(19)
(11)EP 3 725 859 A1

(12)EUROPEAN PATENT APPLICATION

(43)Date of publication:
21.10.2020 Bulletin 2020/43

(21)Application number: 19305493.9

(22)Date of filing:  16.04.2019
(51)International Patent Classification (IPC): 
C09J 9/00(2006.01)
C08K 5/04(2006.01)
C09J 11/08(2006.01)
(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
KH MA MD TN

(71)Applicant: Société BIC
92110 Clichy (FR)

(72)Inventor:
  • BETHOUART, Carine
    62152 Neufchatel Hardelot (FR)

(74)Representative: Cabinet Beau de Loménie 
158, rue de l'Université
75340 Paris Cedex 07
75340 Paris Cedex 07 (FR)

  


(54)GLUE STICK COMPOSITION


(57) The present invention concerns a water based glue stick composition comprising adhesive and nanocrystalline cellulose. It also concerns a glue stick containing the glue stick composition according to the present invention and the use of a glue stick for planar joining of substrates, in particular for joining paper and/or cardboard, to one another, in particular printer paper, photo paper and cardboard paper.


Description


[0001] The present invention concerns glue stick with improved gluing performance, in particular by the use of additives which are not detrimental to the environment and to the health of the consumer.

[0002] Glue sticks are rod-shaped adhesives that are received slidably in a closable casing and leave behind a tacky film when rubbed off onto a substrate surface. They contain an adhesive dissolved in a liquid phase together with shape-imparting structural substance. The substance mixture is solidified in the form of a more or less rigid soap gel having a rod-like stick form which upon rubbing-off will be converted into a pasty state having a good adhesive nature.
Glue sticks having no negative impact on the environment are already known in the art such as in US2017/0226393. In this case starch derivatives are used as the adhesive.
However, there is still a need to improve the gluing performance of such a glue stick without impairing the environment and while maintaining an acceptable stick length.
The inventors have surprisingly discovered that by the use of nanocrystalline cellulose it is possible to solve the above-mentioned problem without impairing the consistency of the composition which will hold and retain its shape. Moreover there will be less deposit of the glue stick on the paper (in g/100m) which will allow a longer use of the glue stick for the same glue stick length than the glue stick of the prior art.

[0003] The present invention therefore concerns a water based glue stick composition comprising adhesive and nanocrystalline cellulose.

[0004] For the purposes of the present invention, the term "water based" is intended to mean that water is the main solvent of the composition. As a consequence the glue stick composition comprises at least 40 weight % of water, based on the total weight of the composition.
In particular, the water content of the glue stick composition according to the present invention is comprised between 40 and 70 weight %, preferably in the range 45-60 weight %, and more preferably in the range 48-55 weight %, based on the total weight of the glue stick composition. In an advantageous manner, the glue stick composition is free of organic solvent.

[0005] The glue stick composition according to the present invention contains an adhesive which will provide the glue stick composition with its adhesive properties.
Advantageously the adhesive is selected in the group consisting of starch, starch derivatives, polyvinylpyrrolidone, aqueous polyacrylates, polyvinyl alcohols and mixture thereof. More advantageously the adhesive is selected in the group consisting of starch, starch derivatives and mixture thereof. Indeed these particular adhesives are more environmentally friendly. Still more advantageously the adhesive is starch such as cereal starch (for example corn, wheat or rice starch) or tuber or root starch (for example potato, cassava or tapioca starch) or legume starch (for example pea or bean starch); more particularly it is corn starch which can be available commercially at Roquette under the trade name Tackidex 250. In an advantageous manner, the glue stick composition is free of polyvinylpyrrolidone. Starch derivatives can be dextrin and/or starch based sugar and/or starch ether such as hydroxyalkylcarboxymethyl starch (such as described in CA2826831).

[0006] Advantageously, the adhesive content of the glue stick composition according to the present invention is in the range 15-35 weight % based on the total weight of the glue stick composition, more advantageously in the range 17-32 weight % based on the total weight of the glue stick composition, still more advantageously in the range 22-27 weight % based on the total weight of the glue stick composition.

