Foamed resin object

Abstract

The present invention aims to provide a resin foam excellent in shock absorption properties and damping properties and less likely to cause sheet misalignment. Provided is a resin foam having a multitude of cells, the resin foam containing: a polyvinyl acetal; and a plasticizer, the resin foam having a loss tangent tan δ with a peak of 0.5 or higher in the range of 0° C. to 50° C. as determined by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz, and the resin foam having a 23° C. compression set of 85% or lower.

Claims

1. A resin foam having a multitude of cells, the resin foam comprising: a polyvinyl acetal; and a plasticizer, the resin foam having an open cell ratio of 20% or higher, and the open cell ratio being defined as the volumetric ratio of cells connected to the outside of the resin foam relative to the apparent volume of the resin foam determined by size measurement, and the resin foam having a loss tangent tan δ with a peak of 0.5 or higher in the range of 0° C. to 50° C. as determined by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz, and the resin foam having a 23° C. compression set of 85% or lower.

2. The resin foam according to claim 1, wherein the resin foam has a loss tangent tan δ with a peak of 0.7 or higher in the range of 0° C. to 50° C. as determined by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz.

3. The resin foam according to claim 1, wherein a temperature range over which the loss tangent tan δ is 0.4 or higher is at least 25° C. as determined by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz.

4. The resin foam according to claim 1, wherein the 23° C. compression set is 50% or lower.

5. The resin foam according to claim 1, crosslinked with a crosslinking agent.

6. The resin foam according to claim 2, wherein a temperature range over which the loss tangent tan δ is 0.4 or higher is at least 25° C. as determined by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz.

7. The resin foam according to claim 2, wherein the 23° C. compression set is 50% or lower.

8. The resin foam according to claim 3, wherein the 23° C. compression set is 50% or lower.

9. The resin foam according to claim 6, wherein the 23° C. compression set is 50% or lower.

10. The resin foam according to claim 2, crosslinked with a crosslinking agent.

11. The resin foam according to claim 3, crosslinked with a crosslinking agent.

12. The resin foam according to claim 6, crosslinked with a crosslinking agent.

13. The resin foam according to claim 4, crosslinked with a crosslinking agent.

14. The resin foam according to claim 7, crosslinked with a crosslinking agent.

15. The resin foam according to claim 8, crosslinked with a crosslinking agent.

16. The resin foam according to claim 9, crosslinked with a crosslinking agent.

Description

DESCRIPTION OF EMBODIMENTS

(1) Embodiments of the present invention are more specifically described in the following with reference to, but not limited to, examples.

Example 1

(2) (1) Production of Resin Foam

(3) To 100 parts by weight of polyvinyl butyral (PVB) were added 40 parts by weight of 3GO, 7 parts by weight of CELLMIC AN (available from Sankyo Kasei Co., Ltd., decomposition temperature: 125° C.), 2 parts by weight of TMPTA (available from Kyoei Kagaku Kogyo), and 0.4 parts by weight of benzophenone, whereby a resin composition was obtained. The obtained resin composition was sufficiently kneaded at 110° C. in a mixing roll and then extruded through an extruder into a sheet having a thickness of 1 mm. The PVB had a hydroxy group content of 34.5 mol %, a degree of acetylation of 0.8 mol %, a degree of butyralization of 64.7 mol %, and average degree of polymerization of 1,700.

(4) Each surface of the obtained sheet was irradiated with ultraviolet light at 1,500 mJ/cm.sup.2 (365 nm) using a high pressure mercury lamp (available from Toshiba Lighting & Technology Corporation, TOSCURE 401), whereby benzophenone was activated to cause crosslinking. The sheet was then put in an oven and the heat-decomposable foaming agent was decomposed at a foaming temperature of 220° C., whereby a resin foam was obtained.

(5) (2) Measurement of Open Cell Ratio and Apparent Density

(6) The open cell ratio of the obtained resin foam was measured by pycnometry in conformity with JIS K 7138. The apparent density was obtained by calculation based on the measured weight and the apparent volume obtained from size measurement.

(7) (3) Measurement of Loss Tangent Tan δ

(8) A foam sample having a thickness of 4 mm was formed, and a piece having a diameter of 2.5 cm was cut out of the sample. The piece was subjected to measurement at varying temperatures with a dynamic viscoelasticity measuring apparatus (ARES-G2, available from TA Instruments) to determine the loss tangent tan δ. The measurement was performed under the conditions of a measurement strain of 1%, a measurement frequency of 1 Hz, and a measurement temperature of −10° C. to 70° C.

(9) (4) Measurement of 23° C. Compression Set

(10) The 23° C. compression set was measured by a method in conformity with JIS K 6262.

(11) Specifically, circular samples having a diameter of 29 mm were cut out and stacked to a thickness of about 12.5 mm. The obtained stack sample was interposed between two parallel flat plates, compressed by 25% of the initial thickness of the sample, and left to stand under standard conditions (23° C. and 50% RH) for 22 hours. The sample was then taken out of the flat plates, left to stand at standard conditions for 30 minutes, and then the thickness was measured again. The compression set was determined by the following equation.
Compression set=(Initial thickness−Thickness after test)/(Initial thickness−Compressed thickness)×100

Examples 2 to 9

(12) A resin foaming agent was produced and the loss tangent tan δ, the 23° C. compression set, and other properties were measured as in Example 1 except that the amounts of the heat-decomposable foaming agent, the crosslinking agent, and the photopolymerization initiator were as shown in Table 1.

