% or more.
g / cm ³ in a polyvinyl chloride crosslinked foam.
This foam is made of a vinyl chloride copolymer having a hydroxyl group in the molecule (hereinafter abbreviated as “hydroxyl group-containing PVC”) as a plasticizer,
It can be manufactured by mixing with a polyisocyanate crosslinking agent, a chemical foaming agent, and a stabilizer, shaping into a sheet or the like, and heating. In the heating step, crosslinking occurs due to the reaction between the hydroxyl group of the hydroxyl group-containing PVC and the polyisocyanate, and at the same time, the chemical foaming agent is decomposed to form a porous body.

Hereinafter, the present invention will be described in detail. The foam of the present invention mainly comprises a polyvinyl chloride-based crosslinked resin having a crosslinking ratio of 98% or more, a plasticizer of 20 to 50 parts by weight, and a stabilizer of 0.2 to 5 parts by weight based on 100 parts by weight of the resin. It consists of The “crosslinking ratio” in the present invention is defined as the amount of the crosslinkable component (portion that does not dissolve in tetrahydrofuran) of the polyvinyl chloride-based crosslinked resin in the foam, the amount of the crosslinkable component contained in the raw material (the amount of hydroxyl group-containing PVC). And the amount of the polyisocyanate-based cross-linking agent).

The term "consisting mainly of" means that the proportion of the total amount of the polyvinyl chloride-based crosslinked resin and the plasticizer in the foam to the foam is 70% by weight or more, preferably 80% by weight or more. It is in that. The foam of the present invention contains additives commonly used in polyvinyl chloride-based compositions, that is, fillers such as calcium carbonate, titanium white (titanium oxide), other pigments / colorants, and flame retardants. can do. The content of these additives in the foam is 30
% By weight, preferably 20% by weight or less.

The polyvinyl chloride crosslinked resin can be obtained by reacting a hydroxyl group-containing PVC with a polyisocyanate crosslinker. The hydroxyl group-containing PVC is obtained by copolymerizing a vinyl chloride monomer and a comonomer having a hydroxyl group in a molecule which can be copolymerized with the vinyl chloride monomer. Hydroxyl-containing PV
As C, a copolymer containing a hydroxyl group in a molecule (hereinafter abbreviated as “hydroxyl group-containing paste PVC”) obtained by an emulsion polymerization method or a fine suspension polymerization method is particularly preferable.
This is because the paste PVC is composed of fine particles, and the uniform dispersibility of other components for producing a foam is improved. Therefore, it is possible to obtain a foam having a high crosslinking rate and a favorable cell structure. It is thought that it is possible.

The comonomers having a hydroxyl group in the molecule used herein include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4 (or 3) -hydroxybutyl (meth) acrylate, ethyl- Examples thereof include 2-hydroxyethyl maleate and hydroxybutyl vinyl ether, and one or a mixture of two or more thereof is used.

The comonomer content in the hydroxyl group-containing PVC is preferably 0.5 to 10% by weight. If the amount is less than 0.5% by weight, the number of reactive sites capable of crosslinking is too small, and the crosslinking rate is hardly increased. Conversely, if the amount exceeds 10% by weight, the crosslinking reaction is too rapid and its control becomes difficult. The average degree of polymerization of the hydroxyl group-containing PVC is in the range of 700 to 2000.
It is suitable in terms of foaming properties, and the bulk density is preferably in the range of 0.3 to 0.7 (g / cm ³ ) in order to ensure fluidity when the plasticizer is charged.

The plasticizer used in the foam of the present invention includes plasticizers usually used for vinyl chloride polymers, for example, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, butyl benzyl phthalate. Phthalic acid diesters such as isononylbenzyl phthalate, tri-2-ethylhexyl trimellitate, triisodecyl trimellitate and other trimellitic acid triesters, fatty acid diesters such as di-2-ethylhexyl adipate, or phthalic acid, One or a mixture of two or more polyester plasticizers obtained by polycondensing adipic acid or the like with a diol can be used.