[0007] The glues stick composition also contains nanocrystalline cellulose (CNC). Cellulose is the most abundant natural polymer available on the earth and it is an important structural component of the cell wall of various plants. Apart from plants, cellulose is also present in a wide variety of living species, such as algae, fungi, bacteria, and even in some sea animals such as tunicates. Cellulose is composed of β-1,4-linked glucopyranose units that form a high-molecular-weight linear homopolymer, in which every monomer unit is corkscrewed at 180° with respect to its neighbors. The repeating unit of this natural polymer is a dimer of glucose, known as cellobiose. The degree of polymerization of cellulose can vary depending on the source and it is approximately 10,000 glucose units for wood-derived cellulose and 15,000 units for cotton-derived cellulose. Each glucopyranose unit bears three hydroxyl groups, which impart cellulose some of the characteristic properties such as hydrophilicity, chirality, biodegradability, etc., which are initiated by the high reactivity of the hydroxyl groups. The ability of these hydroxyl groups to form strong hydrogen bonds is the main reason for some other properties such as multiscale microfibrillated structure, hierarchical organization (crystalline and amorphous fractions), and highly cohesive nature. Naturally occurring bulk cellulose consists of highly ordered, crystalline regions along with some disordered (amorphous) regions in varying proportions, depending on its source. When these microfibrils are subjected to a proper combination of mechanical, chemical, and enzyme treatments, the highly crystalline regions of the cellulose microfibrils can be extracted, resulting in the formation of cellulose nanocrystals called nanocrystalline cellulose (CNCs). CNCs are stiff rod-like particles consisting of cellulose chain segments in a nearly perfect crystalline structure. Several mechanical processes, such as high-pressure homogenizations, high-intensity ultrasonic treatments, microfluidization techniques, cryocrushing, etc., have been utilized for the extraction of cellulose microfibrils. These mechanical processes produce enough shear forces to split apart the cellulose fibers along the longitudinal axis and help to extract the cellulose microfibrils. Each cellulose microfibril is devoid of chain folding and can be considered a string of cellulose crystals, linked along the microfibril by disordered or paracrystalline regions. The chemical method of converting cellulose microfibrils into CNCs is better than the mechanical methods as the former reduces energy consumption and also produces rod-like short nanocrystals with improved crystallinity. Strong acid hydrolysis is usually used for the removal of amorphous domains that are regularly distributed along the microfibrils. Strong acids can easily penetrate into the amorphous regions having a low level of order and hydrolyze them, leaving the crystalline regions unaffected.
As a consequence, advantageously the nanocrystalline cellulose according to the present invention is obtained by strong acid hydrolysis of cellulose (such as HCI or sulfuric acid or phosphoric acid hydrolysis), more advantageously by sulfuric acid hydrolysis of cellulose, still more advantageously the nanocrystalline cellulose consists in cellulose hydrogen sulphate salt nanoparticles, in particular cellulose hydrogen sulphate sodium salt nanoparticles. More advantageously, the nanocrystalline cellulose according to the present invention is not oxidized. In particular the surface charge of the nanocrystalline cellulose according to the present invention is not reduced by desulfation (DS) in post-treatment after sulfuric acid hydrolysis.
In a particular embodiment the source of cellulose of the nanocrystalline cellulose according to the present invention is a plant such as wood cotton, jute, ramie, sisal, flax, or hemp, water plants, grasses, agricultural wastes such as wheat and rice straw, sugarcane bagasse, sawdust, cotton stables, more advantageously the source of cellulose is wood or cotton, such as wood pulp or cotton fibers, still more advantageously it is wood, in particular wood pulp.
In an advantageous embodiment the nanocrystalline cellulose according to the present invention is spindle shaped.
Advantageously the nanocrystalline cellulose according to the present invention has a particle diameter in the range 2-8 nm, preferably in the range 2 - 5 nm, in particular in the range 2.3-4.5 nm, measured by atomic force microscopy (AFM).
In an advantageous manner, the nanocrystalline cellulose according to the present invention has a particle length in the range of 40-160 nm, preferably in the range 44-108 nm, measured by atomic force microscopy. Advantageously the crystalline fraction of the nanocrystalline cellulose according to the present invention is 0.88 measured by X-ray powder diffraction (XRD). The nanocrystalline cellulose according to the present invention can be available commercially at CelluForce under the trade name CelluForce NCC.
In an advantageous embodiment, the nanocrystalline cellulose content of the glue stick composition according to the present invention is in the range 0.1-3 weight % based on the total weight of the glue stick composition, advantageously in the range 0.2-2 weight % based on the total weight of the glue stick composition, more advantageously in the range 0.25-1.5 weight % based on the total weight of the glue stick composition.

