WATER-SOLUBLE PACKAGING FILM

Abstract

The present invention provides a water-soluble packaging film which is capable of preventing appearance defects such as clouding and deterioration of sealing properties, especially heat sealing properties, over a long period of time and achieving less deterioration and excellent water solubility after packaging. The present invention relates to a water-soluble packaging film containing: a polyvinyl alcohol; a plasticizer; and a dicarboxylic acid containing a hydroxy group, the dicarboxylic acid containing a hydroxy group having a hydroxy group coefficient, which is a quotient of dividing a weight average molecular weight by the number of hydroxy groups, of 90 or more, the film containing the dicarboxylic acid containing a hydroxy group in an amount of 1 to 5 parts by weight.

Claims

1. A water-soluble packaging film comprising: a polyvinyl alcohol; a plasticizer; and a dicarboxylic acid containing a hydroxy group, the dicarboxylic acid containing a hydroxy group having a hydroxy group coefficient, which is a quotient of dividing a weight average molecular weight by the number of hydroxy groups, of 90 or more, the film containing the dicarboxylic acid containing a hydroxy group in an amount of 1 to 5 parts by weight.

2. The water-soluble packaging film according to claim 1, further comprising a dicarboxylic acid containing no hydroxy group.

3. The water-soluble packaging film according to claim 2, containing the dicarboxylic acid containing no hydroxy group in an amount of 0.5 to 3 parts by weight based on 100 parts by weight of the polyvinyl alcohol.

4. The water-soluble packaging film according to claim 1, wherein the polyvinyl alcohol includes a sulfonic acid-modified polyvinyl alcohol.

5. The water-soluble packaging film according to claim 4, containing the sulfonic acid-modified polyvinyl alcohol in an amount of 10 to 100 parts by weight in 100 parts by weight of the polyvinyl alcohol.

6. The water-soluble packaging film according to claim 1, wherein the polyvinyl alcohol further includes a pyrrolidone ring-modified polyvinyl alcohol.

7. The water-soluble packaging film according to claim 6, containing the pyrrolidone ring-modified polyvinyl alcohol in an amount of 0.1 to 50 parts by weight in 100 parts by weight of the polyvinyl alcohol.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0138] FIG. 1 shows a method for producing a tensile specimen for evaluating the retention of sealing strength.

DESCRIPTION OF EMBODIMENTS

[0139] Embodiments of the present invention are further specifically described in the following with reference to, but not limited to, examples.

Example 1

[0140] A 15% by weight polyvinyl alcohol aqueous solution was produced by dissolving in water 75 parts by weight of a sulfonic acid-modified polyvinyl alcohol having a structural unit represented by the formula (1), 25 parts by weight of a pyrrolidone ring-modified polyvinyl alcohol having a structural unit represented by the formula (2), 8 parts by weight of a plasticizer, 2 parts by weight of a hydroxy group-containing dicarboxylic acid, and 1 part by weight of a hydroxy group-free dicarboxylic acid.

[0141] The sulfonic acid-modified polyvinyl alcohol having a structural unit represented by the formula (1) used was a sulfonic acid-modified polyvinyl alcohol having a polymerization degree of 1,200, a saponification degree of 95.4 mol %, and a sulfonic acid-modified amount of 4.0 mol %. R.sup.1 in the formula (1) was a 2-methylene propylene group.

[0142] The pyrrolidone ring-modified polyvinyl alcohol having a structural unit represented by the formula (2) used was a pyrrolidone ring-modified polyvinyl alcohol having a polymerization degree of 1,000, a saponification degree of 95.8 mol %, and a pyrrolidone ring-modified amount of 4.0 mol %.

[0143] The plasticizer in an amount of 8 parts by weight contained 4 parts by weight of glycerol (available from FUJIFILM Wako Pure Chemical Corporation) and 4 parts by weight of diglycerol (available from Sakamoto Yakuhin Kogyo Co., Ltd.). The hydroxy group-containing dicarboxylic acid used was malic acid (available from FUSO CHEMICAL CO., LTD.). The hydroxy group-free dicarboxylic acid used was succinic acid (available from FUSO CHEMICAL CO., LTD.).

[0144] The obtained polyvinyl alcohol aqueous solution was applied to a polyethylene terephthalate (PET) film (thickness: 50 μm) as a support member with an auto film applicator (available from Tester Sangyo Co., Ltd., “PI-1210”), and dried at 80° C. for 5 minutes and then at 100° C. for 20 minutes. Thereby, a sheet of a water-soluble packaging film (thickness: 50 μm) laminated on the support member was obtained.

Example 2

[0145] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 3 parts by weight of malic acid was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

Example 3

[0146] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 25 parts by weight of an unmodified polyvinyl alcohol (polymerization degree: 1,300, saponification degree: 88.0 mol %) was used in place of 25 parts by weight of the pyrrolidone ring-modified polyvinyl alcohol (polymerization degree: 1,000, saponification degree: 95.8 mol %, pyrrolidone ring-modified amount: 4.0 mol %).