[0013] The amount of the plasticizer used is a hydroxyl group-containing PVC 10
20 to 50 parts by weight, preferably 30 parts by weight, per 0 parts by weight
To 45 parts by weight. If the amount is less than 20 parts by weight, the fluidity deteriorates significantly at the time of shaping by extrusion or the like, and crosslinking and foaming occur at this stage due to internal heat generation, which adversely affects subsequent molding. On the other hand, if the amount of the plasticizer exceeds 50 parts by weight, the cross-linking rate and the closed cell rate of the foam after crosslinking and foaming decrease, and the desired foam having good hot press workability cannot be obtained.

The polyisocyanate crosslinking agent includes various diisocyanate monomers such as hexamethylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate and isophorone diisocyanate;
It refers to urethane prepolymers and adducts having terminal isocyanate groups obtained by the reaction of these diisocyanate monomers with polyols, and polyisocyanate polymers containing isocyanurate rings obtained by polymerizing diisocyanate monomers.

Examples of the polyols constituting the urethane prepolymer and the adduct, ie, reacting with the diisocyanate monomer, include polyfunctional alcohols such as ethylene glycol, propylene glycol, glycerin and trimethylolpropane. The polyisocyanate polymer containing an isocyanurate ring is prepared by polymerizing the above-mentioned diisocyanate monomer in a phthalic acid ester or other plasticizer using a catalyst such as a tertiary amine or an alcoholate.

For the purpose of the present invention, it is preferable to use a blocked polyisocyanate cross-linking agent in which the isocyanate group is protected by an alcohol or a phenol.
When a non-blocked body is used, the crosslinking reaction proceeds faster than foaming occurs, and the surface smoothness of the foam deteriorates, or
The desired expansion ratio cannot be obtained, and the closed cell ratio is often insufficient. As a blocking agent for producing a blocked polyisocyanate, for example, hexylphenol,
Nonylphenol, methyl ethyl ketoxime, ε-caprolactam and the like can be mentioned.

As the blocked polyisocyanate-based crosslinking agent, those having a dissociation temperature in the range of 120 to 160 ° C. are preferable. For example, a prepolymer of hexamethylene diisocyanate or isophorone diisocyanate and trimethylolpropane (molar ratio: 3) / 1),
Those blocked with nonylphenol are suitable. When a blocked polyisocyanate crosslinking agent having a dissociation temperature of less than 120 ° C. is used, all of the foamed surface smoothness, the expansion ratio, and the closed cell ratio tend to deteriorate, though not as much as the non-blocked product. The dissociation temperature is 160 ° C
When a blocked polyisocyanate-based cross-linking agent is used, the cross-linking is delayed more than foaming, a sufficient cross-linking rate is not achieved, and the physical properties of the foam tend to be insufficient.

The amount of the cross-linking agent used depends on the target cross-linking rate.
3 to 10 parts by weight, preferably 3 to 100 parts by weight of C
It is preferable to use ６6 parts by weight. If the amount of the cross-linking agent is less than 3 parts by weight, the cross-linking speed is low, and the cross-linking rate becomes insufficient. If the amount of the crosslinking agent exceeds 10 parts by weight, the crosslinking ratio does not increase in proportion to the amount added, and the thermal stability of the foam tends to decrease.

The crosslinking rate of the foam of the present invention must be 98% or more. If the cross-linking ratio is less than 98%, the strength of the cell membrane of the foam (which is considered to be proportional to the thickness and hardness of the cell and the degree of polymerization of the vinyl chloride polymer constituting the cell) is insufficient, and the cell collapse during molding and this Molding is likely to occur. The closed cell rate of this foam needs to be 75% or more. The closed cell ratio is the ratio of the volume of closed cells (bubbles that do not have a communication hole with the outside of the foam) in the total volume of the foam portion of the foam, and is measured using, for example, a device such as an air-comparison hydrometer. It is possible. If the closed cell ratio is less than 75%, the "stiffness" of the foam becomes weak, especially in the case of hot pressing.
The upper and lower sides of the cell membrane compressed at the time of pressurization come into contact with each other, and even after the pressure is released, the foam is crushed and cannot be recovered.