[0008] The water based glue stick composition according to the present invention can also contain other components.
In an advantageous embodiment, the water based glue stick composition according to the present invention comprises a humectant, advantageously selected in the group consisting of glycerin, sorbitol, aloe Vera, honey, propylene glycol, butylene glycol and mixture thereof, more advantageously selected in the group consisting of glycerin, sorbitol and mixture thereof, still more advantageously it is a mixture of sorbitol and glycerin.
Advantageously the humectant content of the glue stick composition according to the present invention is in the range 5-30 weight % based on the total weight of the glue stick composition, more advantageously in the range 10-25 weight % based on the total weight of the glue stick composition, still more advantageously in the range 15-20 weight % based on the total weight of the glue stick composition.

[0009] The water based glue stick composition according to the present invention can also contain a soap, advantageously selected in the group consisting of sodium salt of fatty acid, more advantageously sodium salt of C12-C22 fatty acids, still more advantageously sodium salt of C14-C18 fatty acids, in particular it is sodium stearate. The soap is the shape-imparting structural substance of the glue stick composition according to the present invention.
Advantageously the soap content of the glue stick composition according to the present invention is in the range 1-20 weight % based on the total weight of the glue stick composition, more advantageously in the range 2-15 weight % based on the total weight of the glue stick composition, still more advantageously in the range 2-5 weight % based on the total weight of the glue stick composition.
The water based glue stick composition according to the present invention can contain other additives, advantageously selected in the group consisting of antifoam agent, preservative, perfume, pH regulators, pH indicators, lubricants, wetting agents, plasticizers, fillers, superabsorbers, coloring agents such as dyes or pigments or mixture thereof and mixture thereof, more advantageously selected in the group consisting of antifoam agent, preservative and mixture thereof, in particular in a content well known by the one skilled in the art.
Advantageously the additives content of the glue stick composition according to the present invention is in the range 0.1-7 weight % based on the total weight of the glue stick composition, more advantageously in the range 1-5 weight % based on the total weight of the glue stick composition, still more advantageously in the range 2.5-3.5 weight % based on the total weight of the glue stick composition.
In particular the glue stick composition according to the present invention may comprise an antifoam agent, preferably a polysiloxane-based antifoam agent or a silica and oil blend (such as Foamaster MO2170 from BASF), and more preferably an aqueous emulsion of modified polysiloxane (such as MOUSSEX® from Synthron, TEGO® Foamex from Evonik).
Advantageously the antifoam agent content of the glue stick composition according to the present invention is in the range 0.5-3 weight % based on the total weight of the glue stick composition, more advantageously in the range 1-2.5 weight % based on the total weight of the glue stick composition, still more advantageously in the range 1.15-2.15 weight % based on the total weight of the glue stick composition

[0010] The glue stick composition according to the present invention may contain a preservative such as phenoxyethanol (ACTICIDE® from Thor), isothiazolinone advantageously selected in the group consisting of 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and mixture thereof.
Advantageously, the preservative is present in the glue stick composition according to the invention in an amount ranging from 0.03 to 1.5 weight %, more advantageously ranging from 0.05 to 1 weight %, relative to the total weight of the glue stick composition.
The lubricants can be polyalkylene glycol derivatives, such as polyoxyethylene lauryl ether, fatty acid alkali salts, nonionic surfactants, fluorine base surfactants such as perfluoroalkyl ether phosphoric acid esters and polyether modified silicone such as polyethylene glycol adducts of dimethylenepolysiloxane.
The filler can be mineral filler such as barium sulfate, or it can be gelatin or sucrose.
The pH regulator can be ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of phosphoric acid such as tripolyphosphate, sodium carbonate and hydroxides of alkali metals such as sodium hydroxide.
The pH indicator can be thymolphthalein.
The present invention also concerns the glue stick containing the glue stick composition according to the present invention, advantageously having a rod-like stick form. In particular the length of the glue stick (8 g) is comprised between 6-7 cm. The present invention also concerns a casing containing the glue stick according to the present invention, advantageously with a cap. More advantageously the casing is a twist or push-up tube.