Example 4

[0147] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that the pyrrolidone ring-modified polyvinyl alcohol was not added and the amount of the sulfonic acid-modified polyvinyl alcohol added was changed to 100 parts by weight.

Examples 5 to 7 and 9 to 15

[0148] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that the sulfonic acid-modified polyvinyl alcohol, the pyrrolidone ring-modified polyvinyl alcohol, and the unmodified polyvinyl alcohol as shown in Table 1 were used.

[0149] The sulfonic acid-modified polyvinyl alcohol had a structural unit represented by the formula (1), and the pyrrolidone ring-modified polyvinyl alcohol had a structural unit represented by the formula (2).

Example 8

[0150] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 3.3 parts by weight of glycerol and 4.3 parts by weight of diglycerol as plasticizers, 1.5 parts by weight of malic acid as a hydroxy group-containing dicarboxylic acid, and 0.7 parts by weight of succinic acid as a hydroxy group-free dicarboxylic acid were used.

Comparative Example 1

[0151] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 3 parts by weight of citric acid was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

Comparative Example 2

[0152] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Comparative Example 1, except that the pyrrolidone ring-modified polyvinyl alcohol was not added and the amount of the sulfonic acid-modified polyvinyl alcohol added was changed to 100 parts by weight.

Comparative Example 3

[0153] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 3 parts by weight of tartaric acid was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

Comparative Example 4

[0154] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 2 parts by weight of malic acid and 1 part by weight of succinic acid were not added.

Comparative Example 5

[0155] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 0.5 parts by weight of malic acid was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

Comparative Example 6

[0156] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 7 parts by weight of malic acid was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

Comparative Example 7

[0157] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 3 parts by weight of lactic acid was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

Comparative Example 8

[0158] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 4 parts by weight of sodium citrate was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

Comparative Example 9

[0159] A sheet of a water-soluble packaging film (thickness: 50 μm) laminated on a support member was obtained in the same manner as in Example 1, except that 4 parts by weight of acetic acid was used in place of 2 parts by weight of malic acid and 1 part by weight of succinic acid.

(Evaluation)

[0160] Each of the water-soluble packaging films of the examples and comparative examples was peeled off from the support and was then subjected to the following evaluations. Table 1 shows the results.

(1) Appearance Retention Over Time (Haze Measurement)

[0161] The resulting water-soluble packaging film was cut into a 5 cm×5 cm piece to provide a measurement sample. The obtained measurement sample was left in a constant temperature/humidity oven at a temperature of 40° C. and a relative humidity of 85% RH for 10 days.

[0162] The haze value of the resulting film was measured with a haze meter (NDH5000, available from Nippon Denshoku Industries Co., Ltd.).

(2) Sealing Strength Retention

[0163] The resulting water-soluble packaging film was cut into two 10 cm square sheets, and the sheets were left to stand in the same conditions as in the “(1) haze measurement”. The two sheets of the film were then laminated and sealed with a seal tester. The sealing was carried out by pressure bonding at a sealing bar temperature of 140° C. (actual surface temperature: 135° C.), a set pressure of 2.8 kgf/cm.sup.2, and a pressing duration of 0.5 seconds.

[0164] As shown in FIG. 1, a 15 mm-width tensile specimen 3 defined by the dotted line, including a sealed portion 2 (the hatched portion, sealed width: about 1 cm) was cut out from a sheet 1 after sealing. The resulting tensile specimen was pulled at a speed of 100 mm/min and the peeling strength was measured with AUTOGRAPH AGS-H (available from Shimadzu Corporation).

(3) Chemical Resistance (Water Solubility after Packaging)

[0165] The resulting water-soluble packaging film was left to stand in an environment at 23° C. and 50% RH for 15 hours, and was then cut into a 8 cm×14 cm piece. Separately, a sheet of non-woven cloth (made of PE and PP) was cut into a 6 cm×12 cm piece.

[0166] The water-soluble packaging film was folded into half so as to sandwich the sheet of non-woven cloth folded into half. Then, 30 g of trichloroisocyanuric acid tablets (ϕ30 mm×15 mm) were placed in the folded non-woven cloth sheet. Thereafter, three open sides of the water-soluble packaging film were sealed with a width of 1 cm, whereby a packaged product containing the trichloroisocyanuric acid tablets was obtained. The resulting packaged product was placed in a 500-mL glass sealing container and the container was placed in an oven at a temperature of 60° C. for 21 days. The packaged product was then opened and the content was removed, and the film was used as a film for chemical resistance evaluation.

[0167] The film for chemical resistance evaluation was left to stand in an environment at 23° C. and 50% RH for 15 hours, and was then cut into a 3 cm×1.5 cm piece to provide a specimen. The weight (Ws) of the specimen was measured and the specimen was placed in a PE bottle (20 mL). The PE bottle was charged with about 12 ml of water and was then shaken at 180 rpm for 10 minutes. The resulting liquid was filtered with a pre-weighed stainless mesh (Wm, 200 mesh), and the stainless mesh after filtering was dried in an oven at 80° C.