Comparative Example 1

(13) A commercially available polyethylene foam (available from Sekisui Chemical Co., Ltd., Softlon S, expansion ratio: 30 times) was provided as a comparative example. The loss tangent tan δ, the 23° C. compression set, and other properties of the polyethylene foam were measured as in Example 1.

Comparative Example 2

(14) A commercially available ethylene-vinyl acetate copolymer (EVA) foam (available from Mitsufuku Industry Co., Ltd., MITSUFUKU FOAM V15, expansion ratio: 12 times) was provided as a comparative example. The loss tangent tan δ, the 23° C. compression set, and other properties of the EVA foam were measured as in Example 1.

(15) (Evaluation)

(16) The resin foams obtained in the examples and comparative examples were evaluated as follows.

(17) Table 1 shows the results.

(18) (1) Evaluation of Shock Absorption Properties (Hammer Test)

(19) A sheet having a thickness of 4 mm formed from the obtained resin foam was used as a sample. This sample was interposed between two polycarbonate (PC) sheets each having a thickness of 2 mm to give a stack. The stack was compressed until the thickness of the resin foam was reduced to 3.6 mm (reduced by 10%). The stack was left to stand in this state for one month at 25° C.

(20) The stack after standing was taken out, and one surface of the stack was hit with a hammer. The magnitude of shock (maximum acceleration) at the front surface (surface hit with a hammer) and the back surface was measured. The magnitude of shock (%) at the back surface was calculated, with the magnitude of shock at the surface hit with a hammer taken as 100%.

(21) (2) Evaluation of Fluidity (Sheet Misalignment Test)

(22) The sample was interposed between PC sheets at 10% compression and left to stand for one month in the same manner as above. The stack was then positioned vertically, and hit with a hammer from one side at a shock value (maximum acceleration) of 1,000 m/s.sup.2. Whether sheet misalignment due to movement of the resin foam occurred was observed. The fluidity was evaluated according to the following criteria. ∘ (Good): No sheet misalignment was observed. x (Poor): Sheet misalignment occurred.

(23) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Resin Thermoplastic Type — PVB PVB PVB PVB PVB PVB composition resin Amount Parts by weight 100 100 100 100 100 100 Plasticizer Type — 3GO 3GO 3GO 3GO 3GO 3GO Amount Parts by weight 40 40 40 40 40 40 Foaming agent Type — CELLMIC CELLMIC CELLMIC CELLMIC CELLMIC CELLMIC AN AN AN AN AN AN Amount Parts by weight 7 10 15 2 7 7 Crosslinking Type — TMPTA TMPTA TMPTA TMPTA TMPTA TMPTA agent Amount Parts by weight 2 2 2 2 0.5 5 Photo- Type — Benzo- Benzo- Benzo- Benzo- Benzo- Benzo- polymerization phenone phenone phenone phenone phenone phenone initiator Amount Parts by weight 0.4 0.4 0.4 4 0.4 0.4 Resin Open cell ratio % 67 88 90 12 65 15 foam Apparent density kg/m.sup.3 170 130 110 500 140 250 Loss tangent Peak — 0.98 0.95 0.98 0.95 0.93 0.83 tanδ Temperature range ° C. 40 42 45 40 45 40 over which tanδ is 0.4 or higher 23° C. compression set % 18 20 22 45 52 20 Evaluation Shock absorption % 52 45 40 60 35 55 (Hammer test) Fluidity evaluation — ∘ ∘ ∘ ∘ ∘ ∘ (Sheet mis- alignment test) Comparative Comparative Example 7 Example 8 Example 9 Example 1 Example 2 Resin Thermoplastic Type — PVB PVB PVB Poly- EVA composition resin Amount Parts by weight 100 100 100 ethylene foam Plasticizer Type — 3GO 3GO 3GO foam Amount Parts by weight 40 40 40 Foaming agent Type — CELLMIC CELLMIC CELLMIC AN AN AN Amount Parts by weight 15 7 10 Crosslinking Type — TMPTA agent Amount Parts by weight 0.5 Photo- Type — Benzo- polymerization phenone initiator Amount Parts by weight 0.4 Resin Open cell ratio % 88 87 90 <2 <2 foam Apparent density kg/m.sup.3 100 140 110 30 80 Loss tangent Peak — 0.95 0.98 0.92 0.35 0.32 tanδ Temperature range ° C. 47 50 45 0 0 over which tanδ is 0.4 or higher 23° C. compression set % 38 73 67 98 97 Evaluation Shock absorption % 35 38 40 105 98 (Hammer test) Fluidity evaluation — ∘ ∘ ∘ x x (Sheet mis- alignment test)

INDUSTRIAL APPLICABILITY

(24) The present invention can provide a resin foam excellent in shock absorption properties and damping properties and less likely to cause sheet misalignment.