[0011] It also concerns the use of a glue stick according to the present invention for planar joining of substrates, in particular for joining paper and/or cardboard, to one another, in particular printer paper, photo paper and cardboard paper.
It also concerns a process of preparation of the glue stick comprising the following steps:

a- Mixing under heating below 100°C, advantageously at a temperature between 85-90°C, water, the optional humectant and/or antifoam agent, nanocrystalline cellulose, the adhesive, the soap and the optional additive such as the preservative and/or the antifoam agent;

b- Pouring the preparation obtained in step a) into the sticks;

c- Letting the stick cool at room temperature until solidification;

d- Recovery of the glue stick thus obtained.

Advantageously, the speed of the mixing of step a) is higher during the addition of the adhesive and the soap.
In an advantageous manner, water, the optional humectant and/or antifoam agent are first mix together before the addition of nanocrystalline cellulose under stirring. The adhesive is then added under stirring, before the addition of the soap under stirring and finally the rest of the optional additive.

[0012] The present invention will be understood more clearly in the light of the examples which follow, which are given in a non-limiting way.

Example 1: preparation of a glue stick according to the invention



[0013] Two different glue sticks have been prepared having the composition described in table 1 below
Table 1
 Formula 1Formula 2Function
Water 51.15 52.40 Solvent
Glycerine 4810 (glycerin) 10.00 10.00 Humectant
Neosorb 70/70 (sorbitol) 7.15 7.15 Humectant
Tackidex 250 (corn starch) 25.50 24.50 Adhesive
Sodium stearate 3.00 3.50 Soap
Celluforce NCC (nanocrystalline cellulose) 1.00 0.25 Additive
Foamaster MO2170 (Silica and oil blend) 1.30 1.30 Additive (antifoam agent)
Acticide PHE (phenoxyethanol) 0.90 0.90 Additive (preservative)
Total 100.00% 100.00%  


[0014] The process of preparation for the composition of formula 2 is as follow:

- 1st step: Mixing (85 - 90°C)



[0015] Laboratory equipment = Dissolver DISPERMAT® LC75 - Dissolver disc Ø 60 mm.

[0016] For a laboratory preparation of 300 g, we heat between 85-90°C 157.2 g of water and then introduce 30 g of Glycerine 4810 + 21.45 g of Neosorb®70/70 and 2.40 g of Foamaster® MO2170. We stir at 500 rpm speed during 5 min and maintain the temperature between 85-90°C.

[0017] We add under stirring 0.75 g of Cellulose NCC and maintain 500 rpm speed and the same temperature during 5 min.

[0018] We increase the stirring speed to 1000 rpm and introduce at this stage 73.50 g of TACKIDEX® 250.

[0019] We stir during 15 min and maintain the temperature at 85-90°C.

[0020] We add 10.50 g of sodium stearate and stir during 15 min without changing stirring speed and temperature.

[0021] At the end, we add 2.70 g of Acticide® PHE and 1.50 g of Foamaster® MO2170 and stir only 3 min at lower stirring speed (500 rpm).

- 2nd step: Filling (80°C)



[0022] We pour immediately the preparation into the sticks.

- 3rd step: Cooling (65°C to room T°C)



[0023] We let the sticks solidified at room temperature.

[0024] The same preparation process is used for preparing a glue stick of formula 1 with the corresponding amount of each ingredient.

Example 2: comparison of the gluing performances with a glue stick not containing nanocrystalline cellulose



[0025] The gluing performance of the glue stick having the composition of formula 2 of example 1 has been compared with the gluing performance of the glue stick having the same composition but without nanocrystalline cellulose (comparative formula 2 of example 1) and prepared as described in example 1 by the use of the following tests (Table 2).
Table 2
 Formula 2 of example 1Comparative formula 2 of example 1Function
Water 52.40 52.65 Solvent
Glycerine 4810 (glycerin) 10.00 10.00 Humectant
Neosorb 70/70 (sorbitol) 7.15 7.15 Humectant
Tackidex 250 (corn starch) 24.50 24.50 Adhesive
Sodium stearate 3.50 3.50 Soap
Celluforce NCC (nanocrystalline cellulose) 0.25 - Additive
Foamaster MO2170 (Silica and oil blend) 1.30 1.30 Additive (antifoam agent)
Acticide PHE (phenoxyethanol) 0.90 0.90 Additive (preservative)
Total 100.00% 100.00%  