[0168] The stainless mesh was then left to stand in an environment at 23° C. and 50% RH for 15 hours, and the weight (Wt) of the mesh was then measured. The dissolution rate in water was calculated according to the following formula.

Dissolution rate in water (%)=[Ws−(Wt−Wm)]/Ws×100(%)

TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 2 3 4 5 6 7 8 9 PVA resin Sulfonic acid- Polymerization 1200 1200 1200 1200 1200 1200 1200 1200 1150 1200 1200 1200 1150 1600 900 1200 1200 1200 1200 1200 1200 1200 1200 1200 modified degree polyvinyl Saponification 95.4 95.4 95.4 95.4 95.4 95.4 95.4 95.4 95.3 95.4 95.4 95.4 95.8 95.4 95.4 95.4 95.4 95.4 85.4 95.4 95.4 95.4 95.4 95.4 alcohol degree (mol %) Sulfonic acid- 4 4 4 4 4 4 4 4 9 4 4 4 6 4 4 4 4 4 4 4 4 4 4 4 modified amount (mol %) Part by weight 75 75 75 100 60 25 75 75 75 75 35 75 75 75 75 75 100 75 75 75 75 75 75 75 Pyrrolidone Polymerization 1000 1000 — — 1000 1000 1000 1000 1000 1100 — — 1000 1000 1000 1000 — 1000 1000 1000 1000 1000 1000 1000 ring-modified degree polyvinyl Saponification 95.8 95.8 — — 95.8 95.8 95.8 95.8 95.8 95.1 — — 95.8 95.8 95.8 95.8 — 95.8 95.8 95.8 95.8 95.8 95.8 95.3 alcohol degree(mol %) Pyrrolidone 4 4 — — 4 4 4 4 4 6 — — 4 4 4 4 — 4 4 4 4 4 4 4 ring-modified amount (mol %) Part by weight 25 25 — — 20 75 25 25 25 25 — — 25 25 25 25 — 25 25 25 25 25 25 25 Unmodified Polymerization — — 1300 — 1300 — — — — — 700 1600 — — — — — — — — — — — — polyvinyl degree alcohol Saponification — — 85 — 98 — — — — — 95.4 92.0 — — — — — — — — — — — — degree Part by weight — — 25 — 20 — — — — — 15 25 — — — — — — — — — — — — Plasticizer Glycerol Part by weight 4 4 4 4 4 4 4 4 3.3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Diglycerol Part by weight 4 4 4 4 4 4 4 4 4.3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Hydroxy Citric acid Part by weight — — — — — — — — — — — — — — — 3 3 — — — — — — — group- (number containing of carboxyl bi- groups: 3, carboxylic number of OH acid groups: 1, Mw/OH groups: 192) Hydroxy Tartaric acid Part by weight — — — — — — — — — — — — — — — — — 3 — — — — — — group- (number of containing carboxyl di- groups: 2, carboxylic number of OH acid groups: 2, Mw/OH groups: 75) Malic acid Part by weight 2 3 2 2 2 2 2 1.5 2 2 2 2 2 2 2 — — — — 0.5 7 — — — (number of carboxyl groups: 2, number of OH groups: 1, Mw/OH groups: 134) Hydroxy Lactic acid Part by weight — — — — — — — — — — — — — — — — — — — — — 3 — — group- (number containing of carboxyl mono- groups: 1, carboxylic number of OH acid groups: 1, Mw/OH groups: 90) Hydroxy Acetic acid Part by weight — — — — — — — — — — — — — — — — — — — — — — — 4 group-free (number mono- of carboxyl 4 carboxylic groups: 1, acid number of OH groups: 0, Mw/OH groups: - ) Hydroxy Succinic acid Part by weight 1 — 1 1 1 1 1 0.7 1 1 1 1 1 1 1 — — — — — — — — — group-free (number di- of carboxyl carboxylic groups: 2, acid number of OH groups: 0, Mw/OH groups: - ) Hydroxy Sodium citrate Part by weight — — — — — — — — — — — — — — — — — — — — — — 4 — group- (number containing of carboxyl di- groups: 3, carboxylic number of OH acid salt groups: 1, Mw/OH groups: 258) Evaluation Appearance Haze (%) 3 12 8 4 11 6 4 3 15 5 14 12 8 4 4 32 29 37 3 3 25 3 40 7 result retention over time Retention of Sealing strength 7.5 0.7 7.2 5.3 7.0 7.1 7.5 8.7 7.0 6.3 6.5 7.2 7.5 7.2 2.9 2.6 2.2 7.1 7.1 2.3 7.2 1.8 7.3 sealing (N/15 mm) strength Chemical Dissolution resistance rate in water 87 88 91 81 85 80 88 90 82 85 89 91 83 90 85 71 73 75 42 48 85 45 80 35 (%)

INDUSTRIAL APPLICABILITY

[0169] The present invention can provide a water-soluble packaging film which is capable of preventing appearance defects such as clouding and deterioration of sealing properties, especially heat sealing properties, over a long period of time and achieving less deterioration and excellent water solubility after packaging.