The higher the closed cell rate is, the more preferable. However, if foaming is performed until the apparent density becomes 0.05 to 0.08 g / cm ³ (corresponding to about 15 to 25 times as the expansion ratio), the cell membrane becomes thin. Because of this, it is easy to form an opening (communication hole), and the obtained closed cell rate is generally up to about 90%. The apparent density of this foam is 0.05 to 0.0
8 (g / cm ³ ). When the apparent density exceeds 0.08 g / cm ³ , one of the objects of the present invention of reducing the weight is not sufficiently achieved. Further, if foaming is performed until the amount becomes less than 0.05 g / cm ³ , the cell membrane becomes too thin, the closed cell ratio is reduced, and the cells are liable to be crushed at the time of hot pressing, resulting in molding failure. It will be easier.

Examples of the chemical foaming agent include azo compounds such as azodicarbonamide, hydrazide compounds such as 4,4'-oxybisbenzenesulfonylhydrazide, and other known chemical foaming agents. Further, in order to obtain a foam having a low apparent density, which is the object of the present invention, although it depends on the amount of generated gas of the foaming agent to be used, a hydroxyl group-containing PV is usually used.
For every 100 parts by weight of C, 10 to 20 parts by weight of a chemical blowing agent is used.

The method for producing the crosslinked foam of the present invention from the above-mentioned raw materials will be described. For the stirring and mixing (blend), a kneading machine usually used for processing polyvinyl chloride, for example, a crusher, a ribbon blender, a super mixer, or the like can be appropriately used. The shaping is performed using a molding machine according to the shape of the final product, but when used for automobile interior materials, it is preferable to use an extruder, a calender, or the like, which can be formed into a sheet shape. For example, in the case of forming a sheet by an extruder, the die temperature is preferably set to 110 to 120 ° C. If the temperature is too low, the sheet becomes brittle, and if it is too high, uncontrollable crosslinking / foaming occurs at this stage. As a result, a good foam cannot be obtained.

The crosslinking / foaming by heating is preferably carried out at a high temperature for a short time, for example, at 220 to 230 ° C. for 1 to 3 times.
About a minute is preferred. When this condition is shaken toward a low temperature and a short time, the expansion ratio and the cross-linking ratio are insufficient, and conversely, at a high temperature and a long time, the closed cell ratio is reduced and the product is liable to be colored. Hereinafter, the present invention will be described using examples,
The content of the present invention is not limited by the examples unless it exceeds the gist.

[0024]

EXAMPLES A foam was prepared according to the following formulation and procedure, and the foam was evaluated by the method described below. All parts in the description are parts by weight on a pure basis. <Formulation>

[0025]

TABLE 1 Hydroxyl-containing paste PVC 100 parts (Vinika (registered trademark) paste P100 manufactured by Mitsubishi Kasei Vinyl Co., Ltd.) Plasticizer (diisodecyl phthalate) Predetermined amount * Chemical blowing agent (azodicarbonamide) 12 Stabilizer (Ba-Zn) Liquid stabilizer) 3 Crosslinking agent * Predetermined amount * Stearic acid 0.5 *: described in Table-1

<Preparation of Foam> (1) Blend First, powder components (a hydroxyl group-containing paste PVC, a chemical foaming agent, and stearic acid) are charged into a supermixer of a constant-speed stirring heated to 120 ° C. (constant). . The liquid components (plasticizer, stabilizer, polyisocyanate-based cross-linking agent) that had been previously mixed and homogenized were gradually added thereto with stirring, and uniformly mixed to prepare a powdery foamable composition. .

(2) Forming Using a twin-screw extruder set at a die temperature of 120 ° C. (constant) and a 60-mesh screen, the foamable composition prepared above was supplied, and an unfoamed gelled sheet (0 0.7 mm thick). (3) Foaming The obtained gelled sheet was heated in a hot air oven at 220 to 230 ° C for 90 to 120 seconds to perform three-dimensional foaming.
The heating time was adjusted according to the composition so that the expansion ratio was about 20 times.

<Evaluation method> (1) Apparent density The weight and thickness of a sample piece (prepared if necessary) punched out into a fixed size (area) are measured for both the gelled sheet and the foam. It is calculated by dividing the weight by the volume determined by the product of the area and the thickness. (2) Expansion ratio The ratio of the apparent density of the obtained foam to the density of the gelled sheet was taken as the expansion ratio.