[0026] The stick length (= total length placed) and the glue quantity used by 100m (= weight of glue necessary to glue 100 meters of paper) have been assessed by using the following method at 23°C and 50%RH, 7 days after manufacturing the glue stick, on 3 sticks of glue for each example:
  1. 1- The glue stick in the tube is weighted (with the cap)
  2. 2- Then the glue is placed by strips of 20cm of Paper A4 80g/m2 of reference Navigator or equivalent (= printer paper) in order to completely empty the tube of glue.
  3. 3- The empty glue stick tube is weighted (with the cap).


[0027] Steps 1 to 3 are repeated with the 2 other glue sticks and the average is calculated.

[0028] For each tested glue stick, the number of pages totally covered and the length covered on the last page is determined, in order to be able to determine the total length placed, by using the following formula:



[0029] The weight of glue necessary to glue 100 meters of paper is calculated using the following formula:



[0030] The setting time (= bonding time) has been assessed by using the following method at 23°C and 50%RH on a paper A4 80g/m2 of reference Navigator or equivalent, 7 days after manufacturing the glue stick, on 5 sticks of glue for each example:

1- On a sheet of scrap paper, make a deposit to check whether it is uniform.

2. Cut 2 strips of paper 80g/m2 of 4 cm in width and 12 cm in length, then 2 strips of paper 80g/m2 of 4 cm in width and 15 cm in length

3. On the 1st strip of paper of 15 cm, place 2 layers of glue superimposed on the center of the strip.

4. Position the 1st strip of 12 cm on the strip of 15 cm and apply pressure like a customer does when he glues 2 pieces of paper together (pressure with fingers on the assembling after glue deposit).

5. When the test specimen is produced, start the chronometer.

6. Every 5 seconds, gradually pull off the two paper strips until there is breakage between the 2 supports.



[0031] Beyond 30 seconds, perform the test every 10 seconds instead of 5 seconds.

[0032] The bonding time of a glue corresponds to the breakage between the 2 supports.

[0033] If the bonding time is greater than 2 minutes, indicate > 2 minutes.

[0034] In the case where a single test specimen has not been sufficient, repeat the test using two new strips (12 and 15 cm), starting to pull off the two strips later.

7. Repeat steps 3 to 6 for the 2nd strips of paper.

8. Repeat steps 2 to 7 for the other glue stick to be tested.



[0035] The "Customer test" (= Quality of bonding of a glue stick over time Consumer Test) has been assessed by using the following method at 23°C and 50%RH, one day and 7 days after manufacturing the glue stick ( Consumer Test 1 day), or 1week and 7 days after manufacturing the glue stick (Consumer Test 1 week) on 5 sticks of glue for each example:
The equipment consists in:
  • Spiral notebook 60g/m2 of reference Lyreco Budget 210 X 297 mm, 80 pages or equivalent
  • Paper A4 80g/m2 of reference Navigator or equivalent (=printer paper)
  • Stiff-covered paper 200g/m2 of reference Canson Mix Media Imagine or equivalent (= cardboard paper)
  • Photo paper 250 g/m2 of reference HP Advanced or equivalent (= photo paper)
  • Standardised roll of 1 kg
  • Standardised roll of 2 kg.


[0036] The method is as follow:
  1. 1. On a sheet of scrap paper, make a deposit to check whether it is uniform.
  2. 2. Cut 8 strips of paper 80g/m2 of 4 cm in width and 12 cm in length.
  3. 3. On the 1st strip of paper, make a glue deposit (1 layer) on the center of the strip and glue it on the notebook sheet (do not glue strips on the back of notebook sheets).
  4. 4. Apply pressure with the 1 kg standardised roller (1 forward-return pass, where the glue was deposited).
  5. 5. Repeat steps 3 to 4 for the 7 other strips of 80g/m2 paper.
  6. 6. Immediately close the notebook after gluing.
  7. 7. Repeat steps 2 to 6 for the other supports to be tested and for the other products to be tested.
  8. 8. Store the notebook in an air-conditioned room at 23°C / 50% RH.
  9. 9. After 1h of test, and for each paper support to be tested, pull the first paper strip to determine the type of adherence encountered during tear-off. This test corresponds to the ageing interval T0.
  10. 10. Repeat step 9 for the next 7 bands, after each ageing interval.
  11. 11. Repeat steps 1 to 10 with the 2 kg standardised roller and with applying pressure like a customer does when he glues 2 pieces of paper together (pressure with fingers on the assembling after glue deposit = consumer usage).


[0037] The scoring obtained is as follow:

10 : The paper strip has fully adhered to the notebook sheet - The support breaks;

7.5: The paper strip has partially adhered to the notebook sheet - The support partially breaks;

5: The paper strip adheres slightly to the notebook sheet - The support partially does not tear;

2.5: The paper strip adheres very slightly to the notebook sheet - The support does not tear and slight resistance is felt - Cohesive break

0: The paper strip does not adhere at all to the notebook sheet - The support does not tear - Cohesive break



[0038] The results are indicated in table 3 below:
Table 3
 Formula 2 of example 1Comparative formula 2 of example 1
Stick length (m) 45.6 34.6
Glue quantity used by 100 m (g/100m) 16.0 20.4
Setting time (s) Consumer usage 50 55
Consumer Test 1 day Roll (1 kg) Printer paper 5 5
Photo paper 7.5 7.5
Cardboard paper 2.5 2.5
Roll (2 kg) Printer paper 10 7.5
Photo paper 10 10
Cardboard paper 7.5 5
Consumer usage Printer paper 10 10
Photo paper 10 10
Cardboard paper 10 7.5
Consumer Test 1 week Roll (1 kg) Printer paper 10 2.5
Photo paper 7.5 5
Cardboard paper 2.5 0
Roll (2 kg) Printer paper 10 10
Photo paper 10 10
Cardboard paper 7.5 7.5
Consumer usage Printer paper 10 10
Photo paper 10 10
Cardboard paper 10 2.5


[0039] Cardboard paper and photo paper are known to be more difficult to glue. It should be noted that the results obtained with the roll of 2 kg is close to the results obtained with the fingers (the roll of 1 kg is lighter than the fingers). As shown in table 3, the glue stick according to the present invention (formula 2) shows better results in term of stick length, glue quantity used by 100m and consumer tests, in particular after 1 week and on cardboard paper.

[0040] Therefore the gluing performance of a glue stick containing the nanocrystalline cellulose is better than the gluing performance of a glue stick not containing nanocrystalline cellulose.

Example 3: comparison of the gluing performances with comparatives glue stick not containing nanocrystalline cellulose.



[0041] The gluing performance of the glue stick having the composition of formula 1 of example 1 has been compared with the gluing performance of comparative example 2 and of comparative example 3 having the composition indicated in the following tables 4 and 5.
Table 4
 Comparative example 2Function
Water 53.4 Solvent
Glycerin 8.0 Humectant
Monopropylene glycol 0.6 Humectant
Starch 28.0 Adhesive
Sodium stearate 10.0 soap
Total 100.00%  
Table 5
 Comparative example 3Function
Water 46.0 Solvent
Polyvinyl pyrrolidone 22.0 Adhesive
Sodium stearate 7.00 soap
Glycerin 11.0 Humectant
Propylene glycol 4.0 Humectant
Other 10.0 Biocide, perfume
Total 100.00%  


[0042] Each glue stick has been tested on 3 different types of paper (Printer paper 80 g/m2, Canson paper 200 g/m2 (cardboard paper) and Photo paper 250 g/m2) by making for each type of paper, a glue deposit on one side of the paper and add another paper on the glue deposit and then apply pressure with the 1 kg standardised roller (4 forward-return pass, where the glue was deposited). Peeling tests have been performed on each glued papers at 23°C and 50%RH at 180° with a speed of 300mm/min using the Standard method Finat FTM 1: peel adhesion (180°) at 300 per minute until the tearing of the paper according to the following method:
The unglue side of the papers is fixed on a metal plate engaged in the top jaw of the tensile apparatus. An extension is added to the leading edge (end of the glued paper). It is engaged in the lower jaw.