(3) Crosslinking rate The foam was weighed and then immersed in tetrahydrofuran (THF).
The mixture is stirred (replace the THF in the morning and evening; a total of three days and nights), the uncrosslinked portion (including a plasticizer and the like) is removed as a THF-soluble matter, and the insoluble portion is vacuum-dried to determine its weight (Wc). The content of the crosslinkable component (hydroxyl-containing PVC + crosslinking agent) calculated from this Wc and the initial weight and formulation (however, the chemical blowing agent is not counted as decomposing and gasifying).
o) as a percentage (Wc / Wo × 100).

(4) Closed cell ratio The volume of the foam sample is measured in advance (for example, using the method described in (1)), and then the foam is subjected to an air-comparison specific gravity meter manufactured by Beckman. The volume of the closed cell portion is measured using a (930 type). After subtracting the volume of the cell membrane equivalent part from each measured value, the two values were calculated by comparing them.

(5) Heat-resistant press resistance Using a frame having a thickness of 0.25 mm with respect to the thickness of the foam (about 2 mm) (compression rate: about 88%), sandwiching the foam with a press plate preheated to 190 ° C., 50 kg / Cm ² · G (5.0 MPa) for 10 seconds, and then take out. The thickness of the sample before and after pressing was measured, and expressed as a residual ratio of the thickness (the ratio of the thickness after pressing to the original foam thickness (%)).
In order to be able to hot press work, heat press resistance is 80%
The above is desirable.

(6) High-Temperature Tensile Properties A sample piece punched with a JIS No. 1 dumbbell was heated at 140 ° C.
The test was performed at a tensile speed of 500 mm / min, and the elongation (the ratio of the length at break to the initial length) and the 50% modulus were measured. In order to prevent breakage or the like due to deformation during hot pressing, the elongation is preferably 100% or more.

<Evaluation Results> As shown in Table 1, the foam of the present invention (Examples 1 to 3) has a heat resistance of 85% or more, a high temperature property (elongation) of 110 to 180% or more, Press working is possible. Foams having a crosslinking ratio / closed cell ratio outside the range of the present invention (Comparative Examples 1 and 2) have insufficient heat-resistant press properties and high-temperature properties.

[0034]

[Table 2]

[0035]

As described above, by using the crosslinked foam of the present invention, (1) toughness (the thickness residual ratio after hot pressing is 85% or more) and good high-temperature physical properties, A high heat press working method can be applied, and (2) light weight (expansion ratio: about 20 times = approximate density: about 0.06 g / cm ³ ), so that the effect of being useful, for example, for reducing the weight of automobiles can be obtained. .

Continuation of the front page (56) References JP-A-50-123163 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/06 C08L 27/06

Claims (6)

(57) [Claims] 1. A polyvinyl chloride frame having a crosslinking ratio of 98% or more.
20-50 parts by weight of the bridge resin and 100 parts by weight of the resin
Plasticizer and 0.2 to 5 parts by weight of stabilizer
And the apparent density is 0.05 to
0.08g / cm ^ThreeIs a crosslinked polyvinyl chloride foam. 2. The foam according to claim 1, wherein the polyvinyl chloride crosslinked resin is obtained by reacting a vinyl chloride copolymer having a hydroxyl group in a molecule with a polyisocyanate crosslinker. 3. A poly (vinyl chloride) -based crosslinked resin is formed by a block copolymer with a vinyl chloride copolymer having a hydroxyl group in a molecule obtained by an emulsion polymerization method or a fine suspension polymerization method (hereinafter abbreviated as “hydroxyl group-containing paste PVC”). 2. A compound obtained by a reaction with a functionalized polyisocyanate-based crosslinking agent.
The foam as described. 4. 100 parts by weight of a hydroxyl group-containing paste PVC, 20 to 50 parts by weight of a plasticizer, 10 to 20 parts by weight of a chemical foaming agent, and 3 to 10 of a blocked polyisocyanate crosslinking agent.
The method for producing a foam according to claim 1, wherein the foamable composition containing, as a main component, parts by weight and 0.2 to 5 parts by weight of a stabilizer is heated after shaping. 5. The method for producing a foam according to claim 4, wherein a blocked polyisocyanate-based crosslinking agent having a block dissociation temperature in the range of 120 to 160 ° C. is used. 6. The method for producing a foam according to claim 4, wherein the shaping is performed by a calendering method or an extrusion molding method.