[0043] The evolution of the peeling linear load is drawn as a function of the shift. The failure mode is identified (adhesive, cohesive, tearing of the paper...) Tests specimen dimension are 25 mm x 175 mm in machine direction. The results are indicated in table 6 below:
Table 6
ReferencesPrinter paper 80 g/m2Canson paper 200 g/m2 (cardboard paper)Photo paper 250 g/m2
Comparative Example 2 85 (+/- 20) N/m 70 (+/- 30) N/m 90 (+/- 20) N/m
Comparative Example 3 < 40 N/m < 20 N/m Null
Formula 1 105 (+/- 20) N/m 100 (+/- 15) N/m 100 (+/-20) N/m


[0044] The adhesion degree is higher for the glue stick according to the present invention (formula 1) whatever the type of paper used.


Claims

1. Water based glue stick composition comprising adhesive and nanocrystalline cellulose.
 
2. Water based glue stick composition according to claim 1, wherein the nanocrystalline cellulose is obtained by sulfuric acid hydrolysis of cellulose, advantageously the nanocrystalline cellulose consists in cellulose hydrogen sulphate sodium salt nanoparticles.
 
3. Water based glue stick composition according to any of claim 1 or 2, wherein the nanocrystalline cellulose has a particle diameter in the range 2-8 nm, preferably in the range 2 - 5 nm measured by atomic force microscopy.
 
4. Water based glue stick composition according to any of claim 1 to 3, wherein the nanocrystalline cellulose has a particle length in the range of 40-160 nm, preferably in the range 44-108 nm, measured by atomic force microscopy.
 
5. Water based glue stick composition according to any one of claims 1 to 4, wherein the nanocrystalline cellulose content is in the range 0.1-3 weight % based on the total weight of the glue stick composition, advantageously in the range 0.2-2 weight % based on the total weight of the glue stick composition, more advantageously in the range 0.25-1.5 weight % based on the total weight of the glue stick composition.
 
6. Water based glue stick composition according to any one of claims 1 to 5, wherein the adhesive is selected in the group consisting of starch, starch derivatives, polyvinylpyrrolidone, aqueous polyacrylates, polyvinyl alcohols and mixture thereof, advantageously in the group consisting of starch, starch derivatives and mixture thereof.
 
7. Water based glue stick composition according to any one of claims 1 to 6, wherein the adhesive content is in the range 15-35 weight % based on the total weight of the glue stick composition, advantageously in the range 17-32 weight % based on the total weight of the glue stick composition, still more advantageously in the range 22-27 weight % based on the total weight of the glue stick composition.
 
8. Water based glue stick composition according to any one of claims 1 to 7, wherein it comprises a humectant, advantageously selected in the group consisting of glycerin, sorbitol, aloe Vera, honey, propylene glycol, butylene glycol and mixture thereof, more advantageously selected in the group consisting of glycerin, sorbitol and mixture thereof.
 
9. Water based glue stick composition according claim 8, wherein the humectant content is in the range 5-30 weight % based on the total weight of the glue stick composition, advantageously in the range 10-25 weight % based on the total weight of the glue stick composition, still more advantageously in the range 15-20 weight % based on the total weight of the glue stick composition.
 
10. Water based glue stick composition according to any one of claims 1 to 9, wherein it comprises a soap, advantageously selected in the group consisting of sodium salt of fatty acid, more advantageously it is sodium stearate.
 
11. Water based glue stick composition according to any one of claims 1 to 10, wherein the glue stick composition contains other additives, advantageously selected in the group consisting of antifoam agent, preservative, perfume, pH regulators, pH indicators, lubricants, wetting agents, plasticizers, fillers, superabsorbers, coloring agents such as dyes or pigments or mixture thereof and mixture thereof.
 
12. Glue stick containing the glue stick composition according to any one of Claims 1 to 11.
 
13. Use of a glue stick according to Claim 12 for planar joining of substrates, in particular for joining paper and/or cardboard, to one another, in particular printer paper, photo paper and cardboard paper.
 





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Cited references

REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description